Learning with AirSketcher

AirSketcher turns airflow simulation into an accessible virtual laboratory. Students can sketch a model, form a hypothesis, run a simulation, inspect the flow field, and defend a design decision with visual and numerical evidence.

The activities in this manual progress from introductory drag and wake studies to applied environmental flow, passive ventilation, aerodynamic coefficients, flow measurement, and Reynolds-number similarity. They are suitable for middle school and high school science, physics, environmental science, design and technology, and STEM project work.

Learning Goals

Students use AirSketcher to:

Curriculum Connections

Level Subject area Typical topics in this manual
Middle school General science Wind, pressure, force, basic airflow, fair testing
High school Physics Fluid mechanics, drag, lift, pressure, energy
High school Environmental science Urban wind, ventilation, PM2.5 dispersion, exposure metrics
STEM / engineering Design and technology Wind-resistant structures, passive design, digital twins
Advanced Aerodynamics and measurement Airfoils, orifice meters, dimensional similarity

Teaching Features

  1. Predict: State a hypothesis and identify the variables.
  2. Simulate: Keep controlled settings constant and wait for a stable solution.
  3. Measure: Use the same probes, locations, scales, and units in every case.
  4. Analyze: Calculate the requested metrics and compare patterns as well as numbers.
  5. Explain: Connect the evidence to fluid-dynamics concepts and acknowledge limitations.
  6. Improve: Propose and test a revised design.

Modeling note: AirSketcher is an educational simulation environment. Results depend on geometry, boundary conditions, mesh resolution, solver settings, and the assumptions of a 2D model. Use the labs to compare controlled scenarios and explain trends; do not treat classroom results as a substitute for certified engineering analysis.

Audience and Access

Activity Set: 10 Labs

The body of this manual contains the following 10 labs. Titles, grade ranges, and topics below match the detailed activities that follow.

Foundation: Forces, Drag, and Fair Testing

Lab 1: Obstacle Flow Analysis (Golf Ball)

Lab 2: Signage / Tent Design - Reducing Wind Load

Applied Flow: Built Environment, Energy, and Air Quality

Lab 3: Wind Flow Around a Group of Buildings

Lab 4: Wind Speed-Up on Hills Using an ABL Profile

Lab 5: How Clogged Filters Increase Fan Energy Consumption

Lab 6: Green Walls and PM2.5 Analysis in Schools

Lab 7: Wing Walls for Home Ventilation

Advanced: Aerodynamics, Measurement, and Similarity

Lab 8: Lift and Drag Analysis on a NACA 2412 Airfoil

Lab 9: Measuring Airflow with an Orifice Meter

Lab 10: Model Scaling and Reynolds Number Similarity

Lab 1: Obstacle Flow Analysis (Golf Ball)

1) Objectives

2) Theoretical Background

2.1 Boundary Layer and Flow Separation

Knowledge Nugget: Smooth Sphere vs. Golf Ball

Knowledge Nugget: Why does turbulence help reduce drag?

Knowledge Nugget: Front Push vs. Rear Suction

3) Hypothesis

Before running the simulation, write your predictions:

(After the lab, return here and check whether your predictions were correct.)

Teacher Answer - Section 3

4) Equipment / Software

Important Comparison Note

To make the smooth ball and golf ball results comparable, use the same domain size, ball diameter, and ball position for both simulations.

The smooth ball and golf ball should occupy the same size and location within the flow domain. The pressure box probe must also have the same size and be placed in the same relative position for both cases.

This ensures that any differences in wake size, pressure, and drag are caused by the ball surface texture, not by differences in geometry or probe placement.

5) Experimental Procedure

  1. Create the flow domain.
    Click the Image Processor icon.

  1. Open the smooth-ball or golf-ball image file. In Expert Options, choose Set Domain Height (Y) and then Calibrate Height by Drawing. Draw across the ball diameter, enter 0.1 m, place the ball in the domain, and click Export to Simulation.
Open the image of balls
Set the height of domain in the ‘Expert Options’
Calibrate the height of ball

  1. Repeat the same loading and placement process for the golf ball model.
    Make sure the golf ball has the same diameter and is placed in the same position in the domain as the smooth ball.

  2. Set the inlet air velocity to 50 m/s for both models. Do not compare pressures or forces from cases that use different inlet speeds.

inlet velocity.jpg
  1. Run the simulation for both models.
    Wait until the computation converges. The LED indicators for Vx, Vy, and Pressure should turn green or at least yellow.

  1. Observe the following for each model:

  1. Measure the pressure drop across each ball using the box probe tool.

  1. Read the pressure in front of and behind each ball from the front and rear faces of the box probe.

Probe Placement Check

Before recording your values, confirm that the pressure box probe has the same size and the same relative position for the smooth ball and the golf ball.

For example, the front and rear faces of the probe should be located at equivalent distances from the center of each ball. This makes the pressure readings fair to compare.

6) Results Table

Use the same measurement setup for both models.

Model Streamlines Wake Size P front P rear ΔP
Smooth Sphere Early separation Large
Golf Ball Delayed separation Small

ΔP = Pfront − Prear

Teacher Answer - Section 6

Expected qualitative trend at the same velocity

Model Typical separation Typical wake Expected pressure-drag trend
Smooth ball Earlier in the intended comparison Wider Higher
Dimpled ball Later in the intended comparison Narrower Lower

Exact pressures and wake dimensions depend on Reynolds number, geometry, roughness treatment, turbulence model, domain size, and probe placement. Use the simulated trend as the comparison criterion rather than an assumed numerical range.

Modeling check: A dimple benefit is expected only in a Reynolds-number range where the roughness changes boundary-layer transition. A 2D cross-section behaves like a cylinder per unit depth, not a true 3D sphere. Confirm that the chosen AirSketcher model represents the intended roughness effect before presenting the result as golf-ball aerodynamics.

7) Data Analysis

7.1 Wake Zone Comparison

Teacher Answer - 7.1

7.2 Pressure Difference Calculation

Using the values from your Results Table, fill in:

Answer the following:

Teacher Answer - 7.2

For example, if Pfront = +70 Pa and Prear = −100 Pa, then:

ΔP = 70 − (−100) = 170 Pa

In this illustrative case, the rear reading has the larger magnitude: 100/170 ≈ 59%, compared with 70/170 ≈ 41% for the front reading. This split is not universal; it changes with geometry, Reynolds number, and the exact locations and averaging used by the probes.

7.3 Linking ΔP to Drag

For a simple classroom estimate using representative face-averaged pressures, the pressure-drag magnitude is:

FD, p ≈ ΔP Af

where Af is frontal area. The exact pressure force is the surface integral Fp = −∫Sp n dS; use AirSketcher’s integrated Fx result when available.

For reference, the Reynolds number for a 0.1 m ball at 50 m/s is approximately:

$$ Re=\frac{VD}{\nu}=\frac{(50\ \text{m/s})(0.1\ \text{m})}{1.5\times10^{-5}\ \text{m}^2/\text{s}}\approx3.3\times10^5 $$

Teacher Answer - 7.3

Frontal area:

Af = π(0.05 m)2 ≈ 7.85 × 10−3 m2

Use the measured pressure differences rather than assumed values:

Model Measured pressure difference Estimated 3D pressure drag
Smooth sphere ΔPsmooth FD, p ≈ ΔPsmooth(7.85 × 10−3) N
Golf ball ΔPgolf FD, p ≈ ΔPgolf(7.85 × 10−3) N

The case with the larger measured ΔP has the larger pressure-drag estimate. AirSketcher’s integrated Fx is preferred because it uses the resolved surface-pressure distribution. If the simulation is strictly 2D, report force per unit depth in N/m rather than treating it as the force on a 3D sphere.

7.4 The Surprise: Roughness Reduces Drag

Most people expect a rougher surface to cause more drag, like friction on a road.

Teacher Answer - 7.4

On a smooth sphere, the boundary layer remains laminar and has little momentum near the surface. When the flow reaches the widest part of the ball and the pressure begins to rise, the laminar boundary layer cannot overcome this adverse pressure gradient and separates early. This early separation point creates a large wake behind the ball, where the pressure is very low due to suction. The large pressure difference between the high-pressure front and the low-pressure wake produces a large drag force.

On the golf ball, the dimples cause the boundary layer to transition to turbulence early. A turbulent boundary layer has more momentum near the surface and can resist the adverse pressure gradient for longer, so the separation point moves farther around toward the rear of the ball. The smaller wake means the rear pressure, or suction, is less severe. This reduces the pressure difference and therefore reduces the drag force.

In this case, roughness helps not by reducing friction, but by energizing the boundary layer so that it stays attached longer.

8) Discussion Questions

Q1 - Wake Zone and Drag

Which model has a smaller wake zone, and why? Trace the full chain:

Surface texture → boundary layer behavior → separation point → wake size → rear pressure → drag force

Use your contour images as evidence.

Teacher Answer - Q1

The golf ball has a smaller wake zone.

Full chain:

Dimpled rough surface → boundary layer becomes turbulent earlier → turbulent boundary layer has higher near-wall momentum → separation point moves farther toward the rear of the ball → wake becomes narrower and shorter → rear pressure becomes less negative → pressure difference becomes smaller → drag force decreases.

Evidence from the contour: On the velocity contour, the smooth sphere shows a wide, elongated dark blue, near-zero velocity region extending 2-3 diameters behind the ball. The golf ball shows a much smaller dark region, with the flow recovering to normal speed much sooner downstream.

Q2 - Why Turbulence Helps

It seems strange that making a surface rougher and causing more turbulence actually reduces drag. Write a clear explanation in 4-5 sentences that you could use to explain this to a friend who has not done this lab. Write it as a connected argument, not just bullet points.

Teacher Answer - Q2

When air flows around a smooth ball, it forms an orderly, layered flow called a laminar boundary layer close to the surface. This laminar layer is fragile. When it reaches the back half of the ball, where the air pressure starts to rise again, it cannot stay attached and peels away from the surface early. This leaves a large turbulent wake behind the ball, which acts like a low-pressure bubble that pulls the ball backward.

The dimples on a golf ball deliberately break up this smooth flow and create a thin turbulent boundary layer instead. Although this sounds like it would cause more resistance, the turbulent layer is actually better at staying attached to the surface. Because it separates later, it leaves a smaller wake. A smaller wake means less rear suction, a smaller pressure difference, and therefore less drag.

This is why a deliberately roughened ball flies farther than a perfectly smooth one.

Q3 - The Rear Suction Effect

Your ΔP calculation may show that the rear gauge-pressure magnitude is larger than the front value. Use your own measurements to determine whether that occurs, then explain the separated wake and incomplete pressure recovery.

Hint: Think about separation, momentum loss, recirculation, and incomplete pressure recovery in the wake.

Teacher Answer - Q3

At the front of the ball, flow decelerates toward the stagnation point and static pressure rises. The speed reaches zero only at the ideal stagnation point, not across the entire front surface.

Behind the ball, the flow has separated and the wake is filled with slow-moving, recirculating fluid. The fast-moving freestream flow rushing past the sides of the ball creates a shear layer at the edge of the wake. This shear layer draws momentum out of the wake region and keeps the fluid inside the wake nearly stagnant.

Separation prevents complete pressure recovery on the rear surface. The resulting pressure deficit contributes to pressure drag; its share of total drag must be determined from the simulated pressure distribution or integrated forces.

Q4 - Real-World Applications

The dimple principle is used beyond golf balls. For each application below, explain how the same idea - using surface features to delay separation and shrink the wake - applies.

Application How the dimple principle applies
Racing car body panels
Shark-skin swimsuit fabric
Texture on wind turbine blades
Automotive side mirrors

Teacher Answer - Q4

Application How the dimple principle applies
Racing car body panels Small surface features or carefully designed curves trip the boundary layer into turbulence, delaying separation over the rear bodywork and reducing the size of the low-pressure wake behind the car. This lowers pressure drag, which is the dominant drag source at racing speeds.
Shark-skin swimsuit fabric The ribbed microstructure, inspired by shark scales, creates small-scale turbulence in the boundary layer close to the skin, reducing separation and drag in water.
Texture on wind turbine blades Turbine blades operate at varying angles of attack. Surface texture near the leading edge helps maintain attached flow across a wider range of conditions, improving the lift-to-drag ratio and energy output.
Automotive side mirrors Modern side mirrors use carefully shaped housings and sometimes small surface vanes to guide airflow smoothly around the mirror and prevent a large separated wake, which would otherwise create noise, vibration, and aerodynamic drag at highway speeds.

9) Extension Ideas

10) Grade Level / Indicators

Grade: 8-10
Indicators: Sci 3.2 Gr.8/1 - Explain forces acting on objects; Sci 3.2 Gr.10/1 - Analyze drag forces in fluids.
Subjects: Science / Basic Physics

Lab 2: Signage / Tent Design - Reducing Wind Load

1) Objectives

Wind-load failure example

2) Simulation Setup (Important!)

Knowledge Nugget: Solid vs. Perforated Signs

  • Solid sign: Wind hits the full area → High front pressure → High Drag.
  • Perforated sign: Air passes through partially → Reduces front-to-back pressure difference.
  • Reduced pressure difference → Fx decreases.
  • This uses the same principle as “reducing wind-facing area” to lower applied forces.

Knowledge Nugget: Upright vs. Angled Signs

  • 90° Upright sign: Takes full wind load → High pressure drag.
  • 30° Angled sign: Redirects some force → Reduced Drag.
  • The tilt allows wind to flow more smoothly over the surface.
  • Angling acts as a form of aerodynamic shaping.

Knowledge Nugget: Front Push vs. Rear Suction

  • Most people assume drag is caused by wind pushing the front face of the sign.
  • Front pressure and rear pressure recovery both affect the net drag; inspect the pressure map before deciding which contribution is larger.
  • A larger wake = deeper vacuum behind = stronger pull from behind = higher Fx.
  • Anything that shrinks the wake - perforations or tilting - directly reduces this rear suction.

3) Equipment / Software

4) Experimental Procedure

  1. Create the flow domain.
  2. Place the first sign model in position.
  3. Set Inlet Velocity (e.g., 20 m/s).
Setting the inlet wind speed
  1. Run the Simulation.
  2. Open Pressure Contour:
    • Check Box probe
  3. Read values from the Pressure (box) probe window:
    • Fx
Read the total force Fx, pressure at the front and the back of the signage
  1. Record values and save the box probe window screenshot.
  2. Change the sign model → Repeat the steps (using the same velocity).

5) Results Table

Sign Type Fx (N/m) Analysis
Solid Sign
Perforated Sign
30° Angled Sign

Teacher Answer - Section 5 (expected ranking at V = 20 m/s) - Solid Sign: Fx - highest value, full frontal area with large rear suction wake. - Perforated Sign: Fx - reduced because air bleeds through, partially filling the wake and reducing rear suction. - 30° Angled Sign: Fx - lowest because the tilted surface deflects flow rather than blocking it, dramatically shrinking the wake. - Exact values depend on sign dimensions and porosity settings. What matters is the consistent ranking: Solid > Perforated > Angled.

6) Data Analysis

6.1 Pressure Map Interpretation

Look at your pressure contour screenshots for the Solid Sign and answer:

Hint: A dark blue region behind the sign means strongly negative (suction) pressure. Drag comes from the difference between front and rear pressure - not just the push from the front.

Teacher Answer - 6.1 - The front face shows higher (positive) pressure - yellow/orange on the contour - because incoming wind decelerates as it hits the sign, converting kinetic energy to pressure (stagnation effect). - The rear face shows lower (negative) pressure - dark blue on the contour - because the flow separates at the sign edges, leaving a large low-velocity wake with a deep suction zone. - Both faces contribute to the pressure force. The larger contribution must be determined from area-averaged pressure or the integrated force result; it should not be assumed from color alone. - The contour image shows wind does not just push - the dark region behind the sign is “pulling” it in the wind direction, like a vacuum.

6.2 Comparing the Three Designs

Calculate the percentage reduction in Fx compared to the Solid Sign:

$$ \mathrm{Reduction}\,[\%]= \frac{F_{x,\mathrm{solid}}-F_{x,\mathrm{design}}}{F_{x,\mathrm{solid}}}\times100 $$

Sign Type Fx (N/m) Reduction (%)
Solid Sign - (baseline)
Perforated Sign
30° Angled Sign

Teacher Answer - 6.2 - In the intended model, tilting is expected to reduce Fx more than the selected perforation pattern. Report the measured reductions; do not use a generic percentage as an acceptance range. - Evidence from contour: the angled sign shows a much smaller dark blue wake region - the flow is deflected over and under the tilted surface rather than fully separating. The perforated sign’s wake is smaller than the solid sign but still present, because only some air bleeds through. - Key point for students: the dark suction zone shrinks the most behind the angled sign - directly explaining why its Fx is lowest.

6.3 The Rear Suction Effect

Teacher Answer - 6.3 - If the front-to-rear pressure difference were eliminated in an idealized comparison, the pressure-drag component would approach zero, although skin-friction drag could remain. - Explanation of the pull: The solid sign creates a separated, turbulent wake with incomplete pressure recovery. Lower rear-face pressure contributes a downstream force alongside the front-face pressure. Bernoulli’s equation should not be applied directly across this dissipative wake. - Perforations help because they allow a small amount of air to pass through the sign and flow into the wake. This partially re-pressurises the wake - raising the rear pressure from strongly negative toward zero - which reduces the front-to-rear pressure difference and therefore reduces Fx. The sign is the same size, but the wake is smaller and less severe.

6.4 Real-World Connection

Choose one example: a highway truck, a boat sail, or a roadside billboard. Then:

  1. Sketch a simple side-view diagram with wind acting on it.
  2. Mark where you expect high pressure (front) and low pressure / suction (rear).
  3. Suggest one design modification inspired by your lab results.
  4. Write 2-3 sentences using the words: pressure difference, wake, and drag force.

Teacher Answer - 6.4 (Highway Truck example) - Sketch: Truck viewed from the side. High pressure (+) marked on the flat front cab face. Low pressure (−) marked behind the trailer (large separated wake). - Design modification: Add a boat-tail fairing to the rear of the trailer (tapered panels that partially close the back), similar to how the angled sign deflects flow. This reduces the size of the wake and raises the rear pressure, directly reducing the pressure difference between front and back. - Sentences: “A highway truck has a large flat rear face that creates an extensive separated wake behind it. The pressure difference between the front and the incomplete pressure recovery at the rear contributes strongly to the truck’s drag force. Adding tapered rear panels can reduce the wake size, raise rear pressure, and reduce drag.” - Other acceptable answers: Billboard (add perforated panels or tilt at angle), Boat sail (adjust sail angle to reduce separation on the leeward side).

7) Discussion Questions

Q1 - Best Design for High-Wind Areas

The 30° Angled Sign reduces drag the most - but is it always the best real-world choice? Fill in the table, then write a recommendation:

Factor Solid Sign Perforated Sign 30° Angled Sign
Wind drag (low = good)
Visibility to public
Ease of installation
Cost / complexity
Stability in rain

Recommendation: Which design would you choose for an outdoor event beside a river where wind regularly reaches 15 m/s? Write 3-4 sentences justifying your answer using at least two factors - not just drag force.

Teacher Answer - Q1

Factor Solid Sign Perforated Sign 30° Angled Sign
Wind drag (low = good) Poor Good Best
Visibility to public Best Good Reduced (angled away)
Ease of installation Best Good More complex (angled frame needed)
Cost / complexity Lowest Medium Highest
Stability in rain Good Good (drains through holes) Good (water runs off)

Sample Recommendation: For a riverside event at 15 m/s, the perforated sign may offer the best balance. While the angled sign has lower drag in the intended comparison, its tilted orientation can reduce visibility for a public-facing banner. The perforated sign lowers the measured Fx, drains rainwater well, and can be installed on a standard upright frame. If structural load is the primary concern and visibility is secondary, the angled sign may be preferable. A real installation still requires a qualified wind-load design. - Accept any well-reasoned answer that references at least two factors with aerodynamic justification.

Q2 - Wind Speed and Force: The Squared Relationship

(a) Predict first (before calculating):

If wind speed doubles from 5 m/s to 10 m/s, what happens to Fx?

Write your prediction and reasoning here: ______________________

Teacher Answer - Q2a Correct answer: It quadruples (×4). Most students will predict ×2 (doubling) because doubling the speed feels like it should double the force. This is a valuable misconception to address - the squared relationship is not intuitive and has real safety consequences.

(b) Calculate using the drag force formula:

$$ F_x=\frac{1}{2}\rho V^2 C_D A_{\mathrm{ref}} $$

If V doubles (V new = 2V), substitute into the formula and show mathematically by how many times Fx increases. Show your working.

Teacher Answer - Q2b

$$ F_{x,\mathrm{new}}=\frac{1}{2}\rho(2V)^2C_DA_{\mathrm{ref}} $$

$$ =\frac{1}{2}\rho(4V^2)C_DA_{\mathrm{ref}} $$

$$ =4\left(\frac{1}{2}\rho V^2C_DA_{\mathrm{ref}}\right) $$

 = 4Fx, original

Therefore Fx increases by 4 times when wind speed doubles. The key step is that (2V)² = 4V² - squaring the 2 gives the factor of 4.

(c) Check your prediction:

Teacher Answer - Q2c

$$ V_{\max}=5\sqrt{\frac{2000}{500}}=10\ \text{m/s} $$

At 10 m/s, Fx = 4(500) = 2, 000 N/m, exactly the rated limit under the constant-CD assumption. A higher speed exceeds it.

(d) Think further:

Wind speed during a storm can jump from 5 m/s to 20 m/s suddenly. By how many times does the force increase? Does this help explain why signs collapse suddenly during storms rather than gradually?

Teacher Answer - Q2d - V increases from 5 to 20 m/s - a factor of 4 in speed. - Force factor = (20/5)² = 4² = 16 times the original force. - A sign rated for 500 N/m at 5 m/s would experience 8000 N/m at 20 m/s - 16 times its safe load. - Yes, this directly explains sudden collapses. Because force scales with V², a gradual increase in wind speed produces a rapidly accelerating increase in load. The structure may appear fine up to a certain speed, then fail almost instantly as the load jumps far beyond the design limit. This is why storm collapses appear sudden even when wind has been building gradually.

Q3 - Learning from Real Failures

Large outdoor banners sometimes collapse during sudden wind gusts at riverside festivals. Based on your results, propose two specific design rules for installing a large banner in an open outdoor area. For each rule, give the aerodynamic reason using terms from this lab (Fx, pressure, drag, wake).

Rule 1: ______________________

Rule 2: ______________________

Teacher Answer - Q3 Many valid answers are acceptable. Strong answers will reference specific lab findings.

Sample Rule 1: Use a perforated or mesh banner fabric instead of solid material. Aerodynamic reason: A solid banner creates a large separated wake with incomplete rear pressure recovery. Perforations allow air to bleed through and can reduce the front-to-rear pressure difference, lowering Fx without changing the banner’s overall outline.

Sample Rule 2: Install the banner at an angle of 20-30° from vertical rather than fully upright, or provide a mechanism to tilt it automatically in high wind. Aerodynamic reason: A fully upright (90°) sign takes the maximum frontal wind load - all incoming momentum is blocked. Tilting the sign reduces the effective frontal area and allows flow to deflect over the surface rather than fully separating, shrinking the wake and reducing drag. Our simulation showed the 30° angled sign produced the lowest Fx of all three designs.

Other acceptable rules: Over-design the structural anchoring for V² scaling (not linear); use a guy-wire system rated for storm speeds; install a breakaway hinge that allows the sign to fold flat in extreme wind.

8) Extension Ideas

9) Grade Level / Indicators

Grade: 7 - 8

Indicators:

Subjects:

Lab 3: Wind Flow Around a Group of Buildings (2D Top-View Simulation)

1) Objectives

By the end of this lab, students will be able to:

2) Basic Concepts

The local velocity ratio may be used to compare locations:

$$ R_v = \frac{U_{\text{local}}}{U_{\text{reference}}} $$

where Ulocal is the wind speed at a measurement point and Ureference is the undisturbed incoming wind speed.

R value

Knowledge Nugget: Building Orientation Matters

  • Keep the prevailing-wind direction fixed when comparing orientations.
  • Rotate the entire building group, not individual buildings, for the main comparison.
  • Keep building shapes, spacing, wind speed, and simulation settings unchanged.
  • Observe pedestrian spaces, courtyards, entrances, and paths between buildings.
  • A better orientation should avoid both large stagnant zones and uncomfortable high-speed corridors.
  • Increasing the incoming wind speed is not the purpose of this experiment; the aim is to study how orientation redirects the same wind.

3) Equipment / Software

4) Experimental Variables

Variable Type Variable
Independent variable Orientation angle of the entire building group relative to the prevailing wind
Dependent variables Local wind speed, velocity ratio, pressure pattern, wake size, shelter-zone area, and pollutant/particle movement
Controlled variables Building geometry, building spacing, incoming wind speed, wind direction, domain size, measurement points, display scale, and all solver settings

Choose a small rotation angle such as 10°-30°, or use the angle assigned by the teacher. Record the exact value; do not write only “a few degrees.”

5) Experimental Procedure

Part A: Prepare the Common Model

  1. Draw or import the plan of the complete building group.
  2. Set the reference incoming wind speed, Ureference, as instructed by the teacher.
  3. Select at least five fixed measurement locations. Recommended locations are:
    • Upwind open area
    • Entrance to the building group
    • Gap or street between buildings
    • Central courtyard or shared open space
    • Leeward side behind a large building
    • Downwind edge of the site
  4. Label the points P1, P2, P3, and so on. Use the same points in both simulation rounds.
  5. Save a screenshot of the model showing the buildings, prevailing-wind arrow, scale, and measurement points.

Round 1: Baseline Orientation - Scenario A

  1. Set the building group to the original orientation and record its angle as θA.
  2. Run the simulation until the displayed result is stable.
  3. Open and save the following results using the same color scale for both rounds:
    • Velocity map with streamlines
    • Pressure map
    • Pollution / Shelter Zones or particle-flow display, if available
  4. At every measurement point, record:
    • Local wind speed, Ulocal
    • Velocity ratio, Rv
    • Relative pressure or pressure category, if available
    • Flow observation, such as acceleration, shelter, wake, or recirculation
  5. Mark the major high-speed corridors and low-speed shelter zones on the screenshot.
  6. Note where particles or pollutants appear to remain trapped or disperse slowly.

Round 2: Rotated Orientation - Scenario B

  1. Duplicate Scenario A.

  2. Rotate the entire building group by the selected small angle Δθ. Do not change the prevailing-wind direction.

    θB = θA + Δθ

  3. Confirm that all building shapes, spacing, wind settings, domain settings, and measurement points remain equivalent to Scenario A.

  4. Run the simulation until the displayed result is stable.

  5. Save the same result maps with the same legends, color ranges, view scale, and camera position used in Scenario A.

  6. Record the local wind speed, velocity ratio, pressure, and flow observation at every measurement point.

  7. Compare the two scenarios side by side. Highlight areas where the small rotation:

    • Opened or blocked a wind path
    • Shifted a building wake
    • Enlarged or reduced a shelter zone
    • Increased wind speed through a gap
    • Improved or weakened pollutant dispersion
Example of group building rotation

6) Results Tables

Table 1: Simulation Settings

Setting Scenario A: Baseline Scenario B: Rotated
Building-group orientation, θ (°)
Rotation difference, Δθ (°) 0
Prevailing-wind direction (° or compass direction) Same as A
Reference wind speed, Ureference (m/s) Same as A
Other solver settings Same as A

Table 2: Point Measurements

Point / Area UA (m/s) Rv, A UB (m/s) Rv, B Change in Speed (%) Main Observation
P1: Upwind open area
P2: Site entrance
P3: Gap between buildings
P4: Central courtyard
P5: Behind a large building
P6: Downwind edge

Calculate the percentage change in local wind speed using:

$$ \%\Delta U = \frac{U_B-U_A}{U_A}\times100 $$

If UA = 0, report the absolute difference UB − UA instead of calculating a percentage.

Table 3: Overall Site Comparison

Indicator Scenario A: Baseline Scenario B: Rotated Better Scenario Evidence
Size of low-speed shelter zones
Strength/extent of high-speed corridors
Wake and recirculation behind buildings
Ventilation of courtyards/open spaces
Pollutant or particle dispersion
Overall wind comfort and ventilation

7) Data Analysis

Students should:

  1. Calculate Rv for every measurement point in both scenarios.
  2. Calculate the percentage change in wind speed where possible.
  3. Compare the location and size of wakes, recirculation regions, shelter zones, and accelerated-flow regions.
  4. Relate pressure differences to the direction of air movement around and between the buildings.
  5. Explain why some locations show a large change even though the building group was rotated by only a few degrees.
  6. Decide which orientation provides the better overall result. Support the decision with numerical measurements and map evidence.
  7. State any trade-off. For example, an orientation may improve courtyard ventilation but create an uncomfortable high-speed path near an entrance.

8) Discussion Questions

  1. Which parts of the site were most sheltered in Scenario A? Did those areas move in Scenario B?
  2. Which gaps between buildings accelerated the wind, and why?
  3. How did the rotation change the windward and leeward sides of the buildings?
  4. Why can a small change in orientation produce a large change in a wake or wind corridor?
  5. Which scenario would provide better wind-driven natural ventilation for the building group? Give evidence.
  6. Which scenario would provide better pedestrian wind comfort? Is it the same scenario as the one with the strongest ventilation?
  7. Where might pollutants, heat, or moisture accumulate in each scenario?
  8. What are the limitations of using a 2D top-view model for real buildings with different heights?

Teacher Answer - Discussion Questions

  1. The most sheltered locations are normally on the leeward sides of buildings and inside recirculating courtyards. When the group rotates, the windward and leeward faces change, so the sheltered regions should move as well. Students should identify the movement from matched velocity maps.
  2. Wind accelerates through gaps that constrict or channel the approaching flow. The strongest corridor is usually the gap aligned most directly with the incoming wind, especially where the local pressure difference drives flow through a narrow passage.
  3. Rotation changes which faces receive positive windward pressure and which faces sit in lower-pressure wakes. Compare the pressure contours at the same legend range to show the change.
  4. Separation points and jet paths are sensitive to geometry. A small rotation can redirect a gap jet, attach it to a different wall, or move a wake across a measurement point, producing a large local change.
  5. The better ventilation case is the one with stronger, more continuous airflow through occupied spaces without isolated dead zones. A complete answer cites at least two matched Rv measurements and the corresponding contour evidence.
  6. Better pedestrian comfort normally means avoiding both stagnant regions and excessive high-speed jets. It may not be the same case as maximum ventilation; students should state the trade-off and use the same comfort criterion for both scenarios.
  7. Pollutants, heat, and moisture tend to accumulate in low-speed recirculation zones, enclosed courtyards, and deep wakes where removal is slow.
  8. A 2D top view omits roof-level flow, downwash, vertical mixing, buoyancy, different building heights, and three-dimensional turbulence. It is suitable for controlled horizontal comparisons, not final pedestrian-wind or ventilation certification.

9) Conclusion

Write a short conclusion of 150-200 words that:

10) Extension Ideas

11) Submission Checklist

Submit:

12) Grade Level / Indicators

Grade: 11-12 / introductory undergraduate

Indicators:

Subjects:

Lab 4: Wind Speed-Up on Hills Using an ABL Profile

(Wind Speed-Up on Hill with Atmospheric Boundary Layer - 2D Side View)

1) Objectives

2) Theoretical Concepts

Atmospheric Boundary Layer (ABL)

The ABL is the layer of the atmosphere closest to the Earth’s surface (roughly the first 0-1000 m).

Key characteristics: - Wind speed increases with altitude. - Caused by surface friction (surface roughness). - Slow wind near the ground, faster wind higher up.

This can generally be approximated using the Power Law Profile:

Power_Law_Wind_Profile.png

$$ u(z) = u_{ref} \left( \frac{z}{z_{ref}} \right)^{\alpha} $$

where:

In this experiment: - uref = 10 m/s
- zref = 10 m
- α = 0.16

What is Topographic Speed-Up?

When ABL flow passes over a hill: - Airflow is compressed at the top. - Streamlines become denser. - Wind speed increases at the crest. - Flow separation may occur behind the hill.

This phenomenon is called Wind Speed-Up.

Knowledge Nugget: Why is the wind stronger at the peak?

  • The terrain displaces and bends the approaching streamlines.
  • The pressure field around the hill accelerates the flow over the crest.
  • Streamline compression can accompany this acceleration, but there is no literal roof forming a closed nozzle above the hill.
  • The higher and steeper the hill → The more pronounced the Speed-up.

Knowledge Nugget: Behind the Hill (Lee Side Effect)

  • Recirculation zones (eddies) may form.
  • Wind speed decreases.
  • High turbulence can occur in some cases.
  • This is a high-risk zone for buildings or structures.

3) Simulation Setup

Expert Options

4) Equipment / Software

5) Experimental Procedure

  1. Draw flat ground + a hill (e.g., 5 m high).
  2. Enable ABL and set α = 0.16.
  3. Set uref = 10 m/s.
  4. Run the Simulation.
  5. Measure velocity at:
    • Upwind (at the same elevation as the crest)
    • Crest
    • Lee Side
  6. Open Streamline View to observe streamline density.
  7. Change hill height (10, 15, 20 m).
  8. Repeat and record data.

6) Calculations

Speed-Up Factor

$$ S=\frac{U_{\mathrm{crest}}(z_c)}{U_{\mathrm{upwind}}(z_c)} $$

Both velocities must be measured at the same elevation zc as the crest.

If: - Value > 1 → Flow acceleration occurred - Value = 1 → No effect - Value < 1 → Velocity decreased

Hill speed-up result

7) Results Table

Hill Height (m) U Upwind (m/s) U Crest (m/s) U Lee Side (m/s) Speed-up Factor Analysis
5
10
15
20

8) Data Analysis

Students should:

  1. Compare the Speed-up Factor across different heights.
  2. Analyze how hill height correlates with wind acceleration.
  3. Observe the formation of recirculation behind the hill.
  4. Connect findings to the ABL equation.

9) Discussion Questions

  1. Which hill height produced the greatest Speed-up?
  2. What happens to the flow behind the hill?
  3. If α is changed to 0.3 (rougher surface), how will the results change?
  4. Why are mountain peaks ideal for installing wind turbines?
  5. What type of structures should be avoided behind a hill?

Teacher Answer - Discussion Questions

  1. The greatest speed-up is the case with the largest measured S = Ucrest/Uupwind at the same sampling height. A taller or steeper hill may increase acceleration, but excessive steepness can also cause separation, so the measured result controls the answer.
  2. The flow expands and decelerates on the lee side. If the adverse pressure gradient is strong enough, it separates and forms a low-speed recirculation zone with elevated turbulence.
  3. With the same uref and zref, increasing α creates stronger vertical shear and generally reduces inlet speed below zref. The crest and upwind speeds must be remeasured at the same height; the speed-up ratio cannot be inferred from α alone.
  4. Exposed ridges can have higher mean wind speed and therefore greater available wind power. Turbine siting must also consider turbulence, extreme gusts, access, structural loads, and environmental constraints.
  5. Avoid placing wind-sensitive or naturally ventilated structures in the strongest lee-side separation zone without further analysis. The simulation is a screening study; structural and planning decisions require site-specific professional assessment.

10) Extension Ideas

11) Grade Level / Indicators

Grade: 9, 11-12 / introductory undergraduate

Indicators:

Subjects:

Lab 5: How Clogged Filters Increase Fan Energy Consumption

(Digital Twin Filter Testing + Energy Analysis)

1) Objectives

2) Physics Concepts

What is a Digital Twin?

A Digital Twin is a virtual computer model of a physical system.
It allows us to experiment, compare, and predict outcomes without physical hardware.

Filters and Pressure Drop (ΔP)

When air flows through a filter, it encounters flow resistance.

More clogging → Lower porosity → Higher pressure drop (ΔP).

Key principle:

Pair = ΔP Q

$$ P_{\mathrm{elec}}=\frac{\Delta P\,Q}{\eta_{\mathrm{total}}} $$

where ΔP is in pascals, Q is volumetric flow in m3/s, and ηtotal is the combined fan, motor, and drive efficiency. If airflow is recorded in CFM, convert it before using SI units:

QSI = QCFM × 4.7195 × 10−4

Annual energy is E = Pelect/1000 in kWh when Pelec is in watts and t is in hours.

Knowledge Nugget: What is an Energy Penalty?

  • It is unnecessary excess energy consumption.
  • Caused by clogged filters forcing the fan to work harder.
  • Often goes unnoticed because the airflow (Q) seems “normal”.
  • Over a year, this can inflate electricity bills significantly.

Knowledge Nugget: Porous Media in Simulation

  • Used to represent filters in the software.
  • High porosity (80%) → Air passes easily.
  • Low porosity (30-50%) → Air struggles to pass.
  • Reducing porosity simulates a “clogged filter”.

3) Simulation Setup

4) Equipment / Software

5) Experimental Procedure

Round 1: Clean Filter

  1. Draw the system layout: Inlet → Filter → Fan → Outlet.

The positions of the air filter and the blower
  1. Set the filter porosity to 80%.
  2. Set the blower to 10 m/s at 0° (toward the right).
  3. Run the simulation.
  4. Click Analysis and Report.
  5. Save the PDF.
  6. Record:
    • CFM
    • Fan Energy (kWh/yr)
    • Cost/yr

Round 2: Dirty Filter

  1. Change the filter porosity to 50%.
  2. Run the Simulation again.
  3. Generate the PDF.
  4. Record from the Upstream table:
    • Δ Fan Energy
    • Δ Cost
Setting the clean filter (no filter = 100% porosity) and dirty filter

6) Reading the PDF Report

Select area and point of interest in front of the blower
Report setup: select upstream, add a comparison case, enter blower power, and enter the electricity tariff

Review the Comparison Summary Before Opening the Report

After the comparison case is added, AirSketcher first displays the Comparison Summary - Review Before Report window. This is a pre-report quality check: it appears before the full report is opened or the final PDF is generated.

Energy calculation report

Because this model uses a draw-through arrangement, select Exhaust / upstream. In the upper summary table, confirm that the Dirty case is listed as the AFTER case and review:

The lower Fan Energy, Cost, and Carbon Estimate table previews the annual BEFORE and AFTER values and their changes. Use it to confirm that the inputs, operating hours, electricity tariff, and case direction are correct before spending time opening the full report or generating its figures and PDF. Positive energy and cost changes indicate the annual Energy Penalty of the dirty filter.

7) Results Table

Important Note About the VFD

This activity assumes the blower uses a Variable Frequency Drive (VFD) with controls that maintain the required airflow. Therefore, the Clean and Dirty filter tests may show nearly the same CFM.

Under that control assumption, this is normal: the dirty filter creates more resistance, so the blower must generate a larger pressure rise and use more energy. Without airflow control, the operating point moves along the fan and system curves, and airflow will usually decrease instead.

Students do not need to calculate a drop in CFM if the blower maintains the same airflow.

Use line probe tool to check the CFD and pressure drop

Drawing line probe just behind the air filter
Condition CFM Filter Pressure Drop, ΔP (Pa) Energy (kWh/yr) Cost ($/yr)
Clean Filter
Dirty Filter
Difference: Dirty − Clean

The difference in annual energy use is the Energy Penalty:

Energy Penalty = Edirty − Eclean

The difference in annual cost is the Cost Penalty:

Cost Penalty = Cdirty − Cclean

8) Data Analysis

Step 1: Compare the Airflow

Compare the CFM for the Clean and Dirty filters.

Do not calculate a percentage drop in CFM when the airflow is being maintained by the VFD.

Step 2: Compare the Pressure Drop

Calculate how much the filter pressure drop increased:

ΔPincrease = ΔPdirty − ΔPclean

A dirty filter should have a greater pressure drop because it creates more resistance to airflow.

Step 3: Calculate the Energy Penalty

Energy Penalty = Edirty − Eclean

Step 4: Calculate the Cost Penalty

Cost Penalty = Cdirty − Cclean

Step 5: Explain the Results

Complete the following statement:

The CFM remained approximately the same because the VFD increased the blower output. However, the dirty filter caused a higher pressure drop, so the blower used more energy and cost more to operate.

9) Discussion Questions

  1. Were the Clean and Dirty filter CFM values approximately the same?

  2. Why can the CFM remain the same even when the filter becomes clogged?

  3. How much did the pressure drop increase when the filter became dirty?

  4. How much additional energy did the dirty filter use per year?

  5. How much additional money did the dirty filter cost per year?

  6. If a factory uses 20 identical blowers, calculate the total additional annual cost:

Total Additional Cost = 20 × Cost Penalty for One Blower

  1. Why might a clogged filter be difficult to notice in a VFD-controlled system?

  2. What information should be checked to decide when a filter needs replacement?

  3. How can a Digital Twin help a factory reduce energy and maintenance costs?

Teacher Answer - Discussion Questions

  1. In the VFD-controlled comparison, the clean and dirty cases should have approximately equal CFM if the controller successfully maintains the target flow.
  2. The VFD raises blower speed or command to overcome the additional filter resistance. Maintaining flow therefore requires more pressure rise and usually more electrical input.
  3. Calculate ΔPdirty − ΔPclean using the same upstream and downstream measurement locations.
  4. Calculate Edirty − Eclean from the report using the same operating hours and efficiency assumptions.
  5. Calculate Cdirty − Cclean using the same electricity tariff and currency.
  6. Multiply the cost penalty for one blower by 20 only if all blowers have the same duty cycle and operating conditions.
  7. A clogged filter may be difficult to notice because the VFD masks the airflow loss by increasing blower output. The warning signs are higher pressure drop, command, power, noise, or energy use.
  8. Check differential pressure, airflow, blower command or speed, power, operating hours, filter loading, indoor-air-quality requirements, and the manufacturer’s replacement limit.
  9. A Digital Twin can compare clean and loaded states, estimate energy and cost penalties, test maintenance thresholds, and prioritize replacement before airflow or air quality becomes unacceptable.

10) Extension Ideas

11) Grade Level / Indicators

Grade: 11-12 / introductory undergraduate

Indicators:

Subjects:

Lab 6: Green Walls and PM2.5 Analysis in Schools

(Flow Field → Particle Tracking / PM2.5 Pollution Analyzer)

1) Objectives

2) Key Terminology

3) Core Concepts

Knowledge Nugget: Why do Flow before Particle?

  • Particle Tracking doesn’t “guess” wind direction.
  • Particles only follow the pre-calculated Flow Field.
  • If the flow isn’t stable (streamlines are wobbling), PM2.5 results will be inaccurate.
  • Think of it as: “You must know the wind’s path before you can know the dust’s path.”

Knowledge Nugget: How do Green Walls help?

  • Trees act as drag → Wind speed drops.
  • Flow is forced up and over → Dust trajectory alters.
  • The wake zone behind the trees reduces direct wind-driven dust impacts.
  • Caution: If the wake zone is fully enclosed, local dust accumulation can occur.

4) Equipment / Software

5) Experimental Procedure

Part 1: Flow Simulation (Do this first)

  1. Draw the 2D layout:
    • Left = Road (Dust Source)
    • Right = School Zone
  2. Draw the Green Wall using a Porous Zone between the road and school.
Defining green wall (tree)
  1. Set Inlet parameters:
    • Inlet Velocity = 2-3 m/s
    • Direction: Left → Right
  2. Click Simulate (Run) until the Streamline/Velocity Maps stabilize.

Checkpoint: If the wind is still fluctuating, do not proceed to PM2.5 yet.

Part 2: PM2.5 Pollution Analyzer

Opening the pollution analyzer
  1. Click Show Result → enter Particle Tracking → select ** PM2.5 Pollution Analyzer**.
  2. Create dust source:
    • Tools → Traffic (Light)
    • Add Add Source and drag to cover the “Road” area.
  3. Set the Zone of Interest (ZOI):
    • Redraw Redraw Zone over the “Playground” or “Building Front”.
  4. Click START START to run the PM2.5 calculation.
  5. Use the ** PM2.5 Line Probe**:
    • Draw a line from “Road → through trees → into school”.
    • Observe how the concentration curve drops.

6) Reading the Results Correctly

Check the WHO 2021 Status box (or PM2.5 Audit Ledger): - Mean (µg/m³): Overall average in the ZOI. - P95 (µg/m³): Dust level in the worst-performing sectors of the ZOI. - WHO 2021 Status: AirSketcher’s color-coded comparison (e.g., GOOD / EXCEEDS WHO).

Health interpretation: The 2021 WHO PM2.5 guideline levels are 5 μg/m3 for the annual mean and 15 μg/m3 for the 24-hour mean. A short classroom simulation and its spatial P95 value are not, by themselves, a regulatory or clinical exposure assessment. Report the averaging period and treat the software status as an educational screening indicator.

Reading the Line Probe: - Note the shape of the graph (e.g., Sharp drop / Gradual decay / Flat / Spike).

Knowledge Nugget: Why look at P95 instead of just Mean?

  • Mean can be diluted by large areas of clean air.
  • P95 tells you what the “worst-off students” are breathing.
  • If Mean is good but P95 is high → You still have dangerous hotspots to fix.

Knowledge Nugget: Interpreting the Line Probe

  • Immediate drop behind trees → Highly effective blockage (sharp drop).
  • Gradual slope → Partial blockage, but dust is leaking through.
  • Flat line → Wall is too thin or placed incorrectly.
  • Spike behind wall → Dust is trapped/recirculating in the wake zone.

7) Results Table

WHO guideline display in the pollution analyzer
Scenario Mean (µg/m³) P95 (µg/m³) WHO 2021 Status Line Probe Shape (Post-Trees)
1) No Green Wall
2) With Green Wall (Porous Zone)

8) Discussion Questions

  1. Why must the flow field be stable before accurate PM2.5 analysis can occur?
  2. How could relying solely on the Mean lead to poor health decisions? (Compare to P95).
  3. How did the Green Wall alter the advection path of the dust?
  4. Did the wake zone cause dust to “decrease” or “accumulate”? Why?
  5. Looking at the Line Probe, where did the dust drop the fastest? Does this match the Velocity Map?

Teacher Answer - Discussion Questions

  1. Particle transport uses the velocity field. If the flow is not stable, the advection paths and residence times are still changing, so Mean and P95 values are not repeatable.
  2. The Mean can hide a small high-exposure region. P95 reveals concentrations experienced near the upper end of the spatial or temporal distribution and should be examined with the map, not used as a substitute for it.
  3. The porous wall slows and redistributes the approaching flow, filters or intercepts part of the particle path according to the model, and can redirect the remaining plume around or above the barrier.
  4. A wake can reduce direct transport immediately behind the wall yet accumulate particles in a recirculating pocket. The correct conclusion depends on the local concentration map, residence time, and probe data.
  5. The fastest drop should occur across or immediately behind the effective porous barrier. It should coincide with a velocity reduction, although concentration may rise farther downstream if the wake traps particles.

9) Extension Ideas

10) Grade Level / Indicators

Grade: 10-12 / introductory undergraduate

Indicators:

Subjects:

Lab 7: Wing Walls for Home Ventilation

(2D Top-View Floorplan - Passive Ventilation Design)

Note: Use the 2D Top-View for clear horizontal pathing. This exercise focuses strictly on wind-driven ventilation, ignoring buoyancy.

1) Objectives

Pressure and Wind Direction

Knowledge Nugget: How do Wing Walls work? They act as scoops, catching parallel winds and forcing them inside. They increase local pressure at the window opening, break up skimming flow (wind just sliding past the exterior wall), and force air deeper into the room.

Knowledge Nugget: Why is Passive Ventilation good for tropical climates? It reduces reliance on AC and fans, clears out trapped indoor heat, and increases thermal comfort using zero energy. This is perfect for Thailand’s climate.

3) Key Terminology

For a dimensionless classroom comparison, normalize each ROI speed by the reference inlet speed:

$$ v_i^*=\frac{V_i}{U_{\mathrm{reference}}},\qquad S_D=\frac{100\,\overline{v^*}}{1+0.5\,\sigma_{v^*}^2} $$

If AirSketcher reports a built-in Design Score, record the displayed value and software version. Use the formula above only for an independent classroom calculation; do not mix normalized and raw-velocity scores in one comparison.

4) Simulation Setup

Base Floorplan

5) Equipment / Software

6) Experimental Procedure

Step 1: Load the Floorplan

  1. Open AirSketcher and load/import the residential floorplan file.
Floorplan with Wing Wall

Step 2: Run “With Wing Wall”

  1. Set Wind Speed to 5 m/s.
  2. Click Run.
  3. Wait for residuals to stabilize.
  4. Open Streamlines to observe air entrainment.
  5. Use Line Probe to measure velocity in the ROI.
  6. Record Design Score (from Live Progress View).
  7. Open Qi-Flow and record the metric.
  8. Generate PDF (Analysis and Report).

Step 3: Run “No Wing Wall”

  1. Load the baseline model (or remove the wing wall geometry).
  2. Run again.
  3. Measure the exact same parameters.
  4. Generate PDF.

7) Results Table

Scenario Design Score Avg V (m/s) Variance (σV2) Qi-Flow Harmony Analysis
No Wing Wall
With Wing Wall

8) Data Analysis

Review your recorded data and visually compare the contour maps to answer the core objectives. For a nonzero baseline, calculate the percentage change in Design Score as 100(Swing − Sbase)/Sbase. Compare average velocity and spatial consistency between the two cases. Determine whether the wing wall forced air deeper into the room, then explain the result using windward/leeward pressure and flow-path evidence.

Velocity Comparison

Velocity Comparison

Pressure Comparison

Pressure Comparison

Qi-Flow Comparison

Qi-Flow Comparison

9) Discussion Questions

  1. How does the wing wall increase pressure in front of the window?
  2. Why does a higher Design Score correlate with better human comfort?
  3. If the wing length was changed, how would the results differ?
  4. How can Digital Twins help architects design energy-efficient homes?

Teacher Answer - Discussion Questions

  1. The wing wall creates a windward high-pressure region and redirects part of the external flow toward the opening. The stronger pressure difference across the room drives cross-ventilation.
  2. In this lab, a higher Design Score represents stronger normalized airflow with a penalty for uneven distribution. It is a comparative classroom metric, not a universal comfort standard; temperature, humidity, noise, and occupant preference also matter.
  3. A longer wall may intercept and redirect more flow, but it can also create a larger wake or excessive local speed. A shorter wall may have less capture. Test several lengths with identical inlet and measurement settings.
  4. Digital Twins allow architects to compare layouts, opening positions, and wind directions before construction. They can reduce design iterations and mechanical-cooling demand, but final design still requires climate, thermal, acoustic, structural, and code checks.

10) Extension Ideas

11) Grade Level / Indicators

Lab 8: Lift and Drag Analysis on Airfoil NACA 2412

(Lift-Drag Analysis in 2D CFD)

1) Objectives

2) Fundamental Knowledge

What is NACA 2412?

Because it is a cambered (asymmetrical) airfoil, it can generate Lift even at 0° AoA.

Lift and Drag Equations

$$ L = \frac{1}{2} \rho V^2 C_L A $$

$$ D = \frac{1}{2} \rho V^2 C_D A $$

Where: - L = Lift Force (N)
- D = Drag Force (N)
- ρ = Air density
- V = Velocity
- CL = Lift coefficient
- CD = Drag coefficient
- A = Reference area for a 3D force calculation

For a 2D airfoil, AirSketcher may report force per unit span. With chord c:

$$ L'=\frac{1}{2}\rho V^2C_Lc, \qquad D'=\frac{1}{2}\rho V^2C_Dc, $$

where L′ and D′ are in N/m. Multiplying by an explicitly assumed span b gives L = L′b and D = D′b.

In this lab: - ρ is constant.
- V is constant (20 m/s).
- A is constant.

Changes in force are driven entirely by CL and CD.

Knowledge Nugget: Why do cambered wings lift at 0°?

  • Camber and angle of attack establish a pressure distribution and circulation around the airfoil.
  • In attached flow, lower pressure over much of the upper surface and higher pressure below produce a net upward force.
  • A cambered airfoil can therefore generate positive lift at 0° geometric angle of attack.
  • Cambered wings are great for low-speed flight.

Knowledge Nugget: What is a Stall?

  • Occurs when angle of attack exceeds a critical value; the value depends on Reynolds number, roughness, turbulence, and model settings. A range near 12°-16° may be explored, not assumed.
  • Severe flow separation occurs.
  • A massive wake forms.
  • CL stops increasing and may decrease.
  • CD usually rises sharply.

3) Simulation Setup

4) Equipment / Software

5) Experimental Procedure

Step 1: Prepare the Model

  1. Load the airfoil shape.
Importing an airfoil profile
  1. Set Re = 200, 000 and record the chord, inlet speed, and air properties used by the software.

Step 2: Test Multiple Angles of Attack

Test at: - 0° - 5° - 10° - 15°

For each angle: 1. Rotate the airfoil. 2. Click Run. 3. Open Pressure Contour. 4. Record from Aero Data: - CL - CD - Fy - Fx

Aero data panel in the pressure contour results
  1. Capture Streamline and Pressure images.

6) Results Table

AoA (°) Fy (N/m) Fx (N/m) CL CD L/D Ratio
0
5
10
15

7) Data Analysis

Students should:

  1. Plot CL vs AoA.
  2. Plot CD vs AoA.
  3. Calculate (or record from the software) $L/D = \frac{C_L}{C_D}$.
  4. Identify the Best Glide Angle (max L/D).

Knowledge Nugget: Why does L/D matter?

  • High L/D → Maximum lift for minimum drag.
  • Crucial for glider design.
  • Commercial jets cruise at max L/D to save fuel.

8) Discussion Questions

  1. Why does CL increase as AoA increases initially?
  2. At which AoA did streamline separation (stall) become obvious?
  3. Why does CD rise so rapidly at high AoA?
  4. Which angle provided the highest L/D ratio?
  5. If wind speed is doubled to 40 m/s, how will the forces change?

Calculation note: If ρ, A, CL, and CD remain approximately constant, doubling V multiplies both lift and drag by 22 = 4. If the Reynolds or Mach number change causes the coefficients to change, use the new coefficients instead of assuming an exact factor of four.

Teacher Answer - Discussion Questions

  1. Before stall, increasing angle of attack increases circulation and the pressure difference between the lower and upper surfaces, so CL generally rises.
  2. Stall becomes evident at the first tested angle showing sustained upper-surface separation, a clear wake expansion, and a leveling or decrease in CL. The exact angle must be read from the simulation; it is not fixed by the airfoil name alone.
  3. At high angle of attack, separation enlarges the wake and increases pressure drag. Skin-friction and induced effects may also change, so CD rises rapidly.
  4. The best glide angle is the tested angle with the maximum measured CL/CD, not necessarily the angle with maximum lift.
  5. If ρ, reference area, and coefficients remain constant, doubling speed multiplies lift and drag by four. Recalculate with the new coefficients if Reynolds-number, transition, stall, or compressibility effects change them.

9) Extension Ideas

10) Grade Level / Indicators

Grade: 11

Indicators:

Subjects:

Lab 9: Measuring Airflow with an Orifice Meter

1) Objective

Use AirSketcher to study how an orifice plate measures airflow.

Students will:

2) Basic Idea

An orifice plate is a flat plate with a hole in the center.

When air passes through the smaller opening:

3) Important Equations

Pressure Difference

ΔP = P1 − P2

Where:

Diameter Ratio

$$ \beta=\frac{d}{D} $$

Where:

Orifice Area

$$ A_o=\frac{\pi d^2}{4} $$

Airflow Rate

$$ Q=C_dA_o\sqrt{\frac{2\Delta P}{\rho(1-\beta^4)}} $$

This incompressible, 3D circular-pipe form gives Q in m3/s when SI units are used. For a sharp-edged plate, use an initial classroom estimate of:

The actual discharge coefficient depends on Reynolds number, diameter ratio, plate geometry, and pressure-tap locations. The equation also assumes density change is negligible; keep the flow comfortably subsonic and the pressure difference small relative to absolute pressure.

2D/3D unit check: A planar 2D line probe reports flow per unit depth,

q′ = ∫un dy   [m2/s]

Do not compare q′ directly with the circular-pipe value Q. If the 2D result is interpreted as an extrusion of depth b, then Q = q′b. A planar slit and a circular orifice are different geometries, so label any comparison as a model analogy unless the software uses an axisymmetric or 3D representation.

4) Simulation Setup

  1. Draw a straight air passage.
  2. Add an orifice plate with a hole in the center.
  3. Add a blower before the orifice.
  4. Set the blower direction from left to right.
  5. Run the simulation until the airflow becomes stable.

5) Procedure

  1. Open the Pressure Contour.
  2. Measure the area-averaged static pressure P1 at the specified upstream tap.
  3. Measure the area-averaged static pressure P2 at the specified downstream tap. Keep both tap locations fixed in every run.

  1. Calculate:

ΔP = P1 − P2

  1. Measure the pipe diameter D.
  2. Measure the orifice diameter d.
  3. Calculate β and Ao.
  4. If using a 3D circular-pipe interpretation, use the orifice equation to calculate Q.
  5. Use the Line Probe to obtain q′ from the 2D simulation, or Q if the software explicitly reports a 3D volumetric flow.
  6. Convert to consistent units and geometry before comparing the two results.

Note: In a 2D simulation, m2/s is flow per unit depth. Multiplying by an explicitly assumed depth in metres produces m3/s.

6) Results Table

Measurement Result
Pressure before orifice, P1 (Pa)
Pressure after orifice, P2 (Pa)
Pressure difference, ΔP (Pa)
Pipe diameter, D (m)
Orifice diameter, d (m)
Diameter ratio, β
Orifice area, Ao (m²)
Calculated circular-pipe airflow, Q (m³/s), if applicable
Simulation line-probe flow, q′ (m²/s) or Q (m³/s)
Assumed extrusion depth, b (m), if used

7) Observations

Complete the following sentences:

  1. As air passed through the orifice, its velocity __________.
  2. The pressure at the selected downstream tap was __________ than at the upstream tap.
  3. The calculated airflow was __________ to the simulation airflow.

8) Discussion Questions

  1. Why does air move faster through the orifice?
  2. Why is the pressure lower after the orifice?
  3. Were the calculated and simulated airflow values similar?
  4. What may cause the two airflow values to be different?
  5. What happens to the pressure difference if the orifice hole becomes smaller?

Teacher Answer - Discussion Questions

  1. Continuity requires the flow to accelerate through the smaller opening when the same volumetric flow passes through a reduced area.
  2. Static pressure falls as the flow accelerates toward the restriction. Downstream pressure then recovers only partly because separation, mixing, and viscous losses dissipate mechanical energy.
  3. The values should agree only within the assumptions of the analytical model and after confirming compatible units. Do not compare a 2D line-probe result in m²/s directly with a 3D circular-pipe result in m³/s.
  4. Differences can result from the assumed discharge coefficient, pressure-tap position, mesh resolution, incomplete convergence, compressibility, nonuniform velocity, leakage around the plate, or a 2D/3D geometry mismatch.
  5. For a fixed flow rate, a smaller orifice generally requires a larger pressure difference. For a fixed blower or pressure source, the flow rate may instead decrease. State which boundary condition is held constant.

9) Extension Ideas

10) Conclusion

Write two or three sentences explaining how an orifice meter uses a pressure difference to measure airflow.

11) Grade Level / Indicators

Grade: 11-12

Indicators:

Subjects: Advanced Physics / Fluid Measurement / STEM

Lab 10: Model Scaling and Reynolds Number Similarity

(Scale Input Wind Speed for Wind Tunnel Validation)

1) Objectives

2) Key Terminology

Reynolds number (Re): A dimensionless measure of the ratio of inertial to viscous effects in a flow.

$$ Re=\frac{UL}{\nu} $$

where:

For a prototype and model,

$$ \mathrm{Re}_{\mathrm{real}}=\frac{U_{\mathrm{real}}L_{\mathrm{real}}}{\nu_{\mathrm{real}}}, \qquad \mathrm{Re}_{\mathrm{sim}}=\frac{U_{\mathrm{sim}}L_{\mathrm{sim}}}{\nu_{\mathrm{sim}}}. $$

Matching them gives:

$$ U_{\mathrm{sim}} =U_{\mathrm{real}} \frac{L_{\mathrm{real}}}{L_{\mathrm{sim}}} \frac{\nu_{\mathrm{sim}}}{\nu_{\mathrm{real}}}. $$

If both cases use air at the same kinematic viscosity, this reduces to Usim = Ureal(Lreal/Lsim).

3) Core Concept

Reynolds-number similarity illustration

If a 1:50 scale model uses the full-scale speed and the same fluid, its Reynolds number is only 1/50 of the prototype value. The boundary-layer state, separation, wake, and force coefficients may therefore differ. Increasing model speed can match Reynolds number, but it does not automatically match every relevant similarity parameter.

Validity check: At high model speeds, compressibility and Mach-number effects may become important. If the required speed exceeds the software cap or enters a regime where density change matters, Reynolds-number matching by speed alone is not a valid substitute for a larger model, a different test fluid, or a compressible-flow method.

4) Simulation Setup

5) Equipment / Software

6) Experimental Procedure

  1. Open Expert Options and enable Wind Tunnel Mode.

  2. Draw a simple test object.

    • e.g., A NACA 0012 airfoil (chord ≈ 0.2 m).
    • e.g., A building profile (width ≈ 0.1 m).

  3. Open the Scale Input Wind Speed tool.

    • Click point 1, then point 2 on the canvas to define your characteristic length (Lsim).

  4. In the dialog box, choose ONE scaling mode:

    Mode A: Target Wind Speed (If you know the real-world operational speed).

    • Enter Real Characteristic Length (Lreal) (e.g., real chord = 10 m).
    • Select Target Wind Speed.
    • Enter the real wind speed (e.g., 50 m/s).
    • Note: The tool automatically calculates the necessary Usim to match the real Re.

    Mode B: Target Reynolds Number (Recommended for this lab).

    • Enter Real Characteristic Length (Lreal).
    • Select Target Reynolds Number.
    • Enter desired Re (e.g., 1 × 106 for airfoils, or 2 × 106 for buildings).
    • Click OK. The inlet velocity updates automatically (capped at 500 m/s for stability).
    • Verify the achieved Reynolds number after the cap is applied. If the required speed is above the cap, report that the target was not matched.

  5. Click Run for the Scaled (Re Matched) case.

    • Let residuals converge.
    • Record Streamlines, Pressure, Drag/Lift, and Cd.

  6. Reset the velocity back to a default low speed (e.g., 5 m/s) representing the Unscaled case.

    • Run again.
    • Observe the differences in boundary layer separation and wake size.

  7. Generate PDF reports for both to compare.

7) Results Table

Case Approx Re Inlet U (m/s) Drag or Cd Flow Characteristics (Streamlines) Remarks
Scaled (Re Matched)
Unscaled (Real U)

8) Discussion Questions

  1. Why must Re be equal between a model and the real prototype?
  2. What happened to the separation bubble when the model was left unscaled?
  3. If Lsim = 0.2 m and Lreal = 10 m (1:50 scale), by what factor must velocity increase in Mode A?
  4. How do digital tools like this save engineers time and money in wind tunnel testing?

Teacher Answer - Discussion Questions

  1. Matching Reynolds number preserves the ratio of inertial to viscous effects. This improves similarity of boundary-layer behavior, separation, wake structure, and force coefficients when geometry and other relevant parameters are also similar.
  2. The unmatched model operates at a different Reynolds number, so its separation location and bubble size may differ from the matched case. Students should describe the direction of change from the paired streamline plots rather than assume it.
  3. For the same fluid, Lreal/Lsim = 10/0.2 = 50, so the model speed must be 50 times the real speed. Then verify the software speed cap and keep the Mach number low enough for the incompressible model.
  4. Digital tools allow rapid geometry and parameter changes, repeatable measurements, early screening, and fewer physical prototypes. They reduce iteration cost but do not replace validation, uncertainty analysis, or final wind-tunnel testing when those are required.

9) Extension Ideas

10) Grade Level / Indicators

Grade: 12
Indicators: Sci 3.2 Gr.12/2 (Dimensional Analysis & Similarity)
Subjects: Advanced Physics / Aerodynamics / STEM

Technical References

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