What can a ketchup bottle teach us about computational fluid dynamics? More than you might expect. Understanding how ketchup flows could help engineers explore packaging designs that leave less product behind.
A Small Problem With a Bigger Impact
We’ve all experienced it. A ketchup bottle is nearly empty, but a surprising amount of sauce remains stuck to the inside. Tilting, shaking, or tapping the bottle might help, yet some of the product can still be difficult to remove.
It seems like a minor inconvenience. But when similar losses occur across millions of containers, even small amounts of leftover product can add up to substantial food waste.
In fact, research on tomato ketchup packaging has shown that the amount of product remaining inside a container can influence both its environmental and economic performance.
This raises an interesting engineering question: Could better packaging design help consumers use more of the product they purchase?
One way to investigate this challenge is through Computational Fluid Dynamics (CFD), a numerical simulation approach used to study how fluids move and interact with their surroundings. Although CFD is often associated with aircraft, automotive engineering, and industrial processes, its applications extend to everyday products, including food packaging.
Why Is Ketchup So Difficult to Pour?
To understand how simulation might improve bottle design, we first need to understand the unusual way ketchup behaves.
Unlike water, ketchup is a non-Newtonian fluid. This means its apparent viscosity, or resistance to flow, can change depending on the forces acting on it.
Ketchup typically exhibits shear-thinning behavior: its apparent viscosity decreases as the shear rate increases.
This helps explain why ketchup can remain almost motionless inside a bottle but begin flowing more easily when the bottle is shaken, squeezed, or tapped.
Many ketchup formulations also exhibit yield-stress behavior, meaning a certain level of stress is required before sustained flow begins.
These properties make ketchup more complicated to model than ordinary liquids such as water.
Engineers can use rheological models, including the Power-Law and Herschel–Bulkley models, to approximate these characteristics. The Power-Law model describes shear-thinning behavior, while the Herschel–Bulkley model can also represent yield stress.
However, the most suitable model depends on the actual product formulation and measured material properties. Some ketchup formulations also exhibit time-dependent behavior, which may require more advanced modeling approaches. Understanding these characteristics is essential when predicting how ketchup will move through a container.
How Can CFD Help Improve Bottle Design?
Computational Fluid Dynamics allows engineers to simulate fluid motion and examine how different design choices may influence performance.
For a ketchup bottle, CFD could help investigate several important questions:
- Bottle geometry: How do the shape, shoulders, and internal corners affect the movement of ketchup?
- Neck and outlet design: Could changing the opening improve dispensing and reduce product accumulation?
- Pouring angle: How does tilting the bottle affect drainage and the amount of ketchup remaining?
- Surface properties: How might different internal materials and wetting characteristics influence product retention?
- Fluid behavior: How do viscosity and yield stress affect dispensing time and residual product?
Rather than relying entirely on physical prototypes, engineers can use simulation to compare design alternatives and identify promising configurations for further testing.
For example, a simulation could investigate whether a different transition between the bottle body and neck improves drainage under a specified pouring condition. The objective is not simply to make ketchup flow faster. A successful design also needs to provide controlled dispensing, convenient handling, and practical manufacturing performance.
Tracking Ketchup and Air With the Volume of Fluid Method
Bottle-emptying simulations present another interesting challenge: the interaction between ketchup and the surrounding air.
As ketchup moves out of a container, the position of the ketchup–air interface changes. In a rigid bottle, incoming air can also play an important role in the emptying process.
One established approach for studying this type of flow is the Volume of Fluid (VOF) method.
VOF is a numerical technique used to track the changing interface between different fluid phases, such as liquid and air.
When combined with a suitable model of ketchup’s non-Newtonian behavior, this approach can help engineers investigate how the product moves during dispensing.
Depending on the simulation setup, engineers may be able to evaluate:
- How much ketchup remains after a defined pouring procedure.
- Where product tends to accumulate inside the bottle.
- How quickly the product leaves the container.
- How changes in bottle geometry influence emptying performance.
Accurate predictions also require appropriate treatment of wall interactions, surface tension, and other relevant physical effects. Importantly, simulation results should be compared with experimental measurements. CFD provides a way to investigate design possibilities, but reliable engineering decisions still depend on suitable model assumptions and validation.
From Better Flow to Less Food Waste
The potential value of improved packaging extends beyond convenience.
When a product is manufactured and distributed at scale, reducing the amount left inside each container could contribute to lower food waste.
For consumers, this may mean getting more value from the product they purchase. For manufacturers, it creates opportunities to improve packaging functionality and overall product performance.
However, reducing leftover ketchup is only one part of sustainable packaging design.
Engineers must also consider factors such as material consumption, manufacturing requirements, food safety, and recyclability. A design that improves product recovery is not necessarily more sustainable overall if it introduces other significant environmental impacts. This is where engineering analysis becomes especially valuable. Simulation, experimental testing, and broader environmental assessments can work together to help evaluate design trade-offs.
Everyday Problems, Engineering Opportunities
The ketchup bottle is a useful reminder that engineering challenges are not always large or obvious.
The same principles of fluid mechanics used to study airflow around buildings, flow through industrial equipment, or complex transportation systems can also help us understand the behavior of everyday products.
At Polar Dynamix, we focus on making fluid dynamics and engineering simulation more accessible, understandable, and useful for practical decision-making.
Exploring familiar problems through the lens of CFD helps demonstrate how numerical simulation can support innovation across a wide range of applications.
Whether the goal is improving ventilation, understanding fluid behavior, or investigating smarter product designs, the starting point is often the same: asking the right question and using engineering tools to explore possible answers.
So, how can we design a bottle that leaves less ketchup behind?
It is a simple question with some surprisingly complex fluid mechanics behind it. And it illustrates an important idea: sometimes, meaningful engineering opportunities begin with solving a small problem at a very large scale.
About Polar Dynamix
Polar Dynamix is a technology company dedicated to making engineering simulation more accessible and intuitive. Through our specialized 2D Computational Fluid Dynamics (CFD) software, AirSketcher, we help professionals, educators, and students visualize airflow patterns, explore design concepts, and develop a deeper understanding of fluid dynamics