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Minimizing Aerodynamic Drag

Minimizing aerodynamic drag is best done in one of two ways: computational fluid dynamics (CFD, if you use CAD to design the dragster) or a wind tunnel designed for testing scale models, such as Pitsco’s AirTech X-Stream Wind Tunnel, which measures the frontal drag force on your car.

Inside the test chamber of the wind tunnel, the car is held stationary in an air stream. The force of the air pushing back on the car is measured, giving an indication of the car’s aerodynamic efficiency. Lower frontal drag numbers (measured in grams) indicate a higher efficiency of the car’s shape.

By slowing the airspeed and introducing a fog vapor into the air stream, you can visually observe the airflow around your car. Laminar flow, which is a smooth and layered-looking flow, is desirable. Turbulence in the airflow is indicated by eddies, or swirling currents of air, around the car body. Eddies are clearly visible in the wind tunnel.

The presence of eddies indicates that features of your car body are causing aerodynamic drag. Streamlining such features can improve the efficiency of the car’s shape and help it cheat the wind as it moves down the track. The bottom line: more speed!

Choosing a Wind Tunnel

Many aerodynamics concepts such as drag, turbulence, lift, and laminar flow are difficult for students to grasp – wind tunnels give these concepts a visual representation.

Wind tunnels vary in ability, so when looking for one for the classroom, you need to decide whether you want a basic one with a fogger to show laminar flow or you want to be able to measure frontal drag. Also, consider the amount of room available to you, as some wind tunnels can be quite large.

Wind Tunnel Activities

The following wind tunnel activities help to familiarize students with the concepts of aerodynamics and how to use a wind tunnel. Links to the PDF files are below.

If you can’t see the activities when you click the links above, then you’ll need to download Acrobat Reader, a free browser plug-in.

CFD

For those who created their cars in a CAD program, there is the option to test the cars with computational fluid dynamics (CFD), which is a digital way to study the fluid flow around your car, much like a wind tunnel. It creates a computer simulation of how air will flow around the car.

Like CAD, there is an extra learning curve involved with using CFD as well as specialized software. If this is available, it is a good tool to use – many of the TSA Dragster Design winners in recent years have used CFD testing and analysis.