Sunday, August 5, 2012

Wind Tunnel

A few hours after hearing about the CO2 car contest I found myself in my basement determining if I had all the parts to build a wind tunnel. I made a quick BOM (bill of materials) and decided that I didn't have everything I needed to build a wind tunnel. But then I wondered, are the aerodynamic effects of the car significant? I figured that the main parameters influencing the speed of the car were roughly in order were:

  • Mass 
  • Bearings/Wheel friction
  • Wheel inertia
  • Eyelet friction
  • General axle and cartridge Alignment
  • Aerodynamic
Of course as the mass of the vehicle becomes lighter, the overall velocity in increased causing the aerodynamics to become more important perhaps becoming a little less important than bearing/wheel friction. So why should I spend lots of time making physical models with different shapes to test in a wind tunnel that I hadn't built yet? I decided against building a wind tunnel and choose that if I had enough spare time I would look at what CFD (Computational Fluid Dynamics) models I could generate that would provide the same information without having to build physical models.

I looked around and determined that a few free open source suites, including openFOAM were up to the task.  However I took stock of my skill and found that is was going to take me quiet a while to polish my skill set to feel like I was getting any sort of realist results from the software.

I later found a virtual wind tunnel program in the Autodesk Labs, Project Falcon. This piece of software provides a CFD results for testing body shapes for cars, motorcycles etc. with only a STL triangulated model and a few model parameters.

So I wiped up some simple body shapes in my CAD software an gave it a whirl. Now, I don't expect that the project Falcon is providing my results that are even within 20% of reality, But it did give me a method to compare the relative differences between the designs.

I made many digital models and came up with some general ideas of what the car should be shaped like.

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