# Human Powered Vehicle Study

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 March 2, 2010, 09:29 Human Powered Vehicle Study #1 New Member   Join Date: Dec 2009 Posts: 25 Rep Power: 9 Hi, I am currently conducting an investigation into the aerodynamics of a human powered vehicle such as seen here http://www.speed101.com/photos.htm My aim is too closely match a published figure for a certain HPV of Cd=0.045 I am having some issues currently, my console is giving me limited tubulent viscoscity problems. Could someone please suggest if any of my input conditions seem off? Star CCM+ Sparat Allmaras Model Velocity=32.25 (0 yaw) Turb viscosity ratio=5 or Turb intensity=0.01 (value as seen, this means 1% right?) Length scale 20m (half the domain height) velocity scale = 0.4m/s Im using a trimmer mesh, the object is close to the ground, no rotating wheels. I am using a wind tunnel type domain with slip walls as the far field boundaries. Cheers

 March 2, 2010, 10:50 Turbulent Intensity and Turbulent Length Scale #2 Senior Member     Richard Smith Join Date: Mar 2009 Location: Enfield, NH, USA Posts: 138 Blog Entries: 4 Rep Power: 10 If you are going to use the turbulent intensity and turbulent length scale option then I'd guess (I'm not a Star CMM+ user) that: Turbulent length scale should be a fraction of the vehicle length not the overall domain: http://www.cfd-online.com/Wiki/Turbulence_length_scale Velocity scale (reference?) should be your freestream velocity so that your turbulent intensity can then determine your turbulent velocity fluctuation: http://www.cfd-online.com/Wiki/Turbulence_intensity 0.01 Turbulent intensity = 1%, correct. That's the level you'd expect in a good wind tunnel Matching absolute drag values from experiments is a tough call, just ask the drag workshop: http://aaac.larc.nasa.gov/tsab/cfdlarc/aiaa-dpw/ In my opinion CFD is better suited to computing drag for different designs and using the relative difference (from a baseline) in value to make design decisions. Hope this helps __________________ Symscape, Computational Fluid Dynamics for all

March 2, 2010, 10:54
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 Originally Posted by gocarts If you are going to use the turbulent intensity and turbulent length scale option then I'd guess (I'm not a Star CMM+ user) that: Turbulent length scale should be a fraction of the vehicle length not the overall domain: http://www.cfd-online.com/Wiki/Turbulence_length_scale Velocity scale (reference?) should be your freestream velocity so that your turbulent intensity can then determine your turbulent velocity fluctuation: http://www.cfd-online.com/Wiki/Turbulence_intensity 0.01 Turbulent intensity = 1%, correct. That's the level you'd expect in a good wind tunnel Matching absolute drag values from experiments is a tough call, just ask the drag workshop: http://aaac.larc.nasa.gov/tsab/cfdlarc/aiaa-dpw/ In my opinion CFD is better suited to computing drag for different designs and using the relative difference (from a baseline) in value to make design decisions. Hope this helps
Thanks that re-assures me on a few things.

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