# Transient parameters for vehicle aerodynamics

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September 27, 2019, 10:33
Transient parameters for vehicle aerodynamics
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Hello everyone!

Im very new in CFD. Currently I am doing external aerodynamics analysis of 3D car model for a university project work. I verified Ahmed Body with around 5% error for the 25 degrees with realizable K-e model (huge thanks to https://www.youtube.com/user/eoescipy - very detailed step by step guide).
My intention, however is to capture the rotating effects of wheel rims, which I recently found out, requires me to do a sliding mesh approach -hence a transient simulation. Now I have next to zero idea about how to set up transient parameters like time step size, no. of time steps etc. And unfortunately I dont have enough time to learn about transient simulation from scratch - I have to show some progress to my project supervisor.

So basically what Im asking is that - what are considered good practices for setting up transient parameters for external aerodynamics in particular such as time step sizes, no. of timesteps, max iterations etc. I need a range of values for them to work on immediately. I understand that I am sounding lazy, but I am so time constrained right now that I simply dont have the time to experiment with transient parameters - which is why Im asking for help. Any kind of tips would be greatly appreciated.

Im describing my method as much as possible-

Turbulence model- realizable k-e NWF

Inflation - First Aspect Ratio 5, 5 layers (y+ around 100-120)
Solution methods, Solution Controls - Please see attached screenshots. I modified the relaxation factors according to the video.

Mesh is very similar to the meshing in the given youtube channel, which meshes the Ahmed body . I will just switch out Ahmed body with my car.

Once again, Im really in trouble right now- and I will greatly appreciate any kind of help. Thank you!
Attached Images
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 Tags fluent, transient 3d, vehicle aerodynamics