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Ground boundary condition low drag vehicle

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Old   November 3, 2020, 06:06
Default Ground boundary condition low drag vehicle
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Hi all ! I am performing aerodynamics simulation on a low drag vehicle.
I have the vehicle in a farfield (parallelepiped). The farfield consists of a velocity inlet, a pressure outlet, a ceiling, side walls and the ground at a specific distance from the vehicle (ground clearance). Having the coordinate system fixed to the car, the air around is moving and hence there is a velocity inlet specified and equal to the velocity of the car. Now, I am not sure what is the correct boundary layer that i should apply on the ground.
I have tried the following:
-ground as moving wall (velocity=velocity inlet) with inflation layer on it (set during meshing)
-ground as moving wall with no inflation layer on it (the ground is set as symmetry in the mesh settings and then in the solution I switched the type to wall and set a velocity on it)
-ground as symmetry

In the first two options, when the ground is set to be a moving wall it is also a no slip wall. This is in my opinion not realistic since in this coordinate frame the ground is moving but no boundary layer is generated on it.
However, the symmetry condition also seems to be not entirely correct since it doesnt imply the ground to move with respect to the car. (if i understood correctly this setting).
Which one of the 3 above is the correct setting in your opinion? I have tried all of them and i obtain significant differences in the drag values.
I have read some papers regarding aerodynamics simulations on racing vehicles in which they set the ground to be a moving wall. However, in my case i really need to be precise in capturing the correct behaviour since it is a low drag vehicle .

Thanks in advance !
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boundary conditions, boundary layer, ground, low drag vehicle, symmetry

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