Moving fluid vs moving body
 

Hi everybody, I have a question for you:
every time I run a simulation the fluid is moving while the body is still. That means that the situation is similar to the one you would find in a wind tunnel with all it's disadvantages.
So I was thinking about moving the body while the rest of the domain is still. The ground should be a wall if the body is a car and the other domain faces could be simmetry plane or a pressure condition could be imposed on them.

Would it be a good idea? Is there something I'm missing? What do you think?

Thanx


Lorenzo

Lorenzo,

In order to eliminate boundary layer of the ground(wall which is under the car) while flow is moving, I give the ground "velocity inlet" boundary condition with "magnitude and direction" option. Also except symmetry plane and outflow, everywhere is velocity inlet.
By this way, I think I get a good approach like the real world.
Hope it makes sense to you.

Yess, that's what I do as well. I was just wondering which would be the difference between setting a case like you described and setting one like I described.

Hi, I was wondering if somebody else has another explanation.

Moving the body carries the drawback that you need to rebuild the volume mesh in the wake of the vehicle and this comes at a price. You would also need to refine the mesh in front of the vehicle as it passes by.

I agree when we see it as a transient problem with moving boundaries: body moves with respect to control volume and remeshing is needed.

What if we see it as a stationary problem? A body fixed in space with respect to control volume as usual (so no remeshing is needed) with the unusual boundary condition: velocity prescribed on the boundary of the body as movingWallVelocity.

No, that would not work as movingWall is only a surface condition that has an impact on the air that wets the surface. I believe the only case where that would work is a zero thickness flat plate moving parallel to the flow at 0° angle of attack.

I wish I had the time to check this in OpenFOAM: solve two laminar small problems with same mesh: first one with moving fluid and second one with moving body and compare pressure and viscous forces over body.

There are differences, because numerical schemes are not perfect
https://www.google.com/url?sa=t&sour...BhO1xuW13jHUkb