[lovecraft22]

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

[kdrbrk]

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.

[lovecraft22]

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.

[hectorgabriel85]

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

[lovecraft22]

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.

[hectorgabriel85]

Originally Posted by lovecraft22

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.

[lovecraft22]

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.

[hectorgabriel85]

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.

[sbaffini]

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