Solidworks rolling road how-to?

[JJLudemann]

Although this seems like a simple question that needs to be answered for every vehicle simulation, I can't find an answer anywhere on the Internet, even YouTube. I'm using SolidWorks Flow Simulation, and need to know how to properly do the road movement. I've tried several variations with wildly unpredictable results. For example, I ran a 2 element rear wing with sideplates at 150 mph and got downforce of 1442 Newtons. When I put in the road, the downforce went down to 756 Newtons. Obviously, I need to use a boundary condition, but beyond that I've found little but hand waving. My road surface is just a solid box 3m x 7m x 0.01 m. Specifically,

1. Does the road surface need to be contained entirely inside the computation domain, or must it extend outside the domain on the sides?

2. Should the computation domain end at the bottom surface of the road box, or should it extend below, and if so, how far? If I end it below the bottom of the computation domain I get a boundary condition warning.

3. Is the boundary condition applied to only the top surface of the road box, or the top and bottom, or to all surfaces?

Any help would be greatly appreciated.

-Jim

[Wright D]

You should be able to set up a moving wall on any planer surface...give me a call and I can walk you through it. 623.238.0593

[JJLudemann]

I got through to Dustin on the phone, and here's the upshot:

The road surface should extend outside the computation domain on the front, rear, and both sides. The top and bottom faces are given a "real wall" boundary condition of the same velocity in the same direction as the main flow. Be careful that the direction is the same, as the default may be to use the local axes on the road surface instead of the global axes, which may be different by 90 degrees. In my current simulation, the road surface is now just 1mm thick and the computation domain extends only 9mm below that. This seems to be working, as when I look at flow trajectories and pressures on the bottom of the road plate, everything is perfectly straight and constant.

To get correct results for overall lift and drag I had to add a "Surface Parameters" result, in which I used click & drag to select all surfaces except the road. Then I click "evaluate" and when it's finished click the "integral" tab to see the overall lift and drag numbers, shown as Force X and Force Y in my case. On my version of SolidWorks the path to Excel templates are messed up, having a double slash in the middle, and since I can't find a way to change this I get no Excel output. Do not use the "Goals" output of "X Component of Force" and "Y Component of Force" as these include the forces on the road surface and are nearly meaningless.

Apparently meshing is a big concern, and must be done properly to get the correct pressure between the bottom of the car and the road. I haven't tested this out yet.

Thanks, Dustin. ApexSpeed is great!

-Jim