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-   -   Vehicle aerodynamics-Flow analysis (http://www.cfd-online.com/Forums/ansys-meshing/120603-vehicle-aerodynamics-flow-analysis.html)

Anand Sis July 10, 2013 11:15

Vehicle aerodynamics-Flow analysis
 
3 Attachment(s)
Hi everyone...
I've been trying to model the flow around a car with an aim to determine the aerodynamic lift and drag induced and the local velocity near the rear of the vehicle(almost at a point where the leading edge of a spoiler will come) to a fair level of accuracy.
I tried to add prism layers around the vehicle body and near the ground...I've attached the screenshot of the settings i gave...plus the rough mesh i got without the prism layers :(
My problem is that am not able to generate the prism layers as ANSYS Meshing seems to freeze after sometime but it doesn't crash :confused:

I've tried running it for hours but its still frozen ...it seems to get stuck at "Modelling interior for part"...
Any reason that anyone might know ?..i don't think its because of my low end system...coz its not using more than 2.5GB of my system memory(I got 8gigs) !

siw July 11, 2013 02:27

Are you using the pre prism generation, rather than the post prism generation? If so you could then preview the prism mesh (before it makes the volume filling tetrahedral elements). This might help in working towards solving your mesh issue. I cannot recall if this works of the first aspect ratio optio but you ould change to smooth transition or first layer height, for instance.

MachZero July 11, 2013 07:20

Ansys meshing is super finicky and super buggy. I have loads of problems with it. What version are you using? V 14.5 was supposed to be worlds better but I noticed in 14.5.7 all sorts if bugs and freeze ups. When I have these issues I delete the meshing cell and start from scratch. Then as I'm rebuilding I has controls one at a time and mesh. This helps to find the problem. It wouldn't surprise me if there was a bug in their code that wasn't happy because you has 3 face sizings in a row. I've had a bug caused by something similar.

By the way, why are you modeling the interior?

Far July 11, 2013 09:04

Try ICEM CFD it is much faster and robust along with Tgrid.

Anand Sis July 11, 2013 12:16

Quote:

Originally Posted by MachZero (Post 439158)
Ansys meshing is super finicky and super buggy. I have loads of problems with it. What version are you using? V 14.5 was supposed to be worlds better but I noticed in 14.5.7 all sorts if bugs and freeze ups. When I have these issues I delete the meshing cell and start from scratch. Then as I'm rebuilding I has controls one at a time and mesh. This helps to find the problem. It wouldn't surprise me if there was a bug in their code that wasn't happy because you has 3 face sizings in a row. I've had a bug caused by something similar.

By the way, why are you modeling the interior?

@MachZero. Am using V14.0 and yes i used 2 face sizings. I had actually followed a video tutorial from youtube where an Ahmed body had been meshed using a similar approach flawlessly. I had considered mine as a simple geometry and assumed it would work. I guess it was not that simple for Ansys meshing after all !! :p
And regarding the interior, i was trying to include the volume of fluid between the wheel arch and the tires as well...i guess that's what u meant ? May be that small volume had been creating problems for me :confused:

ConstantineTheGreat July 11, 2013 12:45

Quote:

Originally Posted by Anand Sis (Post 438993)
I've been trying to model the flow around a car with an aim to determine the aerodynamic lift and drag induced and the local velocity near the rear of the vehicle(almost at a point where the leading edge of a spoiler will come) to a fair level of accuracy.

If you want to simulate the flow around a car why you build a mash inside a vehicle and its wheels?
Try to exclude the interior of the vehicle from the area calculation

Anand Sis July 11, 2013 12:53

Quote:

Originally Posted by ConstantineTheGreat (Post 439230)
If you want to simulate the flow around a car why you build a mash inside a vehicle and its wheels?
Try to exclude the interior of the vehicle from the area calculation

I tried to include the volume of air between the wheel arch and the tires as i sd. The mesh you see doesn't include the entire wheels. That's how it should be..right ?

MachZero July 11, 2013 13:57

I think I misunderstood the image you showed. You have a symmetry model and this is a side view, isn't it? I was under the impression you tried to mesh the volume of the interior of the car. My
Mistake.
One thing I have noticed is that sometimes inflation can't run ansys meshing into the ground as it appears to have done to you. It looks like you have a very fine mesh around the tires. I bet this is where meshing messes up. Please try placing a coarse mesh on the wheel, and all over, then try. If that works you can reduce the mesh size from there

Anand Sis July 22, 2013 06:24

Thanks everyone for your replies. I had found out the cause of the error. It was a problem with my geometry, where the wheels met the bottom surface. The lowest part of the tires had a very small angle between them and the ground,because of which prism layers could not be generated.The solution adopted for this was cutting the lowest part of the tire using design modeler four millimeters over the surface. Then, the tire was extruded on the Z direction(vertical) connecting the tire and the ground and then the prisms could be generated. :)


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