Aerodynamics testing in OpenFoam - Fuel Economy, Hypermiling, EcoModding News and Forum

CarDes · 06-26-2010, 08:09 AM

Hey everyone,

I'm currently working on a car concept (side hobby project). With this specific concept I was hoping to explore the use of a large boat tail for improved aerodynamics. However with the boat tail I am exploring a number of alternate design variations that I have no idea on the aerodynamic properties. (one less odd variation attached)

To test my design I was hoping to use OpenFoam. I have the .stl files ready, it is just a matter of placing it in the OpenFoam simulation of a windtunnel for results (preferably a diagram of the airflow and pressure that I can view in Blender).

Would anyone have any suggestions on what documentation i can follow (or what preset that I can download)?

Any information would be appreciated.

Regards,
Daniel

aerohead · 06-26-2010, 02:51 PM

Quote:

Originally Posted by CarDes

Hey everyone,

I'm currently working on a car concept (side hobby project). With this specific concept I was hoping to explore the use of a large boat tail for improved aerodynamics. However with the boat tail I am exploring a number of alternate design variations that I have no idea on the aerodynamic properties. (one less odd variation attached)

To test my design I was hoping to use OpenFoam. I have the .stl files ready, it is just a matter of placing it in the OpenFoam simulation of a windtunnel for results (preferably a diagram of the airflow and pressure that I can view in Blender).

Would anyone have any suggestions on what documentation i can follow (or what preset that I can download)?

Any information would be appreciated.

Regards,
Daniel

Daniel,I will have to defer to the others which have experience with CFD,as I have never done it,probably won't.
I think that some if not all that are in use,deal only with 2-dimensional inviscid flow about the centerline of the structure and cannot accurately predict the 3-D wake.
Your rendering ( very nice ! ) looks almost like a trike.If it is a three-wheeler,the CFD programs may not work.( about now I'm hoping someone more knowledgeable is tracking this and will correct if necessary ).
Looking at your image,I would suspect that the entire darkly-shaded area behind the lowest character line will be in separation.It might re-attach,can't figure it without a top view.

Diverging flow is the most sensitive to instability and with the short-tail outrigger front fenders I don't believe the flow will be clean enough behind them to allow attached flow beyond that arcing body crease.
Boat-tails won't work if the onset flow coming at them isn't perfect.One really has to on their toes with respect to them.You just can't cheat.
I'll shut up and make room for the whiz kids.
She looks like a fun project,best to you!

CarDes · 07-09-2010, 10:53 AM

Quote:

Originally Posted by aerohead

Daniel,I will have to defer to the others which have experience with CFD,as I have never done it,probably won't.
I think that some if not all that are in use,deal only with 2-dimensional inviscid flow about the centerline of the structure and cannot accurately predict the 3-D wake.
Your rendering ( very nice ! ) looks almost like a trike.If it is a three-wheeler,the CFD programs may not work.( about now I'm hoping someone more knowledgeable is tracking this and will correct if necessary ).
Looking at your image,I would suspect that the entire darkly-shaded area behind the lowest character line will be in separation.It might re-attach,can't figure it without a top view.

Diverging flow is the most sensitive to instability and with the short-tail outrigger front fenders I don't believe the flow will be clean enough behind them to allow attached flow beyond that arcing body crease.
Boat-tails won't work if the onset flow coming at them isn't perfect.One really has to on their toes with respect to them.You just can't cheat.
I'll shut up and make room for the whiz kids.
She looks like a fun project,best to you!

Thanks for your thourough reply Aerohead.

I've been jumping into aerodynamics with a brief understanding of the effect of boat tails without really knowing the basics. It is always good to get good advice to help me produce a solid concept.

Will post final design here when done.

Thanks again,
Daniel

Ardent · 07-09-2010, 01:15 PM

Quote:

Originally Posted by aerohead

I think that some if not all that are in use,deal only with 2-dimensional inviscid flow about the centerline of the structure and cannot accurately predict the 3-D wake.

I'm giving OpenFOAM an initial look myself, but this appears 3D: