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Vehicle aerodynamics-Flow analysis

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Old   July 10, 2013, 07:09
Post Vehicle aerodynamics-Flow analysis
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Anand
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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...Since am pretty new to CFD, I was wondering how important it is to accurately model the boundary layer near the car body as well as the ground...i have been using a general tetra mesh(with face sizing in the relevant regions) until now and was thinking about introducing a program controlled inflation , to introduce prism layers at these regions
Am using Fluent module in ANSYS Workbench btw
Please give your suggestions and advice
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Old   July 10, 2013, 07:57
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depending on the turbulence model you use, you may need to get y+ less than 1, thus need to generate prism layer near wall. this would make your analysis more accurate, but if you have limited computational power i would suggest you to go with 30<y+<60 and use realizable k-eps with an appropriate wall function. this might work as well.
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Old   July 10, 2013, 08:52
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Thanks @whizkid for your reply
I've been trying 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

I've tried running it for hours but its still frozen ...it seems to get stuck at "Modelling interior for part"...
Any reason that you 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) !
Attached Images
File Type: jpg mesh.jpg (106.0 KB, 43 views)
File Type: jpg ANSYS settings.jpg (52.0 KB, 22 views)
File Type: jpg mesh close.jpg (99.6 KB, 37 views)
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Old   July 10, 2013, 09:25
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in order to calculate aerodynamic coefficients, no need to generate interior grid, i guess... and your problem with generating prism layer, well, i do not use ANSYS meshing, so i cant give you a proper answer, unfortunately.
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Old   July 10, 2013, 11:00
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The interior grid you see is actually on the lateral surface of the car
And i guess i should post my query in ANSYS forum instead
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Old   September 28, 2013, 03:04
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Hi,

You can try using different meshing option available in Ansys to create layers, instead of using First aspect ratio. (second image)

Use first layer thickness option, based upon your calculations define the 1st layer thickness, number of layers required.

Your 1st layer thickness also depends on the turbulence model being used. You start with k-epsilon turbulence model.

Regards,
Chandan
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