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December 8, 2019, 11:40 |
FLUENT Scaling - Force Coefficients
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#1 |
New Member
Join Date: Dec 2019
Posts: 13
Rep Power: 7 |
Hi all,
I'm running a 2D thin airfoil simulation in FLUENT which returns force coefficients for lift and drag at 6 degrees AoA with a chord length=1m of CL=0.60 and a Cd=0.018. I've re-run this case (same AoA) with a scaled model (1/4c) and the same Reynolds number (model scaled by a factor of 1/4, therefore free-stream/inlet velocity has been doubled and the kinematic viscosity halved to maintain consistent Re) expecting to return equivalent values for the force coefficients but this hasn't been the case; solution returned CL~0.15 and a Cd~0.0045 which is a quarter of the original solution. As the Re is the same and the mesh has been scaled with the airfoil surface (giving same Y+) I don't understand the reasoning for this or if i've simply made a mistake configuring the sim? Any advisement would be greatly appreciated! Thanks. |
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December 8, 2019, 14:59 |
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#2 |
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,427
Rep Power: 49 |
Did you adjust the reference length to match your scaled model? From the coefficients you obtained, it seems like you forgot to do that.
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December 9, 2019, 09:01 |
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#3 | |
New Member
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Quote:
You're correct that I forgot to adjust the reference length but, having re-run the simulation now, I'm still obtaining the same result(?) |
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December 9, 2019, 09:23 |
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#4 |
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,427
Rep Power: 49 |
I should have been less specific. What I actually meant was "reference values" instead of reference length.
Lift and drag coefficients are calculated using the reference area. Anyway, that's just post-processing. Changing reference values does not change the solution. |
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December 9, 2019, 09:59 |
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#5 | |
New Member
Join Date: Dec 2019
Posts: 13
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Quote:
For this case where I am keeping Re consistent, am I correct in thinking I should expect the same force coefficients (lift / drag)? Thanks again for your help! |
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Tags |
drag coefficient, lift coefficient, reynolds number, scaling |
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