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Airfoil CFD in COMSOL / issues

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Old   June 17, 2015, 05:33
Default Airfoil CFD in COMSOL / issues
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xenofon kalogeropoulos
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Dear all,

I am in the process of doing a study of double staggered airfoils in Comsol 4.4. Before starting to analyze double airfoils I though it would be good to validate a single airfoil model against XFoil and experimental data. My goal is to run CL/CD predictions in a reasonable AoA range, say 0-10 degrees. Let me walk you through my setup of this study:

- Re = 1x10e6
- Airfoil: SG6043, with 1m chord length
- Fluid Domain: C-domain, radius of 5 chords and downstream length of 10 chords
- Turbulence model: SST
- Boundary layer setup: Yplus ~1 with 20 layers and first layer height calculated as 2.3e-5 m, stretching = 1.3 (see attached images)
- Inlet turbulence variables: Intensity = 0.1%, Length scale = 0.001m

As of yesterday, my best results so far (Comparing to XFoil results are):
Lift: Maximum error: 11%, this is reasonable but should be reduced a bit more.
Drag: Maximum error: 27% (over-prediction), I know drag is extremely difficult to predict accurately due to various effects including possible laminar-to-turbulent transition inside the BL, but the error should be decreased further for my analysis to become reliable at this stage.

I think the most important factor here would be to fix my mesh to be as solid as possible to capture fully the viscous effects that dictate drag. So your advice regarding my mesh (or any other advice indeed) would be extremely helpful.

My first thoughts is that something is not quite right with the leading edge (see images) because the BL mesh is very distorted there. After the solver has done its job, the wall resolution plot shows very high values there, so my effective Yplus at the leading edge's area is much higher than the desired value of 1.

Thanks for your time and effort guys, your feedback will be greatly appreciated!

Best Regards
Xenon



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aerodynamics, aerofoil, airfoil, cfd, wind turbine

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