Learning Forum

[bianchini.1857628]

Hello, a few days ago I asked help with a mesh, now I have troubles for the validation of a flow around a NACA 4412. I'm trying at 6° but Cl is too low and Cd too high, tried different models and it's the same. Also tried a NACA 0012 with a different type of mesh and it's the same. I'm leaving a few pictures of the mesh and setup. 

Probably I'm doing something wrong. Thanks.

[SRP]

Hi,

I recommend checking the AIC course for more information regarding the airfoil simulation: Flow over an Airfoil - ANSYS Innovation Courses

Thanks

[bianchini.1857628]

Already tried but had no luck. It seems that for 0° AoA I get the correct values, but as soon as I change that I get bad data.

[SRP]

Hi,

Which turbulence simulation model did you use?

Thanks

[bianchini.1857628]

Hi. I intended to use k-w SST, but have also tried k-e and S-A and I get somewhat similar results. Which would be good if they weren't wrong, there has to be something simple I'm missing but can't figure out what.

[SRP]

Hi,

Could you please send the screenshot of the following plot and contours:

1)Residual plot for zero AOA and 6 degree AOA

2)Cl and Cd plot for both AOA

3)Velocity/Pressure contour for both AOA

Thank you

[bianchini.1857628]

Contour at 0°:

Residuals at 0°:

Cl at 0°:

Cd at 0°:

Contour at 6°:

Residuals at 6°:

Cl at 6°:

Cd at 6°:

Changed something in the model and now even the values at 0° are wrong.

[SRP]

Hi,

Can you please uncheck pseudo transient to reduce error and re run simulation once?

Thank you

[bianchini.1857628]

Looks about the same even though convergence is slower.

[SRP]

Hi,

The issue might be with turbulence model and corresponding y+ use to create the inflation layer.

When using low-Re models or any models with enhanced wall treatment, the average Y+ value should be on the order of ~1 to ensure we are capturing the laminar sub-layer. When using wall function models, the Y+ value should ideally be above 15 to avoid erroneous modelling in the buffer layer and the laminar sub-layer. High quality numerical results for the boundary layer will only be obtained if the overall resolution of the boundary layer is sufficient. 

I suggest to please check the y+ corresponding to the turbulence model used.

you can also create an additional variable for the eddy viscosity ratio. Then by plotting this variable , and superimposing mesh in the near-wall region, we can visualize the boundary layer resolution.

Thank you

[bianchini.1857628]

Hi, I figured it out. I changed the walls condition from specified shear stress equal to zero and set it as velocity inlet. Of course I had to change how I defined the velocity, had to use magnitude and direction. Not sure sure what to make of it but results are consistent. Thanks for your help.

[ikacar]

Hi,

The area in the "Reference values" is 1 m2 as default. However, you need to enter "the projection area" coming from Cd or CL formulas. You can easily calculate using the tool below.