Learning Forum

[Aras karimi]

Hello friends,

I am trying to validate the lift and drag coefficients of a symmetrical 3D airfoil. After studying the independence of the solution from the network, I chose the final network and proceeded to obtain the lift and drag coefficients at different angles of attack. Incompressible flow and Re=120,000.

I created the structure mesh with hexahedral elements in ICEM as shown below:

The above network has  Y+<1  and has KW SST turbulence model.

I used the following boundary conditions:

 

Now, after calculating the lift and drag coefficients at different angles of attack, I drew its graphs as follows: (Blue curves)

According to the figure above, the lift coefficient has a very large error compared to the experimental results, while the drag coefficient has a smaller error.

Do you guys think this is a mesh issue or a setup issue?

Thanks in advance

Regards

[Federico]

Hello Aras, 

Cl and Cd will depend on the reference values used to non-dimensionalize the coefficients. You can find those in the Physics tab. Make sure they correspond to your experimental results.

[Aras karimi]

According to the figure below,

in the reference value section, I set the compute frome to the inlet, the Area to the product of the chord length multiplied by the span length, the length to the chord length, and the velocity to the inlet flow speed:

 

Also, in order not to worry about the reference value settings, I once calculated the lift and drag force without setting the reference value part, and the exact same huge error is seen for the lift force:

 

I am very worried and I really don't know what to do. The mesh quality is also very good.

Where do you think the problem could be?

[Aras karimi]

According to the figure below,

in the reference value section, I set the compute frome to the inlet, the Area to the product of the chord length multiplied by the span length, the length to the chord length, and the velocity to the inlet flow speed:

 

Also, in order not to worry about the reference value settings, I once calculated the lift and drag force without setting the reference value part, and the exact same huge error is seen for the lift force:

 

I am very worried and I really don't know what to do. The mesh quality is also very good.

Where do you think the problem could be?

[Federico]

Do you have other data than Cl, Cd from experiment that may help to point at where your results are different?

[Aras karimi]

No, I only have its CL and CD data.