## Fluids

#### Airfoil Simulation in Ground effect

• oyallou
Subscriber

Hello,

I am performing a 2D airfoil simulation to determine the best angle of attack of the airfoil on the front wing. Since this is going to be in the proximity of the ground, the effects of the ground must be taken into account.

To account for this, I have a moving wall boundary condition set at the ground with the same speed as the inlet.

For my mesh, I have three body of influences:

Small Box near the airfoil: 0.03 m

Large box: 0.08 m

Global Sizing: 0.3 m max face size and 0.001 m min face size

I am using the k-w SST model to capture the flow.

I ran this at the first two airfoil configurations and got all the residuals to drop below 1e-6 except for the continuity. I do not know why this is. However, when I move to the higher angles of attack, I get oscillating plots for the drag and lift coefficients and the residuals won't drop past their initial values.

Does anyone know why this is? Does anyone have any experience with modeling airfoils in ground effect that could offer some advice about these simulations?

Thank you

• Raef.Kobeissi
Subscriber
What is the velocity used? And what is your residual error of your continuity? It is not a rule to have all equations reaching same residuals. Even if continuity has anhigher residual error that doesnt mean it hasnt converged.

Regards
• oyallou
Subscriber

The speed is 28 m/s. The chord length is 500 mm. The continuity residual is at roughly 2e-4. I check the mass imbalance plot and the location of variation in the residuals is far enough away from the airfoil that I can okay with it.

Do you have any idea why the residuals for higher angles of attack does not work and do not drop?

Thank you

• Raef.Kobeissi
Subscriber
Did you tey to reduce your under-relaxation factor for the continuity equation from 0.7 (Default) to 0.55? What is your ultimate goal for the residual error? 1e-4?