SimScale CAE Forum

Odd fluid behavior in wind tunnel simulation

I’m working on a CFD simulation to understand the lift distribution and general lift/drag characteristics of a drone.

I’m running a steady-state incompressible simulation with a fixed velocity inlet of 25m/s, a pressure outlet (fixed at 0), a symmetric wall, and 3 slip condition walls. I’ve run this type of simulation successfully many times, however this model is giving me some really odd results for some reason, with the flow moving in ways I cannot explain. Does anyone know what might be the issue.

Most of my residuals and forces are stable, however my inlet plots are oscillating a lot for no reason



![image|690x224]

Here’s a link to the project: https://www.simscale.com/projects/npushp/mvp_cfd_1/

Any help would be greatly appreciated, thanks

Hi,

The domain is definitely too short upstream, on top, on the bottom, and also on the side of the airfoil. It would be a good idea to extend the boundaries further. Figure 8 from this tutorial should give you a good rule of thumb.

Furthermore, enabling “Potential flow initialization” is always a good idea for external aerodynamics (see the image above).

Cheers

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Thanks! I tried those and I’m getting convergence and accurate results now!

I’m not sure which one made all the difference (my guess is moving meshing from the hexagonal mesher to the standard one and handling the inflation/refinement myself), but everything else also helped with accuracy and all.

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