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[janetj]

I am having meshing problem with airfoil having inward dimple. Dimple screenshot is attached. 

https://ibb.co/MVWN7kb
https://ibb.co/bHKDP1R

My structured mesh is poor. I put a circle around the airfoil and generated the mesh, it was okay, but the small area around the dimple is still not okay and the Face Meshing has small blue sign on it suggesting something wrong in the mesh. Please guide.

[peteroznewman]

You need to use much smaller element lengths along the airfoil.

You need to add Inflation Mesh control to the boundary of the airfoil.

[janetj]

Thank you peteroznewman.

After several attempts I was able to get the structured mesh right. However, my solution is not getting converged. In the boundary conditions for inlet, I used components and 1xcosx6 (For x component) and 1xsinx6 for y component. Goes without saying this is for 6 degree angle of attack. My analysis is 2-D steady state and flow is inviscid. 

I tried to find the solution at 1e-3 convergence and I got it. While I tried 1e-6, the convergence is not happening even after 10,000 iterations. 

And as I am simulating individually for different degree alpha, my convergence at 1e-3 was going okay from 0 to 8 degree angle of attack and these are all individual workbench projects for different alphas. Just as I started with 10 degree alpha, I wasn't able to converge the solution even at 1e-3 despite the 10,000 iterations. Why would that be?

Then I read somewhere I should try transient state simulation. I tried that and my solution was converged. May I get a good understanding of how transient state is able to converge my solution and how exactly does the time stepping is performed? 

I guess I should stick to steady state but how to get the solution converged for alphas beyond 8 degree? Please help as this is very important for my project.

Besides, just need a confirmation if I am doing it all right. Once the solution is converged and I obtain the Cl and Cd, say for 6 degree alpha, I enter the following values for Cd: x = 1 cos 6 and y = 1 sin 6. For Cl, I enter, x = 1 sin -6, y = 1 cos -6. And thus I get the Cl and Cd at 6 degree alpha. Velocity is obviously 1m/s here. Am I doing it right?

 

[peteroznewman]

The CFD experts spend time in the Fluid Dynamics category. You should copy this post and start a New Discussion in that category. I am not a CFD expert.

[janetj]

Unable to start a new thread in Fluid Dynamics. This error keeps showing. Weird...

[Rob]

And we've both been on holiday!   

I'm not going to go into depth on airfoil models, but check for flow separation/stall conditions.  If the steady solver struggles and transient works it tends to imply some level of instability in the flow: this can be very difficult to spot but at around 7-8 degrees I'd expect the flow to be trying to separate from the surface.