Learning Forum

[vroomZOOM]

Hello, new fluent user here. One of my course assignments was to model the flow around a NACA 0015 at 12 degrees aoa in fluent, using three different c grid meshes, with both inviscid and viscid (transition k-kl omega) using the density based solver. The coarsest mesh worked just fine for both viscid and inviscid. I then reduced the average cell size by around 1.5, and inviscid worked fine. When I tried to run the viscid, the residuals got stuck in this cycle and would not go down. I tried messing with the courant number (currently set at 5), and tried anything from 0.5 to 50. No dice. I am trying to get the continuity residual below 1e-5.

I tried lowering the URF's for the k, kl, and omega, but that did not help either. I can't seem to find an answer from anywhere online, as most have oscillations, but they change in magnitude, and here, they are exactly the same for 10000+ iterations. I also heard that these oscillations could be indicating convergence of the solution, but when I look at the generated force coefficients, they are steadily increasing with more iterations, so I am not sure if it is really converged here. I attached a picture of the residuals here, hoping someone can help me out. Thanks!

[Rob]

Have a look at the flow field. What's going on?

[vroomZOOM]

not sure if your post was a question or a statement, but here are some pictures of the flow field. I don't see any turbulence or anything that could throw things off by my limited knowledge (only a third year) .

[Rob]

Focus on the low pressure region on the leading edge and look at the velocity vectors. Turbulence tends to be a high frequency oscillation, chances are you're looking at partial flow separation.