About the very fine mesh near the wall

Leishi · September 17, 2020, 15:30

Dear all,
Recently, I am working on the 2D cycloidal propeller flows using the SST gamma-theta transition model. I put 65 and 75 layers near the wall respectively, resulting in the distance of the first layer to the wall is in order of 10e-8 and 10e-9m. Then, all the results change significantly. (1) the wall shear stress increases dramatically. (2) the velocity profiles on the one side of the foil are also changed. It seems that the mesh is quite fine and the results do not have so much change.Here I attached the two sets of near-wall meshes and corresponding velocity vectors. So, does anybody has some suggestions and comments about that? Very thanks.

ping · September 19, 2020, 02:02

i assume your y+ in the recommended range for that model of 0.1 to 1 in both the mesh cases, but maybe not?

the first case shows a nice velocity gradient where the boundary layer has developed well, whereas the second looks like either early on in the flow field so the b.l. is still developing or the gamma-retheta model has caused the trip to turbulence to create a turbulent b.l. so maybe look upstream for some clues with relevant fields.

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September 19, 2020, 02:02		#2
ping Senior Member Ping Join Date: Mar 2009 Posts: 556 Rep Power: 20	i assume your y+ in the recommended range for that model of 0.1 to 1 in both the mesh cases, but maybe not? the first case shows a nice velocity gradient where the boundary layer has developed well, whereas the second looks like either early on in the flow field so the b.l. is still developing or the gamma-retheta model has caused the trip to turbulence to create a turbulent b.l. so maybe look upstream for some clues with relevant fields.