Oscillating behaviour of variables in a very fine grid

Stuntmanbob · May 4, 2017, 11:56

Hi guys,
i'm simulating the flow around an airfoil of a turbine and had to do a grid convergence study. Therefore i refine my mesh in TRACE, by multiplying the number of nodes in i,j,k-direction by two (finer mesh), and three (finest mesh). So the first mesh has about 2.1 million nodes, the second 16.3 million and the finest about 54.4 million nodes.

When i look at the distribution of the Cp-Value on the blade surface, the finest mesh shows an oscillating behaviour (Screenshot). And so all the other calculated variables, like density.

TRACE uses linear interpolation to set the new points. But the oscillating behaviour can't be seen in the results of the first two mesh, so i think that's not the problem.

Maybe it is a numerical problem? Anyone with ideas?
Thanks in advance and sorry for my bad english.

Greetings,
Stuntmanbob

FMDenaro · May 4, 2017, 12:04

Are you working in double precision? check if the grid refinement over the airfoil is smooth

Stuntmanbob · May 4, 2017, 13:40

Hi,
you're right, the smoothness looks very bad. Thank you very much

Greetings,
Stuntmanbob

May 4, 2017, 12:04		#2
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,849 Rep Power: 73	Are you working in double precision? check if the grid refinement over the airfoil is smooth Stuntmanbob likes this.

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May 4, 2017, 13:40		#3
Stuntmanbob New Member Join Date: May 2015 Posts: 17 Rep Power: 11	Hi, you're right, the smoothness looks very bad. Thank you very much Greetings, Stuntmanbob