grid spacing for supersonic flow

Abhinand · July 25, 2017, 11:08

Hello CFD giants,
Im simualting a supersonic flow over a flat plate with an injector. I know the inlet conditions. How do we calculate the necessary grid spacing in Meshing?.
I went through the Pointwise Calculator and it asks for a desired y+ value.
I cannot understand that. Please help me understand this problem and tell me whether the grid spacing according to Re is essential for simulating 2D and 3D meshes?

Thanks for your time

Kirill-MIPT · July 25, 2017, 14:34

Hello. You may study theory of boundary layer. You will find that it has the same structure if you represent it in special dimensionless coordinates - u+ and y+ (dimensionless velocity and wall spacing). In most supersonic cases using minimum wall spacing that corresponds to y+ = 1 is enough. The main thing is to make sure that distribution of cells provides change between adjacent cells in less than 20%.

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Abhinand · July 26, 2017, 06:59

Thanks for your reply.
So correct me if im wrong, Irrespective of the type of problem, it is necessary to fix a desired y+ value and correspondingly calculate the wall spacing and thereby incorporate into the mesh for better results?
the problem constitutes of viscous flows obviously

Kirill-MIPT · July 26, 2017, 12:49

You are right. Don't forget to implement not too rapid size growth

And for inviscid flow you need to place 20 points (or a bit more) through the shock wave

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July 25, 2017, 11:08	grid spacing for supersonic flow	#1
Abhinand Member Abhinand Join Date: Jun 2016 Posts: 75 Rep Power: 10	Hello CFD giants, Im simualting a supersonic flow over a flat plate with an injector. I know the inlet conditions. How do we calculate the necessary grid spacing in Meshing?. I went through the Pointwise Calculator and it asks for a desired y+ value. I cannot understand that. Please help me understand this problem and tell me whether the grid spacing according to Re is essential for simulating 2D and 3D meshes? Thanks for your time

July 26, 2017, 12:49		#4
Kirill-MIPT Member Kirill Borodin Join Date: Mar 2016 Posts: 60 Rep Power: 10	You are right. Don't forget to implement not too rapid size growth And for inviscid flow you need to place 20 points (or a bit more) through the shock wave Sent from my Redmi Note 3 using CFD Online Forum mobile app Abhinand likes this.

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July 25, 2017, 14:34		#2
Kirill-MIPT Member Kirill Borodin Join Date: Mar 2016 Posts: 60 Rep Power: 10	Hello. You may study theory of boundary layer. You will find that it has the same structure if you represent it in special dimensionless coordinates - u+ and y+ (dimensionless velocity and wall spacing). In most supersonic cases using minimum wall spacing that corresponds to y+ = 1 is enough. The main thing is to make sure that distribution of cells provides change between adjacent cells in less than 20%. Sent from my Redmi Note 3 using CFD Online Forum mobile app

July 26, 2017, 06:59		#3
Abhinand Member Abhinand Join Date: Jun 2016 Posts: 75 Rep Power: 10	Thanks for your reply. So correct me if im wrong, Irrespective of the type of problem, it is necessary to fix a desired y+ value and correspondingly calculate the wall spacing and thereby incorporate into the mesh for better results? the problem constitutes of viscous flows obviously