Pressure below zero

cfdfarmer · July 6, 2015, 01:26

Hello everyone!
I'm suffering from cfd-programming all these days. when I simulating a blunt body with Roe's FDS schemeand some other schemes(Ma=5), the pressure at the wake region often becomes negative,but when there is no wake region, the simulation will be sucessful,how can I cope with the problem?

AshwaniAssam · July 6, 2015, 13:11

May be you need to use some sort of preconditioning. Is it laminar or turbulent flow?

cfdfarmer · July 6, 2015, 23:58

Quote:

Originally Posted by AshwaniAssam

May be you need to use some sort of preconditioning. Is it laminar or turbulent flow?

It's laminar flow.Cound you give me some refrences or articles about preconditioning high speed flow?

Best regards.

AshwaniAssam · July 7, 2015, 12:19

Preconditioning will be little difficult to apply, anyhow reference is here . The reason I asked for laminar or turbulent, is on such high Mach number, your code may need turbulence modelling. Are you validating the code with some reference result.

If yes,
Before going for preconditioning, you can check for your implementation, you can try AUSM+ or SLAU2 scheme which take into account for low speed (then you may not need a preconditioning).
Preconditioning is basically used with a density-based formulation for simulating low Mach number flow, i.e. incompressible flows with desity-based algorithm.

July 6, 2015, 01:26	Pressure below zero	#1
cfdfarmer New Member Join Date: Jul 2015 Posts: 3 Rep Power: 10	Hello everyone! I'm suffering from cfd-programming all these days. when I simulating a blunt body with Roe's FDS schemeand some other schemes(Ma=5), the pressure at the wake region often becomes negative,but when there is no wake region, the simulation will be sucessful,how can I cope with the problem? Last edited by cfdfarmer; July 7, 2015 at 00:15.

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July 6, 2015, 13:11		#2
AshwaniAssam Senior Member Ashwani Join Date: Sep 2013 Location: Hyderabad Posts: 154 Rep Power: 12	May be you need to use some sort of preconditioning. Is it laminar or turbulent flow?

July 7, 2015, 12:19		#4
AshwaniAssam Senior Member Ashwani Join Date: Sep 2013 Location: Hyderabad Posts: 154 Rep Power: 12	Preconditioning will be little difficult to apply, anyhow reference is here . The reason I asked for laminar or turbulent, is on such high Mach number, your code may need turbulence modelling. Are you validating the code with some reference result. If yes, Before going for preconditioning, you can check for your implementation, you can try AUSM+ or SLAU2 scheme which take into account for low speed (then you may not need a preconditioning). Preconditioning is basically used with a density-based formulation for simulating low Mach number flow, i.e. incompressible flows with desity-based algorithm.