Compressible flow problem

bharath · March 4, 2014, 23:40

Hi to all,
I am simulating a compressible flow with Steam(Equilibirium) in CFX.My input BC's are,

Inlet Total Pressure = 0.05768 atm & T = 308.82 K (mass flow =111.17 kg/s)
Outlet Static Pressure = 0.05004 atm
Reference Pressure = 0 atm

Material: Steam Vapour (IAPWS table).

I started with water ideal gas and it is converged.When switching to steam it is not able start the calculation.
I tried different options and getting different warnings(Invalid number,Floating point, Over flow,High mach number,Table Clipping error and etc..)

Could anybody help me to solve this problem.

Thanks in Advance

ghorrocks · March 5, 2014, 04:24

IAPWS are always hard to converge.

You are using the ideal gas result as an initial condition? That will help a lot.

Also (the standard stuff for numerical instability): Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).

bharath · March 11, 2014, 05:03

Thanks Glenn for your reply.

1) After so many trials i managed to converge 2 cases (Total 5 different Pressure BC cases & Same mesh).But other cases reporting high Mach number and solver is failing.

2) How i can deal this high mach number warning...

ghorrocks · March 11, 2014, 06:21

As I said: Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).

March 4, 2014, 23:40	Compressible flow problem	#1
bharath Senior Member Bharath kumar Join Date: Apr 2009 Posts: 169 Rep Power: 17	Hi to all, I am simulating a compressible flow with Steam(Equilibirium) in CFX.My input BC's are, Inlet Total Pressure = 0.05768 atm & T = 308.82 K (mass flow =111.17 kg/s) Outlet Static Pressure = 0.05004 atm Reference Pressure = 0 atm Material: Steam Vapour (IAPWS table). I started with water ideal gas and it is converged.When switching to steam it is not able start the calculation. I tried different options and getting different warnings(Invalid number,Floating point, Over flow,High mach number,Table Clipping error and etc..) Could anybody help me to solve this problem. Thanks in Advance

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Having Problem solving 2D supersonic flow around a plug nozzle	chrislloyd	FLUENT	7	July 22, 2015 13:09
Problem, adding passive scalar transport for turbulent, compressible flow	cryple	OpenFOAM Programming & Development	2	March 25, 2013 11:00
Boundary condition for compressible flow ( cavity lid problem)	pike@91	Main CFD Forum	2	June 2, 2012 17:04
Negative density problem. compressible flow	Karl	Siemens	2	July 10, 2008 16:41
Problem on boundry of two phase flow	youngan	CFX	0	June 30, 2003 02:32

March 5, 2014, 04:24		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	IAPWS are always hard to converge. You are using the ideal gas result as an initial condition? That will help a lot. Also (the standard stuff for numerical instability): Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).

March 11, 2014, 05:03		#3
bharath Senior Member Bharath kumar Join Date: Apr 2009 Posts: 169 Rep Power: 17	Thanks Glenn for your reply. 1) After so many trials i managed to converge 2 cases (Total 5 different Pressure BC cases & Same mesh).But other cases reporting high Mach number and solver is failing. 2) How i can deal this high mach number warning...

March 11, 2014, 06:21		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	As I said: Improve mesh quality, double precision numerics, smaller time steps, start with low order advection (Upwinding).