Slow convergence using stagnation inlet

pad · May 14, 2009, 04:21

Hello,

I am using Star-CCM+ to estimate the mass flow through a valve using a known pressure drop across the valve unit. My plan was to use a stagnation inlet where I specify pressure and a pressure outlet set to 0 Pa.

My problem is that the solution converges very slowly and the first couple of hundred iterations the flow is actually going from low to high pressure before it turns.

I have tried specifying a mass flow at the inlet and the solution converges in less than 60 iterations but since the mass flow is one of the unknown this approach isn't working. Using mass flow at the inlet to obtain an initial guess doesn't work as the flow field still reverses.

Can anyone tell me why the flow is moving opposite of the final flow field when I am specifying pressure at both inlet and outlet? And does anyone know a solution to this...

Regards,
Per

SKK · May 15, 2009, 05:42

We had a similar problem with reverse flow when stagnation pressure was applied to both inlet and outlet, and were told by support engineers that this is a bug in STAR CCM+. That was in one of the v3.0... of STAR CCM+.

pad · May 27, 2009, 06:17

Well, I think I found a solution to this problem.

If I use the URF ramp option and let the factors for both velocity and pressure be very low (e.g. 0.1 and 0.01) for the first 5 iterations and then ramp up to default values the reverse flow problem seems to have disappeared.

May 14, 2009, 04:21	Slow convergence using stagnation inlet	#1
pad New Member PA Join Date: Mar 2009 Posts: 25 Rep Power: 17	Hello, I am using Star-CCM+ to estimate the mass flow through a valve using a known pressure drop across the valve unit. My plan was to use a stagnation inlet where I specify pressure and a pressure outlet set to 0 Pa. My problem is that the solution converges very slowly and the first couple of hundred iterations the flow is actually going from low to high pressure before it turns. I have tried specifying a mass flow at the inlet and the solution converges in less than 60 iterations but since the mass flow is one of the unknown this approach isn't working. Using mass flow at the inlet to obtain an initial guess doesn't work as the flow field still reverses. Can anyone tell me why the flow is moving opposite of the final flow field when I am specifying pressure at both inlet and outlet? And does anyone know a solution to this... Regards, Per ruikeradity1 likes this.

May 27, 2009, 06:17		#3
pad New Member PA Join Date: Mar 2009 Posts: 25 Rep Power: 17	Well, I think I found a solution to this problem. If I use the URF ramp option and let the factors for both velocity and pressure be very low (e.g. 0.1 and 0.01) for the first 5 iterations and then ramp up to default values the reverse flow problem seems to have disappeared. salaisargunansp@gmail.com and ruikeradity1 like this.

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May 15, 2009, 05:42		#2
SKK Member Join Date: Mar 2009 Posts: 55 Rep Power: 17	We had a similar problem with reverse flow when stagnation pressure was applied to both inlet and outlet, and were told by support engineers that this is a bug in STAR CCM+. That was in one of the v3.0... of STAR CCM+.