Steady State vs Unsteady

Zaktatir · November 21, 2013, 12:47

Hi,

I am modelling Critical Heat Flux with the RPI-CHF model.

I ran the simulation first of all steady since the results (exp.) turn to be steady.

Now I tried to run it in unsteady manner, however till know in vain.

From increasing/decreasing the time step till using the result of the steady solution did not help.

I am now investigation how much does the steady solver dampens the instabilities in a simulation.

have you noticed somethink like this? The results of the steady solver are compared to exp and showed good agreement (Temperatures/Heat Fluxes and Void are very good)

Thanks

camiliar · February 14, 2014, 20:07

Quote:

Originally Posted by Zaktatir

Hi,

I am modelling Critical Heat Flux with the RPI-CHF model.

I ran the simulation first of all steady since the results (exp.) turn to be steady.

Now I tried to run it in unsteady manner, however till know in vain.

From increasing/decreasing the time step till using the result of the steady solution did not help.

I am now investigation how much does the steady solver dampens the instabilities in a simulation.

have you noticed somethink like this? The results of the steady solver are compared to exp and showed good agreement (Temperatures/Heat Fluxes and Void are very good)

Thanks

hello,Zaktatir
i tried to modelling Critical Heat Flux with the CHF model months ago,and I have some questions about it,that is the critical heat flux model in fluent 14.0,and I tried to do the test case of the CHF model,and I created the physical model of Hoyer,and I set up of this case ,but the result of the calculation is always diverge, and the wall temperature soaring situation does not appear,the highest value of vapor volume fraction is just 0.72. I have tried two months to solve this issue and I’m failed,so will you give me some advises of this problem？thanks

eliastorca · May 11, 2016, 05:00

Hello Camiliar,

I'm simulating the phase change of a refrigerant inside a flowing tube and I'm facing lot of problems. But in your case, it seems to me that you must not use the CHF model, but instead you must use the RPI model as the highest volume fraction is 0.72 (below 0.8, the limit to use the non equilibrium model, and below 0.9, the limit to use the CHF model)

November 21, 2013, 12:47	Steady State vs Unsteady	#1
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	Hi, I am modelling Critical Heat Flux with the RPI-CHF model. I ran the simulation first of all steady since the results (exp.) turn to be steady. Now I tried to run it in unsteady manner, however till know in vain. From increasing/decreasing the time step till using the result of the steady solution did not help. I am now investigation how much does the steady solver dampens the instabilities in a simulation. have you noticed somethink like this? The results of the steady solver are compared to exp and showed good agreement (Temperatures/Heat Fluxes and Void are very good) Thanks

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May 11, 2016, 05:00		#3
eliastorca New Member Elias Join Date: May 2012 Posts: 10 Rep Power: 13	Hello Camiliar, I'm simulating the phase change of a refrigerant inside a flowing tube and I'm facing lot of problems. But in your case, it seems to me that you must not use the CHF model, but instead you must use the RPI model as the highest volume fraction is 0.72 (below 0.8, the limit to use the non equilibrium model, and below 0.9, the limit to use the CHF model)