Pseudo Transient approach

January 28, 2005, 02:09

Hello,

does anyone have any tutorial or simulation which uses pseudo transient approach as an initial guess for flow field initialization?

I am running a high speed compressible flow and would really appreciate any help,

January 28, 2005, 17:34

A tutorial what for? Just switch it on, set your time step (in your case 1.E-08) and run it! There's nothing special that could be mentioned in a tutorial!!!

hope this helps

Piet

January 28, 2005, 23:41

when i am running steady state option for high speed compressible flow... it is giving me a converged solution.

But when i run the same case for pseudo-transient case, the simulation stops due to negative densities in more than 100 cells.. of course my time step was 0.1

will decreasing my time step to 1E-8 solve this issue??

January 29, 2005, 03:13

try reducing residual tolerance for primary variables to avoid this problem

January 29, 2005, 14:39

Yes, your are absolutely right. It can solve your problem. Maybe 1.E-8 is not small enough! Try to lower it further for several hundred steps and enhance it from time to time. Any hint for such cases is to start the calculation with a dependency of temperature. This means rho = f(T) and switch back after lets say 100 iterations.

best regards

Piet

crispysalt · February 3, 2013, 05:03

What is the difference between pseudo transient simulation and transient simulation?

January 28, 2005, 02:09	Pseudo Transient approach	#1
Xobile Guest Posts: n/a	Hello, does anyone have any tutorial or simulation which uses pseudo transient approach as an initial guess for flow field initialization? I am running a high speed compressible flow and would really appreciate any help,

January 28, 2005, 17:34	Re: Pseudo Transient approach	#2
Piet Guest Posts: n/a	A tutorial what for? Just switch it on, set your time step (in your case 1.E-08) and run it! There's nothing special that could be mentioned in a tutorial!!! hope this helps Piet

January 28, 2005, 23:41	Re: Pseudo Transient approach	#3
Xobile Guest Posts: n/a	when i am running steady state option for high speed compressible flow... it is giving me a converged solution. But when i run the same case for pseudo-transient case, the simulation stops due to negative densities in more than 100 cells.. of course my time step was 0.1 will decreasing my time step to 1E-8 solve this issue??

January 29, 2005, 03:13	Re: Pseudo Transient approach	#4
sankar Guest Posts: n/a	try reducing residual tolerance for primary variables to avoid this problem

January 29, 2005, 14:39	Re: Pseudo Transient approach	#5
Piet Guest Posts: n/a	Yes, your are absolutely right. It can solve your problem. Maybe 1.E-8 is not small enough! Try to lower it further for several hundred steps and enhance it from time to time. Any hint for such cases is to start the calculation with a dependency of temperature. This means rho = f(T) and switch back after lets say 100 iterations. best regards Piet

February 3, 2013, 05:03		#6
crispysalt New Member Join Date: Dec 2011 Posts: 29 Rep Power: 3	What is the difference between pseudo transient simulation and transient simulation?

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