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Xobile January 28, 2005 03:09

Pseudo Transient approach
 
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,

Piet January 28, 2005 18:34

Re: Pseudo Transient approach
 
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

Xobile January 29, 2005 00:41

Re: Pseudo Transient approach
 
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??


sankar January 29, 2005 04:13

Re: Pseudo Transient approach
 
try reducing residual tolerance for primary variables to avoid this problem

Piet January 29, 2005 15:39

Re: Pseudo Transient approach
 
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 06:03

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

Far May 18, 2013 14:22

Transient simulation is to solve the problem in time-accurate fashion, while pseudo transient is method to get the steady state solution

itsme_kit June 30, 2014 05:19

Quote:

Originally Posted by Far (Post 428462)
Transient simulation is to solve the problem in time-accurate fashion, while pseudo transient is method to get the steady state solution

Hi

In what problems, we are recommended to apply pseudo transient method?

Thanks

adasgupta91 February 16, 2018 06:41

[QUOTE=itsme_kit;499259]Hi

In what problems, we are recommended to apply pseudo transient method?

Could someone having experience with pseudo transient method kindly comment when or in which cases does one implement in the soution methods in fluent

LuckyTran February 19, 2018 16:38

[QUOTE=adasgupta91;681702]
Quote:

Originally Posted by itsme_kit (Post 499259)
Hi

In what problems, we are recommended to apply pseudo transient method?

Could someone having experience with pseudo transient method kindly comment when or in which cases does one implement in the soution methods in fluent

The pseudo transient method is an accelerated solver for getting the steady state solution. That means don't apply this for transient problems, only steady state problems. Generally you apply it when you want to get to the solution quicker. Usually this means you have tried SIMPLE and gotten a converged problem but it takes too long. So then maybe you have switch to the COUPLED solver, and here you manage to get a solution slightly quicker but still you want even faster. Then the pseudo-transient solver is a good idea. My recommendation is to start with SIMPLE/COUPLED solvers and only have you have a robust experience with these two solvers (for each problem you are dealing with) then to go to the pseudo transient solver. Accelerating the solution generally leads to oscillatory or unstable solutions so you want to make sure that you have a robust strategy in place first.


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