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Pseudo Transient approach

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Old   January 28, 2005, 02:09
Default Pseudo Transient approach
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Xobile
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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,
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Old   January 28, 2005, 17:34
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Piet
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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
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Old   January 28, 2005, 23:41
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Xobile
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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??

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Old   January 29, 2005, 03:13
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sankar
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try reducing residual tolerance for primary variables to avoid this problem
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Old   January 29, 2005, 14:39
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Piet
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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
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Old   February 3, 2013, 05:03
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What is the difference between pseudo transient simulation and transient simulation?
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Old   May 18, 2013, 14:22
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Transient simulation is to solve the problem in time-accurate fashion, while pseudo transient is method to get the steady state solution
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Old   June 30, 2014, 05:19
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Quote:
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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
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Old   February 16, 2018, 05:41
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[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
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Old   February 19, 2018, 15:38
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[QUOTE=adasgupta91;681702]
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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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Old   June 1, 2019, 18:24
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Hi,
I am running a simulation using Pseudo Transient Flow (compressible, turbulent, internal flow). I saw that my residual the became flat very soon. Is that correct?
When I run it normally my residuals go up and down like crazy.
This is my first time running pseudo transient.
Thank you for your help

Denis
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