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Does temperature limiter cause solver blow up ?

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Old   December 22, 2023, 10:11
Default Does temperature limiter cause solver blow up ?
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Adithya Ajay
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I know this is a frequent question in the forum. But...
I am running a supersonic nozzle simulation. To keep my Y+ near 1, I am giving a very small first cell thickness, and cells above these have it,s height gradually increased. Hence my aspect ratios are somewhat high near the outlet.
I am extending my external domain to give accurate boundary conditions. While running density-based simulations, after soo many iterations temperature is getting limited to 5000K which is not possible physically in my case. But since these high temperatures are not in my area of interest I am neglecting it. But after many iterations floating point errors are arising.All mesh parameters are good ( Min orthogonal quality >0.9, Max skewness < 0.2, Aspect ratio max:333 !!!) My doubts are :

1. Are these temperature limits causing the solver to blow up?
2. I am defining convergence based on net mass imbalance (inflow - outflow)/inflow to be less than 1 % even though my residuals are still in the range of 10^-2 or 10^-3 ( they are oscillating at that range). I am also putting markers around the domain at different locations and plotting velocity against iterations. Is this approach okay?

Thank you in advance for the reply.

I am posting the image where AR is high and temperature is getting limited. I only care about the inlet ,not on the external domain !!)
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File Type: png Screenshot 2023-12-22 205107.png (37.3 KB, 6 views)

Last edited by Adithya Ajay; December 22, 2023 at 10:25. Reason: To input more information
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Old   December 22, 2023, 15:44
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Yes limiters can exacerbate some problems. >5000K is not physical but once you apply the limiters, now you have jump conditions and super large gradients in the simulation which are even more unphysical.

For example you might say that the maximum temperature expected in my simulation is 300 K and limit the max temperature to 300 K, thinking it is the "physically correct" thing to do. But do so and your simulation blows up even faster.

Don't worry about addressing the symptoms, fix the problem.
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Old   December 24, 2023, 15:34
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Adithya Ajay
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As you can see my mesh metrics except A.R is okay (I think). What else can I do to avoid this large temperature ?
And what's your opinion about the convergence technique in question
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convergence criteria, floating point error, supersonic internal flows, temperature limited

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