# Dual time stepping for high Mach flows

**URL:** <https://pyfr.discourse.group/t/dual-time-stepping-for-high-mach-flows/1244>\
**Category:** Cases\
**Tags:** compressible\
**Created:** [23 March 2025 12:26 UTC](https://pyfr.discourse.group/t/dual-time-stepping-for-high-mach-flows/1244 "2025-03-23T12:26:03Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Olaf](https://avatars.discourse-cdn.com/v4/letter/o/73ab20/32.png) [@Olaf](https://pyfr.discourse.group/u/Olaf)\
**Post date:** [23 March 2025 12:26 UTC](https://pyfr.discourse.group/t/dual-time-stepping-for-high-mach-flows/1244/1 "2025-03-23T12:26:03Z")

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Hello.

I am trying to use dual time stepping for a compressible flow simulation (M = 5) but I always get the same error no matter what mesh I use. I have tried using the test example but I get the same error over and over again.

This is what the pseudostast.csv and the residual.csv look like.

 ![image](https://global.discourse-cdn.com/free1/uploads/pyfr/original/1X/3b6a4abdc03cff296a4b9ee7a3b814325d9cf0ea.png)  
 ![image](https://global.discourse-cdn.com/free1/uploads/pyfr/original/1X/d56777061259ad1ebcfec5559bd0c90cd4f09ee2.png)

This is the error I get.

 ![image](https://global.discourse-cdn.com/free1/uploads/pyfr/original/1X/aa65191f623289aa52a2f38185b68b317bddc75e.png)

This is the configuration I am trying to use.

 ![image](https://global.discourse-cdn.com/free1/uploads/pyfr/original/1X/da860f27a51d04d51ee0972e86d98d6268d40013.png)

Thanks for the help.

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**Author:** ![p.vincent](https://yyz2.discourse-cdn.com/free1/user_avatar/pyfr.discourse.group/p.vincent/32/225_2.png) [@p.vincent](https://pyfr.discourse.group/u/p.vincent)\
**Post date:** [25 March 2025 09:58 UTC](https://pyfr.discourse.group/t/dual-time-stepping-for-high-mach-flows/1244/2 "2025-03-25T09:58:02Z")

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What is the test case. I presume it has shocks? Do you have the entropy based filtering enabled?

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<div class="post-metadata">

**Author:** ![Olaf](https://avatars.discourse-cdn.com/v4/letter/o/73ab20/32.png) [@Olaf](https://pyfr.discourse.group/u/Olaf)\
**Post date:** [5 April 2025 11:16 UTC](https://pyfr.discourse.group/t/dual-time-stepping-for-high-mach-flows/1244/3 "2025-04-05T11:16:55Z")

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I believe entropy filtering is not compatible with dual time step. Tried to run the dual mach reflections.

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**Author:** ![fdw](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@fdw](https://pyfr.discourse.group/u/fdw)\
**Post date:** [7 April 2025 18:42 UTC](https://pyfr.discourse.group/t/dual-time-stepping-for-high-mach-flows/1244/4 "2025-04-07T18:42:02Z")

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To run that case you will need some kind of shock capturing scheme. Of those currently in PyFR entropy filtering is by far the best. Thus, I strongly suggest you switch to explicit time stepping?

Regards, Freddie.