rhoPimpleFoam Excessive Courant Numbers and Small Time Steps

mlsk · January 17, 2024, 05:03

Dear CFD-Online community,

I hope this message finds you well. I am currently working on a transient heat transfer simulation using OpenFOAM. The simulation involves a transonic flow over an airfoil, and I am facing challenges related to excessive Courant numbers leading to extremely small time steps.

I have attempted the following troubleshooting steps:
1. Adjusted numerical parameters in the fvSchemes and fvSolution files.
2. Checked and modified boundary conditions where necessary.
3. Reviewed and adjusted relaxation factors in the fvSolution file.
4. Verified mesh quality and refined where needed.

Despite these efforts, the simulation's deltaT has reached an extremely small value (e.g., 2.7686277e-47), causing the simulation to stop. The Courant Number mean is within acceptable limits, but the pressure and time step issues persist.

I would greatly appreciate any guidance or insights from the community on how to address these challenges. Specifically, any suggestions regarding adjusting numerical parameters, modifying boundary conditions, or optimizing the simulation setup would be immensely helpful.

Thank you in advance for your time and expertise.

Best regards,
MLSK

tas38 · January 18, 2024, 14:47

My first suggestion would be to run the transonic flow case as steady-state first if possible. What in the model setup necessitates a transient analysis?

mlsk · February 7, 2024, 00:24

I want to validate Rhopimplefoam in openfoam in transonic case and chose to run simulation of RAE2822 at M=0.7.., Re= 6.5 mil , whose experimnetal data is avalilable on NASA website. inital mesh didn't give matching rsults and saw wave fluctuations in upper surface of airfoil. so i made finer mesh to improve y+ but this simualtion is not going any furhter as delta T is very low.

January 17, 2024, 05:03	rhoPimpleFoam Excessive Courant Numbers and Small Time Steps	#1
mlsk New Member Lakshmi siva kumar Join Date: Aug 2023 Posts: 3 Rep Power: 2	Dear CFD-Online community, I hope this message finds you well. I am currently working on a transient heat transfer simulation using OpenFOAM. The simulation involves a transonic flow over an airfoil, and I am facing challenges related to excessive Courant numbers leading to extremely small time steps. I have attempted the following troubleshooting steps: 1. Adjusted numerical parameters in the fvSchemes and fvSolution files. 2. Checked and modified boundary conditions where necessary. 3. Reviewed and adjusted relaxation factors in the fvSolution file. 4. Verified mesh quality and refined where needed. Despite these efforts, the simulation's deltaT has reached an extremely small value (e.g., 2.7686277e-47), causing the simulation to stop. The Courant Number mean is within acceptable limits, but the pressure and time step issues persist. I would greatly appreciate any guidance or insights from the community on how to address these challenges. Specifically, any suggestions regarding adjusting numerical parameters, modifying boundary conditions, or optimizing the simulation setup would be immensely helpful. Thank you in advance for your time and expertise. Best regards, MLSK

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
The initial transient part of the solution takes too long to fade	Ashkan Kashani	CFX	3	January 28, 2023 18:52
Very low Courant numbers for multiple AMI	usr0830	OpenFOAM Running, Solving & CFD	4	July 24, 2021 08:03
Compressible flows with larger Courant numbers	Tobi	OpenFOAM Running, Solving & CFD	5	February 26, 2021 15:20
pimpleFoam, rhoPimpleFoam unstable at small Courant numbers (time-steps)	peob	OpenFOAM Running, Solving & CFD	18	November 13, 2020 13:56
InterFoam negative alpha	karasa03	OpenFOAM	7	December 12, 2013 03:41

January 18, 2024, 14:47		#2
tas38 Senior Member Troy Snyder Join Date: Jul 2009 Location: Akron, OH Posts: 219 Rep Power: 18	My first suggestion would be to run the transonic flow case as steady-state first if possible. What in the model setup necessitates a transient analysis?

February 7, 2024, 00:24		#3
mlsk New Member Lakshmi siva kumar Join Date: Aug 2023 Posts: 3 Rep Power: 2	I want to validate Rhopimplefoam in openfoam in transonic case and chose to run simulation of RAE2822 at M=0.7.., Re= 6.5 mil , whose experimnetal data is avalilable on NASA website. inital mesh didn't give matching rsults and saw wave fluctuations in upper surface of airfoil. so i made finer mesh to improve y+ but this simualtion is not going any furhter as delta T is very low.