Adjustable timestep for settleling, then fixed timestep large eddy simulation

stud-many · June 15, 2021, 10:36

I am running LES and URANS simulations in openFOAM. It is essential to settle the simulations fast and then to average with a courant-number < 1 (for the LES). The timestep has to be fixed in order to gain turbulence-data which can be used in FFT.

Is it possible to use an adjustable timestep based on the courant-number first and then define a fixed timestep based on the average timestep used in the first simulation interval?

Rvadrabade · June 16, 2021, 00:09

If I understood requirements correctly,then probably changing 'adjustTimeStep' to 'no' should work, if solver support it. However, you have to calculate average delltaT, probably on your own. You can change this variable value anytime during simulation in controlDict and restart simulation.
Also, it is difficult or tricky to maintain courant number<1 with fixed time step.

June 15, 2021, 10:36	Adjustable timestep for settleling, then fixed timestep large eddy simulation	#1
stud-many New Member Malte Join Date: Nov 2017 Posts: 20 Rep Power: 9	I am running LES and URANS simulations in openFOAM. It is essential to settle the simulations fast and then to average with a courant-number < 1 (for the LES). The timestep has to be fixed in order to gain turbulence-data which can be used in FFT. Is it possible to use an adjustable timestep based on the courant-number first and then define a fixed timestep based on the average timestep used in the first simulation interval?

June 16, 2021, 00:09	Set' adjustTimeStep' to 'no'	#2
Rvadrabade Member Rahul Vadrabade Join Date: Apr 2018 Posts: 46 Rep Power: 8	If I understood requirements correctly,then probably changing 'adjustTimeStep' to 'no' should work, if solver support it. However, you have to calculate average delltaT, probably on your own. You can change this variable value anytime during simulation in controlDict and restart simulation. Also, it is difficult or tricky to maintain courant number<1 with fixed time step.

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