Hello everyone;
I am having a problem with understanding and implementing the Multi relaxation time into my model. As I understand, the MRT is used to stabilize the numerical model when the relaxation time is close to 0.5. I used the example " externalFlowAroundObstacle" in Palabos to try. When the kinematic viscosity is 1E-3, the relaxation time is larger than 0.5, the numerical model ran normally. However, when I reduced the kinematic viscosity leading to the reduction in relaxation time (tau is 0.502), the simulation ran for a while then stopped. I tried to replace BGKdynamics to MRTdynamics but the simulation still ran for a while and then stopped. Therefore, I am not sure, is it because my relaxation time is so low, that even applying MRT cannot stable the simulation. Or I did something wrong so that I cannot stable the model. Or are there any other ways to approach when the relaxation time is low?
Thank you for your time
Hello,
it is very difficult to give you an answer with so little information.
Even if MRT make things better than BGK it cannot solve all stability issues. You could try the CompleteRegularizedBGKdynamics to see if things get better.
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Hi @orestis,
Is there a place where we can read more about this model that you mention, and the other ones implemented in Palabos?
Thanks in advance.
Best,
Javier.
The model I mentioned is this one: https://arxiv.org/abs/1505.06900 The rest is a collection of a lot of other models. For examples the MRT is based on the work of d’Humières, Lallemand, and Luo. There are several papers on the topic.