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Relaxation TIme Parameter Limit

OpenLB – Open Source Lattice Boltzmann Code Forums on OpenLB General Topics Relaxation TIme Parameter Limit

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    I am running a micro-structure simulation with my characteristic velocity as 1e-04 m/s and characteristic length as 7.64e-06 m. My delta x for the simulation is 5e-07 m and using BGK collision operator I am calculating the pressure forces at the outlet.My forces are coming out to be in the order of 2e-15 N and the value to which it is comparing has an order of e-14. I tried increasing the tau (relaxation-parameter) from 0.6 to 0.8 to 0.999 and found out that my value is approaching to the reference value. However, in the book The Lattice-Boltzmann Methods by Timm Krüger, it is said that the tau value should not be much greater than 1. So I had the question should I increase my tau to greater than 1 or should I change my collision operator from BGK TO TRT Or MRT operator. Is there any upper limit on the tau value?

    Thanking you in anticipation,



    There is no additional limit on the relaxation time from the implementation side of things and any theoretical considerations translate to the simulation results.

    You can of course try out different collision operators as well as change e.g. the spatial discretization to see what best fits your application.

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