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About LES+RayleighBernard flow

OpenLB – Open Source Lattice Boltzmann Code Forums on OpenLB General Topics About LES+RayleighBernard flow

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  • #6759

    Hi, I’m trying a high Reynolds non-isothermal flow using LES + Boussinesq approximation,

    I learned the RayleighBernard example case. I think two parts should be modified compared to the example:
    1. the advection lattice descriptor is modified to SmagorinskyAdvectionDiffusionD3Q7Descriptor;
    2. the coupling part should be modified” to “SmagorinskyBoussinesqCouplingGenerator3D”.

    I don’t know whether this is right. So I made the following code. But it does not work. The simulation has been divergent.

    typedef ForcedMRTD3Q19Descriptor NSDESCRIPTOR;
    typedef SmagorinskyAdvectionDiffusionD3Q7Descriptor ADDESCRIPTOR;

    //—————————–Define lattices—————————
    SuperLattice<T, ADDESCRIPTOR> adLattice(superGeometry); // temperature lattice
    SuperLattice<T, NSDESCRIPTOR> nsLattice(superGeometry); // fluid lattice

    T adOmega = converter.getLatticeThermalRelaxationFrequency();
    T nsOmega = converter.getLatticeRelaxationFrequency();

    //———————-Dynamics and boundary conditions————————-
    nsLattice.defineDynamics<SmagorinskyForcedMRTdynamics>(superGeometry, 1);

    //———————-Coupling parts————————-
    std::vector<T> dir{0.0, 0.0, 1.0};
    T boussinesqForcePrefactor = 9.81 / converter.getConversionFactorVelocity() * converter.getConversionFactorTime() * converter.getCharPhysTemperatureDifference() * converter.getPhysThermalExpansionCoefficient();

    T smagoPrefactor = cSmago * cSmago * descriptors::invCs2<T, NSDESCRIPTOR>() * descriptors::invCs2<T, NSDESCRIPTOR>() * 2 * util::sqrt(2);

    SmagorinskyBoussinesqCouplingGenerator3D<T, NSDESCRIPTOR> SmagoCoupling(0, converter.getLatticeLength(lx), 0, converter.getLatticeLength(ly), 0, converter.getLatticeLength(lz), boussinesqForcePrefactor, converter.getLatticeTemperature((Thot – Tcold)/2.0), Thot – Tcold, dir, PrSGS, smagoPrefactor);

    nsLattice.addLatticeCoupling(SmagoCoupling, adLattice);

    //———————Collide and stream parts————————


    I think smagoPrefactor should be around 0.14. For more details . Best Mathias


    Oh, thank you mathias.

    Do you mean that smagoPrefactor in SmagorinskyBoussinesqCouplingGenerator3D is actually the smagorinsky constant, while not smagoPrefactor = cSmago * cSmago * descriptors::invCs2<T, NSDESCRIPTOR>() * descriptors::invCs2<T, NSDESCRIPTOR>() * 2 * util::sqrt(2)?

    By the way, I’m also confused about two parameters deltaTemp and T0 in SmagorinskyBoussinesqCouplingGenerator3D. Should deltaTemp always be 1, meaning I have to normalize the T_high and T_low to 1 and 0? Can I just use the real temperature (like deltaTemp=20℃)? and what is T0? The RayleighBernard example gives the low temperature. Should it always be so? Or is it just a reference temperature that I can set, such as (T_high – T_low)/2?

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