About LES+RayleighBernard flow

[steed188]

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);
nsLattice.setParameter<collision::LES::Smagorinsky>(cSmago);
……
adLattice.defineDynamics<AdvectionDiffusionBGKdynamics>(allIndicator);
……
adLattice.setParameter<descriptors::OMEGA>(adOmega);
nsLattice.setParameter<descriptors::OMEGA>(nsOmega);

//———————-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————————
adLattice.collideAndStream();
nsLattice.collideAndStream();
nsLattice.executeCoupling();
//———————————————————————–

[mathias]

I think smagoPrefactor should be around 0.14. For more details https://publikationen.bibliothek.kit.edu/1000126904 . Best Mathias

[steed188]

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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