channel3d Taueff

[liu]

Dear OpenLB community,
I would like to ask in which function is the effective relaxation time of Taueff calculated in the case of channel3d, thank you very much

[liu]

namespace detail {

template <typename COLLISION, typename DESCRIPTOR, typename MOMENTA, typename EQUILIBRIUM>
struct SmagorinskyEffectiveOmega {
using MomentaF = typename MOMENTA::template type<DESCRIPTOR>;
using CollisionO = typename COLLISION::template type<DESCRIPTOR, MOMENTA, EQUILIBRIUM>;

template <typename CELL, typename PARAMETERS, typename V=typename CELL::value_t>
V computeEffectiveOmega(CELL& cell, PARAMETERS& parameters) any_platform {
V piNeqNormSqr { };
MomentaF().computePiNeqNormSqr(cell, piNeqNormSqr);
const V rho = MomentaF().computeRho(cell);
const V omega = parameters.template get<descriptors::OMEGA>();
std::cout << “omega1111111: ” << parameters.template get<descriptors::OMEGA>() << std::endl;
const V smagorinsky = parameters.template get<collision::LES::Smagorinsky>();
V piNeqNorm = util::sqrt(piNeqNormSqr);
V preFactor = smagorinsky*smagorinsky
* descriptors::invCs2<V,DESCRIPTOR>()*descriptors::invCs2<V,DESCRIPTOR>()
* 2 * util::sqrt(2);
/// Molecular realaxation time
V tauMol = V{1} / omega;

std::cout << “tauMol: ” << tauMol << std::endl << std::flush;
/// Turbulent realaxation time
V tauTurb = V{0.5} * (util::sqrt(tauMol*tauMol + preFactor / rho * piNeqNorm) – tauMol);
std::cout << “tauTurb: ” << tauTurb << std::endl << std::flush;
/// Effective realaxation time
V tauEff = tauMol + tauTurb;
return V{1} / tauEff;
} Why can’t I output taueff here, thanks

[Adrian]

You are likely using this collision operator in a CSE-optimized context (e.g. using the SmagorinskyBGKdynamics tuple). This means that the code you modified won’t actually be executed during runtime. You can check without reading the code by adding #define DISABLE_CSE before any OpenLB includes in your case.

[liu]

thank you, I’ve tried to include that code in the channel3d，“#define DISABLE_CSE”. But I found that I still can’t output taueff.

[Adrian]

Unfortunately I can only continue to guess without seeing your code. Did you define the DISABLE_CSE flag before including any OpenLB headers? Are you actually using the Smagorinsky LES model you modified?

Alternatively you can also store tau eff in a dedicated field and output this field as VTK.

[liu]

thank you， I solved the problem using your method.

[Author]

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