TurbulentDiffusivity.h

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#ifndef LBM_TURBULENTDIFFUSION_H
#define LBM_TURBULENTDIFFUSION_H
#include <basics/DataTypes.h>
#include <basics/constants/NumericConstants.h>
 
#include <algorithm>
#include <cmath>
 
namespace vf::lbm::advection_diffusion
{
 
enum class TurbulenceModel {
    None,
    Default,
    Moeng,
    AMDStratified
};
 
constexpr real calcTurbulentDiffusivityDefault(real turbulentViscosity, real turbulentPrandtlNumber)
{
    return turbulentViscosity / turbulentPrandtlNumber;
}
 
constexpr real calcTurbulentDiffusivityMoeng(real temperatureGradient, real turbulentViscosity, real buoyancyParameter)
{
    using namespace vf::basics::constant;
    real lengthScale = c1o1;
    const real bruntVaisalaFrequencySquared = buoyancyParameter * temperatureGradient;
    const real subgridTurbulentKineticEnergy = turbulentViscosity * turbulentViscosity;
    const real limit = c76o100 * c76o100 * subgridTurbulentKineticEnergy;
    if (bruntVaisalaFrequencySquared > limit) { // for numerical stability & clips to minimum of 1
        lengthScale = sqrtf((float)limit / (float)bruntVaisalaFrequencySquared);
    }
    const real invTurbulentPrandtlNumber = c1o1 + c2o1 * lengthScale;
    return turbulentViscosity * invTurbulentPrandtlNumber;
}
 
constexpr real calcTurbulentDiffusivityAMD(real SGSConstant, real dvxdx, real dvxdy, real dvxdz, real dvydx, real dvydy,
                                           real dvydz, real dvzdx, real dvzdy, real dvzdz, real dthetadx, real dthetady,
                                           real dthetadz)
{
    using namespace vf::basics::constant;
    const real numerator = -((dvxdx * dthetadx + dvxdy * dthetady + dvxdz * dthetadz) * dthetadx +
                             (dvydx * dthetadx + dvydy * dthetady + dvydz * dthetadz) * dthetady +
                             (dvzdx * dthetadx + dvzdy * dthetady + dvzdz * dthetadz) * dthetadz);
    const real denominator = dthetadx * dthetadx + dthetady * dthetady + dthetadz * dthetadz;
    if (denominator < cSmallSingle)
        return c0o1;
    constexpr real zero = c0o1;
    constexpr real upperLimit = c1o100;
    return std::clamp(SGSConstant * numerator / denominator, zero, upperLimit);
}
} // namespace vf::lbm::advection_diffusion
#endif