where ρ is the fluid density, k is the kinetic energy, ε is the
dissipation rate, u is the mean velocity, μeff is the effective
viscosity, αk is the inverse effective Prandlt number for the k
term, αε is the inverse effective Prandlt number for the ε term,
Gk is the generation of turbulent kinetic energy due to mean
velocity gradients, Gb is the generation of turbulent kinetic
energy due to buoyancy, Ym is the contributions of the
fluctuating dilation in compressible turbulence to the overall
dissipation rate, Sk and Sε are the user defined source terms for k
and ε, respectively. Rε is an additional term in the RNG κ-ε
model which is modelled by: