Numerical analisys of Weakly turbulent mixed convection flows in a horizontal pipe

Weakly turbulent developing flows in a heated horizontal pipe are investigated numerically, focusing on the effects of mixedconvection, and for two different thermal boundary conditions (BCs), the uniform heat flux condition and the uniform walltemperature condition. The Reynolds number, based on the pipe diameter and bulk velocity, is set equal to Re = 5750 and the molecular Prandtl number Pr = 12. For the sake of comparison, the Grashof number values GrH = 3×108 and GrT = 2.3×1010 are chosen for isoflux and isothermal boundary conditions, respectively. Turbulence is modeled by using alternative RANS approaches. Four RANS models are considered, namely the realizable k-e (RKE), the renormalization-group k-e (k-e RNG), the Gibson’s q-z model, and the Shear-Stress Transport k-w model (k-w SST). Results allow to discriminate the performance ofthe different turbulent models and give hint on the effects of the buoyancy induced flow over the leading forced component.The effect of the thermal boundary condition is finally discussed.