Effect of buoyancy on turbulence in the entrance region of vertical duct flow

Abstract

This work consists of a numerical investigation on the effect of buoyancy on the thermal developing mean and turbulence fields for buoyancy-aided and buoyancy-opposing channel flows. The geometry considered was vertical pipe flow and an Algebraic Stress Model for turbulence was used in conjunction with a marching-forward finite-difference numerical scheme. Calculations were performed for mercury (Pr=0.025) and for Ra/Re2=1.2×105, where Ra is the Rayleigh number and Re the Reynolds number. An adiabatic entry length of 67 diameters was used before a heated section of another 74 diameters was computed. Results for the thermal developing region are presented for the friction factor ff the Nusselt number Nu, the axial velocity U and for the turbulent kinetic energy k. Predictions are also reported for the axial and radial turbulent fluxes.