Turbulent mixed convection flows computed using low-Reynolds-number and strain parameter eddy viscosity closures

Buoyancy-influenced ascending and descending pipe flows are computed using three eddy viscosity turbulence models: the Launder-Sharma (1974) model is at a 'low-Reynolds-number' scheme, while the Craft et al. (1996) and Cotton-Ismael (1998) closures incorporate dependence on a 'strain parameter'. It is found that the Launder-Sharma model is in closest agreement with direct simulation data for heat transfer, although it is argued that this finding should be interpreted with care. A low Reynolds number extension of the 'buoyancy parameter' of Hall and Jackson (1969) is advanced and shown to improve the collapse of computer heat transfer results at lower levels of buoyancy influence.