The negatively buoyant turbulent wall jet: performance of alternative options in RANS modelling

The paper describes the application of different levels of turbulence closure and near-wall treatment to the computation of a 2D downward-directed wall jet that encounters a slow, upward-moving flow. The working fluid is water and the two streams may be at the same temperature or the wall-jet fluid may be hotter, leading to significant buoyant effects. The distance of penetration of the wall jet is found to be highly dependent on the turbulence model employed. It is established first that the new analytical wall function (AWF) developed by the authors [Int. J. Heat Fluid Flow 23 (2002) 148] leads to flow predictions in close agreement with a so-called `low-Reynolds-number' treatment where computations extend all the way to the wall. However, for some test cases, both sets of calculations (employing an eddy-viscosity model) indicate too great a penetration of the wall-jet into the opposing stream. The use of the AWF in conjunction with a second-moment closure, particularly one which satisfies the two-component-limit, gives generally closer agreement.