CALCULATION OF TRANSITIONAL BOUNDARY-LAYERS WITH AN IMPROVED LOW-REYNOLDS-NUMBER VERSION OF THE K-EPSILON TURBULENCE MODEL

Several well-known low-Reynolds-number versions of the kappa-epsilon m odels are analyzed critically for laminar to turbulent transitional fl ows as well as near-wall turbulent flows from a theoretical and numeri cal standpoint. After examining apparent problems associated with the modeling of low-Reynolds-number wall damping functions used in these m odels, an improved version of the kappa-epsilon model is proposed by d efining the wall damping factors as a function of some quantity (turbu lence Reynolds number Re-t), that is only a rather general indicator o f the degree of turbulent activity at any location in the flow rather than a specific function of the location itself, and by considering th e wall limiting behavior, the free-stream asymptotic behavior, and the balance between production and destruction of turbulence. This new mo del is applied to the prediction of ( I) transitional boundary layers influenced by the freestream turbulence, pressure gradient, and heat t ransfer; (2) external heat transfer distribution on the gas turbine ro tor and stator blade under different inlet Reynolds number and free-st ream turbulence conditions. It is demonstrated that the present model yields improved predictions.