Reynolds averaged computations of turbulent flow in a transonic turbine passage are presented to illustrate a manner in which widely used turbulence models sometimes provide poor heat transfer predictions. It is shown that simple, physically and mathematically based constraints can substantially improve those predictions.
A formulation is developed to apply the two-layer k−ε model to rough surfaces. The approach involves modifying the lν formula and the boundary condition on k. A hydrodynamic roughness length is introduced and related to the geometrical roughness through a calibration procedure. An experiment has been conducted to test the model. It provides data on flow over a ramp with and without surface roughness.
It is shown how natural and forced unsteadiness play a major role in turbine blade trailing edge cooling flows. Reynolds averaged simulations are presented for a surface jet in coflow, resembling the geometry of the pressure side breakout on a turbine blade. Steady computations show very effective cooling; however, when natural—or even moreso, forced—unsteadiness is allowed, the adiabatic effectiveness decreases substantially. Streamwise vortices in the mean flow are found to be the cause of the increased heat transfer.
An eddy-viscosity-based near-wall treatment is proposed to enable large-eddy simulations ͑LES͒ to be performed on coarse grids. This formulation consists of imposing wall stress boundary conditions and an eddy viscosity in the near-wall region. The wall stress and eddy viscosity have a Reynolds-averaged Navier-Stokes-like character and are obtained from an averaged velocity profile of a resolved LES of channel flow at Re = 395. Both are tabulated and are used for the instantaneous quantities. The tabulated eddy viscosity is further corrected using the resolved turbulent stress. Numerical results for flow in a channel at several Reynolds numbers ranging from Re = 395 to Re = 10000 are presented.
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