Transition and heat transfer predictions in a turbine cascade at various free-stream turbulence intensities through a one-equation turbulence model
The one-equation Spalart-Allmaras turbulence model, coupled with criteria for the prediction of the transition onset, is employed for the numerical prediction of the heat transfer along the nozzle guide vanes of a high-pressure turbine, at various operating conditions. Emphasis is put on how to overcome a known shortcoming of the Spalart-Allmaras model, i.e. its insensitivity to free-stream turbulence. For this purpose, an extra viscosity coefficient is defined and used in the mean flow equations. This extra viscosity is proportional to the free-stream turbulence with a damping in the boundary layer. Its use is adequate to circumvent the aforementioned weakness of the Spalart-Allmaras model, without any other intervention in the model itself. For the prediction of the onset of transition, the Abu-Ghannam and Shaw and the Mayle criteria are used, depending on the level of free-stream turbulence. Both yield very satisfactory predictions in a wide range of Reynolds numbers and/or turbulence intensities. From a numerical point of view, this paper proposes techniques for the implementation of the solution method on unstructured grids with triangular elements and reconfirms findings of previous works, like the suitability of the containment-circle tessellation in highly stretched grids. Copyright (C) 2002 John Wiley Sons, Ltd.
transition heat transfer spalart-allmaras turbulence model unstructured grids free-stream induced viscosity turbine flows