Influence of a Shroud Axisymmetric Slot Injection on a High Pressure Turbine Flow

Abstract

This paper focuses on an axisymmetric slot injecting cooling air at the casing between the stator and the rotor in a one-stage unshrouded transonic high pressure turbine. This configuration has been studied with the help of unsteady RANS computations with and without the slot. Special care has been taken to model and describe the interaction induced unsteady mechanisms. It has been found that the cooling air is ejected from the axisymmetric slot at a fixed position with respect to the stator vanes, with a much lower incidence angle than the main stream. The flow through the rotor passage is highly modified and reveals an unsteady behaviour which highlights the necessity of using unsteady simulations in order to accurately model such a configuration. The effect on the efficiency and on the repartition of loss generation has been determined. As several different definitions of the efficiency can be used for cooled turbine cases, this choice is discussed. In particular, Young & Horlock’s “Weighted Pressure” definition, which takes into account some unavoidable mixing losses in the definition of the ideal process, is evaluated. With this definition, the slot does not yield any significant decrease in overall efficiency.

Flow mechanisms in axial turbine rim sealing

“…Similar unsteady flow features to those for rim seals have been identified in a stationary shroud cavity supplying cooling air to the main annulus upstream of the turbine blades through a chute shaped channel by Tang et al [51]. This geometry corresponded to a high pressure turbine stage of a helicopter engine designed by Safran Turbomeca.…”