Numerical and Experimental Investigation of Unsteady Flow Interaction in a Low Pressure Multistage Turbine

Abstract

The paper presents results of unsteady viscous flow calculations and corresponding cold flow experiments of a three stage low pressure turbine. The investigation emphasize the study of unsteady flow interaction. A time accurate Reynolds averaged Navier-Stokes solver is applied for the computations. Turbulence is modeled using the Spalart-Allmaras one equation turbulence model and the influence of modern transition models on the unsteady flow predictions is investigated. The integration of the governing equations in time is performed with a four stage Runge-Kutta scheme, which is accelerated by a two grid method in the viscous boundary layer around the blades. At the inlet and outlet non-reflecting boundary conditions are used. The quasi 3D calculations are conducted on a stream surface around midspan allowing a varying stream tube thickness. In order to study the unsteady flow interaction a three stage low pressure turbine rig of a modern commercial jet engine is built up. Besides the design point, the Reynolds number, the wheel speed and the pressure ratio are varied in the tests. The numerical method is able to capture important unsteady effects found in the experiments, i.e. unsteady transition as well as the blade row interaction. In particular, the flow field with respect to time averaged and unsteady quantities such as surface pressure, entropy and skin friction is compared with the experiments conducted in the cold air flow test rig.