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 on a three-stage low-pressure turbine. The investigation emphasizes the study of unsteady flow interaction. A time-accurate, Reynolds-averaged Navier-Stokes solver is applied for the computations. Turbulence is modelled using the Spalart-Allmaras one-equation turbulence model. The influence of modern transition models on the unsteady flow predictions is investigated. 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-three-dimensional calculations are conducted on a stream surface around mid-span, allowing a varying stream tube thickness. A three-stage, low-pressure turbine rig of a modern commercial jet engine is used for a study of the unsteady flow interaction. The numerical method is able to capture important unsteady effects found in the experiments, i.e. unsteady transition as well as the bladerow interaction. In particular, the flowfield with respect to time-averaged and unsteady quantities such as surface pressure, vorticity and turbulence intensity is compared with the experiments conducted in the cold airflow test rig.