On the unsteady secondary flow inside a low pressure turbine stage

This thesis addresses the unsteady formation of secondary flow structures inside a turbine rotor passage. Recommendations with respect to state-of-the-art design methods as well as analysis methodologies of turbines are derived from the analysis of this complex time-dependent flow field. The two-stage turbine demonstrator has been tested in the Altitude Test Facility of the Institute of Aircraft Propulsion Systems at the University of Stuttgart. Unsteady multi-stage Reynolds-averaged Navier-Stokes predictions provide the time-resolved data sets. The unsteady flow field inside the rotor passage has been compared to secondary flow studies known from literature. The analysis of the data reveals a non-classical secondary flow field inside the rotor passage. The secondary flow field is dominated by flow structures related to the upstream nozzle guide vane. Today, turbines are frequently optimized using steady CFD to reduce secondary loss. A fundamental requirement for successful numerical optimization is the accurate prediction of the three-dimensional flow field. This thesis shows the improvement of flow field predictions of a turbine stage which may be achieved through the substitution of steady predictions with unsteady predictions.