Development of a Phase Lag Approach for the Numerical Evaluation of Unsteady Flows

The importance of the knowledge of the unsteady interaction physics in modern gas turbines has grown during the last years following the improvements of the design tools. The numerical simulation of the flow field inside the turbines could provide the required information during the design process, but any steady assumption must be discarded. In fact, the stator/rotor interaction is mainly a 3D unsteady phenomenon driven by the wake/shock/rotor interaction, the secondary flows development and chopping and the hot fluid redistribution on the rotating and stationary parts. A number of numerical methods have been proposed to threat the unsteady interaction on the stage interfaces and the periodic boundary conditions due to the different blade number of the compressor and turbine rows. In this paper, the most important methods for the unsteady stator/rotor interaction are described and commented. Furthermore, a new unsteady method based on the “phase lag” assumption is implemented in the in-house HybFlow code and applied on a 2D linear test case obtained from the CT3 test case, experimentally investigated at the von Karman Institut in the frame of EU funded TATEF2 project. The results obtained in the numerical analysis are reported and commented with respect to the experimental data.