On the Simulation of unsteady Turbulence and Transition Effects in a Multistage Low Pressure Turbine, Part II: Full-Wheel Simulation

Kurzfassung

This is the second part of a series of three papers on the simulation of turbulence and transition effects in a multistage low pressure turbine. In this second part, the investigated two-stage low pressure turbine is described and results of a nonlinear full-wheel time-domain simulation are presented, analyzed and compared with the available experimental data. Furthermore, recent improvements to the CFD solver TRACE are described in brief that lead to significantly reduced wall-clock times for such large scale simulations. The utilized models match those used in the Harmonic Balance (HB) based simulations that are presented in the third paper of this series, such that the full-wheel result can be utilized to validate the HB result. Transition, flow separation and wall pressure fluctuations on the stator blades of the second stage are analyzed in detail. A strong azimuthal Pi-periodicity is observed, manifesting in a significantly varying stability of the midspan trailing edge flow with a quasi-steady closed separation bubble on certain blades and highly dynamic partially open separation bubbles with recurring transition and turbulent reattachment on other blades. The energy spectrum of fluctuating wall quantities in that regime shows a high bandwidth and considerable disharmonic content, which is challenging for the HB based simulations.