Wake-Wake Interactions and its Potential for Clocking in a Transonic High Pressure Turbine

Two-dimensional unsteady Navier-Stokes calculations of a transonic single stage high pressure turbine were carried out with emphasis on the flow field behind the rotor. Detailed validation of the numerical procedure with experimental data showed excellent agreement in both time-averaged and time-resolved flow quantities. The numerical time-step as well as the grid resolution allowed the prediction of the Kármán vortex streets of both stator and rotor. Therefore the influence of the vorticity shed from the stator on the vortex street of the rotor is detectable. It was found that certain vortices in the rotor wake are enhanced while others are diminished by passing stator wake segments. A schematic of this process is presented. In the relative frame of reference the rotor is operating in a transonic flow field with shocks at the suction side trailing edge. These shocks interact with both rotor and stator wakes. It was found that a shock-modulation occurs in time and space due to the stator wake passing. In the absolute frame of reference behind the rotor a 50% variation in shock strength is observed according to the circumferential or clocking position. Furthermore a substantial weakening of the rotor suction side trailing edge shock in flow direction is detected in an unsteady flow simulation when compared to a steady state calculation which is caused by convection of upstream stator wake segments. The physics of the mentioned unsteady phenomena as well as their influence on design are discussed.