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

Abstract

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.

Impact of clocking on the aero-thermodynamics of a second stator tested in a one and a half stage HP turbine

“…In other words, the intensity and the locations of static pressure gradients at the exit of the rotor changes according to the location of the rotor in the first stator pitch. This was also observed in numerical simulations (see for example Hummel [2]; Marconcini and Pacciani [18]). These pressure gradients are expected to play a dominant role in the rotor-second stator interaction.…”

“…The surface heat flux is determined thanks to the temperature evolution during the test. Knowing the thermal properties of the ceramic substrate (Ma cor, 2 0.5 ρCk = 2073J m Ks , from Dénos [26]) and applying the mono-dimensional unsteady conduction equation (1), it is possible to determine the temperature profile in the insulating layer at each time step.…”

“…The pitch-wise variation of the total pressure downstream of the stage is usually attributed to what remains from the upstream wake. Tiedemann and Kost [1], Hummel [2] and Miller et al [3] performed unsteady measurements and computations in a single turbine stage configuration; they detailed the mechanisms of interactions between the stator/rotor wakes and the rotor shocks, providing guidelines for the positioning of the next row. In the case of a supersonic vane, Dénos and Paniagua [4] demonstrated that not only the wake but also the stator exit potential field distorted by shocks are responsible of the pitchwise variations at the stage exit.…”

Clocking In Turbines: Remarks On Physical Nature And Geometric Requirements

“…Further behaviour of the stator and rotor wakes can be observed in Fig. 4 being a compilation of the results presented in [23][24][25][26][27]. All wakes leave the rotor moving, generally, in the direction of the main flow velocity w 2 .…”

“…Some initial attempts to take into account vortex dynamics when analysing the stator wake motion through the rotor cascade have been published. A most detailed study was done by Kost et al [23], Tiedemann and Kost [24] and Hummel [25], who examined experimentally and numerically unsteady flow fields generated by stator wakes in rotor passages of a full size aero-engine high-pressure turbine stage having 43 stator blades and 64 rotor blades. Visual studies of the flow inside the rotor passages performed by Kost et al with the aid of coolant injected to the flow at the vicinity of stator blade trailing edges have revealed that on its way through the rotor passage the stator wake forms two separate areas of different-sign vorticity which move one after the other through the passage, thus creating the earlier mentioned negative jet between the blade walls, clearly observed on the numerically calculated distributions of velocity vectors.…”