The Influence of Hub Purge Flow Rate on Forced Response in a Low-Pressure Turbine

We present the results of a computational investigation into the influence of hub purge flow mass flow rate on the forcing amplitudes generated on a low-pressure turbine (LPT) rotor cascade by the upstream stator vane passing (SVP). Forcing of this kind is a major driver of high cycle fatigue (HCF) in turbines; however, the influence of hub purge flow, which is mandatory to seal cavities between stationary and rotating rows in turbines and to protect working components from excessively high temperatures, is minimally understood. This study was carried out via time-accurate unsteady aeroelastic simulations of the SPLEEN turbine cascade and is validated against the extensive database of test results obtained for this geometry at the Von Karman Institute for Fluid Dynamics. The effect of purge mass flow rates of 0.5% and 0.9% of the main passage flow are evaluated through measurement of the blade’s unsteady pressure and modal force at the SVP and compared to the nominal `no purge’ case. The introduction of purge flow was shown to reduce the amplitude of the unsteady pressure signal on the blade surface at the hub. However, a change in the phase of the unsteady pressure on certain portions of the blade could still bring about an increase in modal force for certain modes.