Unsteady Effects on Transonic Turbine Blade-Tip Heat Transfer

Abstract

In a gas turbine engine the blade-tips of the high-pressure turbine are exposed to high levels of convective heat transfer due to the so-called tip-leakage phenomenon. The blade-lift distribution is known to control the flow distribution in the blade tip-gap. However, the interaction between upstream nozzle guide vanes and the rotor blades produces a time-varying flow field that induces varying flow conditions around the blade and within the tip-gap. Extensive measurements of the unsteady blade-tip heat transfer have been made in an engine representative transonic turbine. These include measurements along the mean camber line of the blade-tip which have revealed significant variation in both time-mean and time-varying heat flux. The influences of potential interaction and the vane trailing edge have been observed. Numerical calculations of the turbine stage using a Reynolds averaged Navier-Stokes based computational fluid dynamics code have also been conducted. In combination with the experimental results these have enabled the time-varying flow-field to be probed in the blade-relative frame of reference. This has allowed a deeper analysis of the unsteady heat transfer data, and the quantification of the impact of vane potential field and vane trailing edge interaction on the tip-region flow and heat transfer. In particular, the separate effects of time-varying flow temperature and heat transfer coefficient have been established.