Aerodynamic Loading Distribution Effects on Off-Design Performance of Highly Loaded LP Turbine Cascades Under Steady and Unsteady Incoming Flows

Abstract

The present work is part of a continuous cooperation between GE AvioAero and the University of Genova aimed at understanding the detailed flow physics of efficient highly loaded LPT blades for aeroengine applications. In this paper the effects of the aerodynamic loading distribution on the performances of three different cascades with the same Zweifel number have been experimentally investigated under steady and unsteady incoming flow conditions. Measurements have been carried out for several Reynolds numbers (in the range 70000<Re<300000) with an incidence angle variation of ±9°, in order to cover the typical realistic LP aeroengine turbine working range on design and off-design conditions. Profile aerodynamic loadings and total pressure loss coefficients have been evaluated for the different cases. Efficiency data clearly highlight that at nominal incidence an aft loaded cascade provides the lowest profile losses when the boundary layer is attached to the wall, as it occurs in the unsteady case or at high Reynolds numbers. Only at the lowest Reynolds number in the steady case, a front loaded profile is preferable since it helps to prevent a laminar boundary layer separation. Moreover, the aft loaded profile has also shown a better robustness to incidence angle variation, both for the steady and the unsteady inflow conditions. Indeed, the growth of profile losses with incidence is weaker for the aft loaded cascade with respect to the front and the mid loaded ones. However, irrespective of the loading distribution the loss trend vs incidence angle has been found to be completely different between the steady and the unsteady operations. Results in the paper give a clear overview of the impact of the loading distribution on profile losses as a function of Reynolds number, as well as a detailed view of the influence due to the loading characteristics on incidence robustness under the realistic unsteady inflow case.