The Research Of Aerodynamic Performance Of A Very High Loading LP Turbine Blade

Reduced the weight of LP turbines for aircraft engines, demands small size or few airfoils; which means the lowest possible Reynolds number, the Highest possible loaded and the highest possible efficiency. Recent research has revealed positive effects of unsteady flow on the development of profile boundary layers in LP turbine cascades at conditions with a suction side separation bubble. Compared to steady flow, a reduction of profile loss over a broad range of Reynolds-numbers has been shown.In this paper, the aerodynamic performance and separation bubbles in VKI very high loaded low pressure turbine blade for a wide operating range has been studied. This turbine cascades have been designed to have a strong separation bubble in the trailing edge region of the suction sides, therefore possessing high loss at steady inlet flow conditions and at low Reynolds-numbers compared to a conventional design. Separation bubbles in LP turbine blade boundary layer, under low Reynolds steady flow and periodic wake flow conditions is numerical simulated. A wake generator has been added in order to simulate a moving blade row upstream of a linear turbine cascade. The wakes are generated with cylindrical bars moving in the cascade inlet.By analyzing the results of numerical, combining with the results of previous experimental at the VKI, conclusions are drawn as follows:The position of the suction side velocity peak that changes with the incidence and the Reynolds has a strong influence on the flow behavior and thus on the performance. The cascades show a positive influence of upstream wakes to the boundary layer of the suction side, compared to single cascades, with respect of at design conditions of the LP turbine cascades with upstream wakes passing, the momentum and kinetic energy increased in the boundary layer of the downstream cascades. The boundary layer thickness reduced the separation bubble in the trailing edge region of the suction sides disappeared. Further it was observed that incoming wakes are able to suppress or at least reduce the time-mean extent of a separation on the suction side boundary layer.Consequently, by taking into account the positive effects of wake-induced transition during the design process, new high loading blade with nearly the same low losses at unsteady inlet flow conditions could be achieved. This leads to a reduction of weight and cost of the whole LP turbine module for a constant stage loading.