Total Pressure Loss Reduction in Annular Diffusers

抄録

Power output and efficiency of gas turbines depend strongly upon the achievable pressure rise in the subsequent diffuser. In combination with the requirement to keep diffuser length to a minimum, ever steeper opening angles are sought, while avoiding diffuser stall. In terms of diffuser pressure rise, the boundaries of what is achievable can be pushed further if the tip leakage vortices from the last stage are used to re-accelerate the diffuser boundary layer, thus delaying separation onset. Such measures have been shown to decrease total pressure losses as well. In this paper, we show that the benefit of total pressure loss reduction in vortex-stabilised diffusers becomes more pronounced for steeper opening angles by means of a numerically and experimentally validated approach. In extension, we provide evidence that the loss production in highly loaded vortex-stabilised diffusers, which would stall otherwise, can be brought down to the level of non-stalling diffusers. Furthermore, we present a detailed analysis of the different loss mechanisms and their response to vortex- stabilisation of the diffuser.