Casing-groove optimisation for stall margin in a transonic compressor rotor

The aims of this paper are two-fold. The first goal is to understand aerodynamic blockage related to the near casing flow in a transonic axial compressor using numerical simulations. Secondly, the design of an optimum casing groove for stall margin improvement is attempted using a surrogate-optimisation technique. A blockage parameter (Ψ) is introduced to quantify blockage across the blade domain. A surrogate-optimisation technique is then employed to find the optimum casing groove design that minimises blockage at an axial location where blockage is maximum at near stall conditions. An optimised casing groove that improves the stall margin by about 1% can be found through optimisation of the blockage parameter (Ψ). Optimising for stall margin is rather lengthy and computationally expensive as the stall margin of a compressor will only be known once a complete compressor map is constructed. It is shown here that the cost of the optimisation can be reduced by using a suitably defined blockage parameter as the optimising parameter.