Optimizing surge margin and efficiency of a transonic compressor

It has been shown in several cases that casing treatments can improve the surge margin of a compressor. The question that is often left unanswered when designing and optimizing a casing treatment for a given compressor stage is whether the casing treatment can still improve the performance and surge margin when used on an aerodynamically improved rotor. The current work includes the influence of the rotor geometry and casing geometry in the analysis. Several optimizations with equal objectives, to improve surge margin and efficiency, were performed. First the different components were optimized separately. The possible impact of optimizing the rotor, the casing geometry and the casing treatment on surge margin and efficiency are compared in terms of global performance and aerodynamic effects. It is then analyzed how combinations of optimized geometries perform. Of particular interest is how the circumferential grooves perform when used in combination with the optimized blade geometry. The optimizations were performed using state of the art CFD and optimization procedures. Constraints on boundary conditions, mass flow rates and stresses were applied in order not to change the behavior of the compressor at design point significantly or to deteriorate the structural mechanics.