The Influence of Diffuser Vanes on Stall and Surge in an Industrial Centrifugal Compressor

The influence of diffuser vanes on the stability behavior of an industrial centrifugal compressor (impeller outlet diameter d2 = 330 mm, machine Mach number Mu2 = 1.1 and pressure ratio πvaneless = 2.35) with IGV and volute is experimentally investigated with two different diffuser configurations: vaneless and vaned. Inlet tip recirculation was analyzed and found to be suppressed by the diffuser vanes on almost all performance curves. The instability phenomena are captured by 29 transient pressure transducers in the impeller and diffuser shroud. These measurements show that mild surge is suppressed by the diffuser vanes at low rotational speeds. The pressure transducers are also used to accurately identify rotating stall. The properties of rotating stall are analyzed in terms of number and rotational speed of the stall cells as well as their streamwise propagation through the compressor stage. The rotating stall properties are significantly influenced by the diffuser vanes. The cells co- and counter-rotate at slower rotational speed with the vaned diffuser. Counter-rotating cells emerge from the diffuser outlet and propagate upstream through the compressor. In contrast, co-rotating stall cells form at the impeller leading edge and propagate downstream through the compressor. In one operating point, there are even co- and counter rotating stall cells present that superpose. These results can be used to prevent potentially damaging operating conditions of future centrifugal compressor stages.