Detailed Experimental and Numerical Investigation of a Transonic Impeller With a Vaned Diffuser

Abstract A modern high efficiency high-speed centrifugal compressor (MU2 > 1.5) was developed with a vaned diffuser for rotorcraft applications, as reported in GT2024-129310. The configuration is comprised of an axial intake, an impeller and a vaned diffuser that are suited for high efficiency applications. Rig test data is based on performance rakes, wall static pressure taps distributed along static parts, dynamic pressure measurements at critical locations, etc. acquired at various rotational speeds. Impeller and diffuser performance are experimentally deduced and flow variables at the exducer are obtained from measured quantities using mass flow rate equation with two velocity components. Relevant blockage correlation from Ref. [8] is utilised and slip factor based on entire data set is calculated as 0.96±0.03. A modern slip factor correlation including the effect of blade loading towards the trailing edge, from Ref. [9] is compared against the deduced value and match is found very satisfactory. Three-hole probe data confirms the impeller pressure ratio and the corresponding flow angle. Diffuser performance is obtained between the stations of the vaneless space up to exit rakes. Diffuser throat is found to be slightly smaller compared to the desired value for collective choking. Impeller stall is observed up to 95% Nc and diffuser stall occurs from there onwards, in terms of choking, vaned diffuser is responsible for the entire range of operation. Numerical method is validated against test data and different turbulence models are tried. Correction coefficients for numerically generated compressor maps are obtained in terms of mass flow rate, pressure ratio and efficiency.