Annular Cascade for Radial Compressor Development

Abstract

A full-annulus cascade for radial compressor stator development has been designed and commissioned. The cascade has been developed for the rapid screening of novel stator concepts to facilitate risk mitigation in the early design phase and the validation/calibration of numerical predictions. The rig consists of two main parts. The first part is comprised of an exchangeable set of stationary preswirl vanes that have been designed to mimic discrete points on the operating characteristic of the impeller. The second part consists of a diffuser, bend and return channel with return channel vanes that can also be quickly exchanged. All exchangeable parts are manufactured by rapid prototyping, allowing rapid turnaround times from aerodynamic design to full validation. This is achieved at a significantly lower cost than that of a full rotating test. This investigation summarizes the experimental results and numerical predictions of two test rigs that were designed to study the effect of diffusion ratio, i.e. the ratio of the maximum outer diameter at the top of the bend to the exit of the impeller, on stator performance. To further investigate the sensitivity of the aerodynamic performance to different flow conditions, metal gauzes were positioned immediately downstream of the trailing edges of the preswirl vanes. This allowed the modification of angle and pressure distributions in the diffuser and bend as well as the setting of different turbulence conditions (intensity and length scale) in the downstream sections.