Using Annulus Contouring to Compensate Compressor Mis-Matching Effects in the Presence of Casing Treatments

摘要

Axial slot casing treatments have shown their ability to enhance the stability of transonic axial compressor rotors at near stall conditions. This passive casing treatment type is pressure driven and stabilizes the near casing flow field by recirculating flow from a downstream part of the rotor passage to a location in front of the rotor leading edge. No active control mechanisms are installed to regulate the re-circulated mass flow rate. Well-designed axial slot casing treatments may also have a positive effect on peak efficiency point at design speed of the treated rotor - despite the deteriorating effect of re-circulation [1]. For reasons of space, casing treatments are mostly suitable for compressor front stages. Since this part of the compressor is highly loaded at part-speed, the application of axial slot casing treatments on the first rotor may be able to stabilize the compressor at part-speed conditions in particular. Most of the previous studies in literature have been carried out on a simplified rotor only model to evaluate the working principle of different casing treatment types and their influence on rotor stability. However, a profound knowledge of the casing treatment's performance within a realistic multi-stage setup is necessary to use casing treatments in real engine applications. For this purpose, CFD studies are carried out on a three-stage transonic axial compressor setup. A realistic hub and casing contouring, as well as realistic geometries of variable stator vanes are considered, including hub and tip clearances and shrouded cavities. An axial slot casing treatment is applied on the first rotor. With this setup, the influence of the axial slot casing treatment on the multi-stage performance at part-speed conditions is evaluated. Special attention is paid to the radial-mismatch effects while operating the compressor within the extended operating range, enabled by using axial slot casing treatments. A second setup with an adapted casing annulus contraction is generated to investigate the possibility of compensating radial mismatch in the presence of axial slot casing treatments. The investigation is divided into two parts: The first part takes a closer look into the stall mechanism of the multi-stage compressor at part-speed conditions. The stabilizing effect of an axial slot casing treatment is investigated and its influence on the stage-matching is evaluated. In the second part, a setup with modified casing annulus contraction is investigated with regard to its influence on radial and stagewise matching in the presence of axial slot casing treatments.