Time Resolved Investigations of an Axial Compressor With Casing Treatment: Part 2 — Simulation

Abstract

A casing treatment with axial and radial skewed slots ending in a plenum chamber has numerically been investigated at a highly subsonic axial compressor stage. The aim was to understand the physical phenomena of this treatment family that are responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. Unsteady 3D Reynolds-averaged simulations were performed with the commercial CFD Code TASCflow 2.12. The closure problem was faced with a standard k-ε high Reynolds turbulence model and a logarithmic wall function. Two configurations with solid casing and casing treatment were investigated at the operating points with maximum efficiency and on the stability line. The experimentally gained performance results of this configuration show an extension of the operating range of approximately 50% based on the operating range at nominal speed, while the efficiency for design conditions falls by 1.4%. Apart from this, measurements at part load conditions show operating points without any loss in efficiency. The numerical simulations predict this efficiency drop as well. The detailed analysis is performed for the solid casing and casing treatment configuration at the operating point on the stability line. Influences of the incidence flow, the tip clearance vortex and the blade suction side separation were investigated. Special interest is directed towards the interaction of the casing treatment with the blade passage flow field and a detailed analysis of the flow inside the casing treatment, the effect of the plenum chamber and the interaction with the treatment slot flow is performed.