A New Approach to Predicting Annulus Wall Boundary Layers in Axial Compressors

Abstract

This paper introduces a new phenomenological approach to modelling the end-wall effects. It is based on explicit calculations of the annulus wall boundary layers by Hirsch and de Ruyck's method, with significant changes to allow tip clearance effects to be represented, together with explicit calculations of the secondary flows outside the boundary layers using Marsh's equations. To achieve this, the secondary vorticity is computed throughout the compressor. A new simple model for the tip clearance vorticity is added. It is shown, by comparison with Salvage's cascade measurements and Inoue's isolated rotor measurements at varying tip clearance, that the method is capable of satisfactory predictions of the pitchwise-average local deviation and loss near the end-walls. The model is only accurate, however, when there is no significant end-wall flow separation. Two examples of complete multistage low-speed compressors are given. It is concluded that a promising foundation has been presented for a more satisfactory and more accurate way of predicting the end-wall effects than any published purely empirical scheme.