Axial Compressor Stage Analysis Through a Multi-Block 3-D Navier-Stokes Solution Method

Abstract

A method for the analysis of low-speed flows in compressor stages through a steady, 3-D, multi-block, Navier-Stokes solver is presented. For a complete stage, two pairs of 3-D grid blocks, one for the rotor and one for the stator, are used. The combination of two grids per row aims at the accurate modelling of the flow in the clearances between blade tips of finite thickness and annular walls. Thus, with such a numerical tool, the effect of rotor tip-clearance on the downstream stator performance, can be studied. Within each grid block, governing equations are solved in a segregated manner through the inversion of a single scalar coefficient matrix for all but the continuity equation. For the latter, a pressure correction equation is solved using a generalized residual minimization scheme. The interfaces between rows are treated through a simple mixing approach, based on the communication of circumferentially area-averaged quantities. The interfaces between grid blocks in the same row are treated by means of fake cells. Both interfacing schemes do not badly affect the convergence of the code. The method is used for the analysis of the third stage of a four-stage, low-speed compressor, for which unsteady flow phenomena do not dominate the physics of the flow. Numerical predictions are compared to data from experimental work carried out at the Cranfield University test rig.