Three-dimensional through-flow modelling of axial compressor rotating stall and surge.

Abstract

The operation of an aero-engine is limited by the occurrence of compressor stall, and compressor performance is sacrificed to maintain a sufficient margin of operation. Compressor stall also plays an important part in the event of a shaft failure, and in determining if this will result in a rotor burst. In Cranfield University a tool to model the whole engine during shaft failure has been developed, but it requires the knowledge of the compressor performance during stall. Low order 1D, 2D or 3D methods to model compressor stall exist in literature, but they are still at a low maturity level and not applicable for commercial use. The only methods available are expensive experimental testing and transient 3D CFD, which has unacceptable computational costs. The objective of this PhD project has therefore been identified in the development of a fast and robust 3D tool to model compressor stall, and in its validation with data from low-speed experimental rigs. The tool created is a three-dimensional through-flow code which uses empirical correlations to model the blade row performance. A novel methodology has been developed to estimate the performance of blade rows in reverse flow, based on previous models of separated blade passages. The Godunov scheme has been chosen to create the 3D, unsteady, cylindrical, compressible, finite volume method Euler solver on which the code is based. Appropriate body forces and boundary conditions have been chosen and implemented. The validation carried out on two low-speed compressors demonstrates the applicability of the proposed formulation, with successful prediction of the performance during reverse flow, rotating stall and surge. The speed, size and structure of the rotating stall cell have been successfully matched to experimental data. The developed tool can reproduce the forward flow, reverse and rotating stall regions of the map in less than 72 hours, at a computational speed unrivalled by modern commercial CFD codes.