Time accurate unsteady simulation of the stall inception process in the compression system of a US Army helicopter gas turbine engine

Abstract

The operational envelope of gas turbine engines employed in the Army Blackhawk helicopter is constrained by the stability limit of the compression system. Technologies developed to improve the stable operating range of gas turbine compressors lack fundamental understanding beneficial to design guidance. Improved understanding of the stall inception process and how stall control technologies mitigate such will provide compressors with increased tolerance to stall, thereby expanding the operational envelope of military gas turbine engines. Compressors which consist of multiple stages of stationary and rotating blade rows can include shocks, vortices, separations, secondary flows, shock/boundary layer interactions, and turbulent wakes, all of which grow in severity as a compressor approaches stall. As a compressor nears stall the flow field is no longer periodic from passage to passage so all blade passages must be computed. For a typical multistage compressor this becomes a formidable computational challenge requiring access to massively parallel machines in order to meet the computational and memory demands of the problem. We are using a time-accurate CFD code to simulate the unsteady stall inception process, both with and without stall control technology, in the compression system of an army gas turbine engine. We will provide the first-ever 3-dimensional viscous time-accurate simulation of the stall inception process in a multistage compressor, providing insight into the causal link between compressor blade design parameters and the stable operating limit, which will be used to guide new design practices leading to compressor designs with increased tolerance to stall. We present progress to date on this challenge project.