Unsteady Simulation of the Stall Inception Process in the Compression System of a US Army Helicopter Gas Turbine Engine - Final Year Progress

Abstract

The operational envelope of gas turbine engines such as employed in the Army Blackhawk helicopter is constrained by the stability limit of the compression system. Stall control technologies developed at the ARL Vehicle Technology Directorate and NASA Glenn Research Center to improve the stable operating range of 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. To provide improved understanding, time accurate CFD simulations are being computed at full-scale actual engine conditions using the parallel solver, TURBO, developed at Mississippi State University (MSU) with support from NASA, DoD, and industry. As a compressor nears stall the flow field is no longer periodic from passage to passage, therefore full-annulus (i.e., all blade passages of every blade row) 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. Unsteady full-annulus simulations of both a single stage axial and centrifugal compressor, for which detailed experimental data are available, provide validation of the TURBO code for subsequent use in predicting the stall inception processes in an axicentrifugal multistage compressor employed in the Army Blackhawk helicopter. The simulations show the inception of stall and subsequent evolution into a fully developed stall cell. Also, shown are the predictions of range extension with stall control and comparison to measurements. Finally, a status of the unsteady fullannulus simulations of the compression system components of the U.S. Army Helicopter Gas Turbine Engine is presented. All military and commercial gas turbine engine systems can benefit from the proposed work. In the future, this work could lead to new gas turbine engine designs with resistance to compressor stall and thus improved combat capability. This work 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. This paper presents final-year progress on this challenge project.