2005 Ohio Student Research Forum

Abstract

Aeromechanical Feedback Control of High-Speed Axial Compressor Stall
Keith Coleman
Ohio State University, Department of Civil Engineering
Mentor: Dr. Oliver McGee

The operating range of aeroengine compression systems is limited by two classes of aerodynamic instabilities known as rotating stall and surge. Rotating stall is a multi-dimensional instability in which regions of low or reversed mass flow (i.e., stall cells) propagate around the compressor annulus, due to variations of the angle of attack of the air fluid on the airfoil (i.e., rotor or stator). Surge is a primarily one-dimensional instability of the entire pumping system (compressor, ducts, combustion chamber, and turbine). It includes periods of flow reversal through the entire machine. In high speed compressor hydrodynamics, rotating stall is generally encountered first, which then “triggers” surge. Therefore the focus of this work will be on rotating stall. With either instability, the compression system will experience a significant loss in performance, which sometimes includes mechanical failure.

An experienced based approach for avoiding such performance loss is to operate the compressor at a safe range away from the point of instability onset (i.e., with stall margin). The stall margin ensures that the engine can withstand momentary off-design operation. However, this margin reduces the efficiency of the machine.

Proof-of-concept studies have demonstrated the feasibility of aeromechanical control of low-speed stalled compressors. However, some additional questions remain for high-speed devices.1) What are other control stabilization schemes for high speeds in comparison to those found at low speeds? 2) Are there high-speed fluid-structural interactions which should be avoided through tailored structural design? 3) How do the aeromechanical feedback dynamics combine with the pre-stall compressible fluid dynamics to postpone or induce the inception of high-speed rotating stall.

General methods will be developed in this work for the evaluation of passive high-speed compressor stabilization strategies using tailored structural design and aeromechanical feedback control. These passive stabilization strategies will be compared in their performance of several aeromechanical stabilization approaches which could be implemented in high speed axial compressors used by industry.