Numerical and Experimental Investigations of Steady Micro-Tip Injection on a Subsonic Axial-Flow Compressor Rotor

Xingen Lu,Zhiting Tong,Wuli Chu,Junqiang Zhu

doi:10.1155/ijrm/2006/71034

Abstract

Steady tip injection has been demonstrated to be an effective means of extending the stable operating range of a tip-critical compressor. This study presents a state-of-the-art design for the tip injection through the casing with flush-mounted inclined holes and the effectiveness of steady micro-air injection to enhance stability in a subsonic axial-flow compressor rotor using an external-air supply. For the tested rotor, experimental results demonstrate that at 53% design speed, the stalling mass flow can be reduced by 7.69% using an injected mass flow equivalent to 0.064% of the annulus flow. Time-dependent CFD simulations were conducted to identify the physical mechanic that accounts for the beneficial effects of the steady micro-air injection on the performance and stability of the compressor. Detailed analyses of the flow visualization at the tip have exposed the different tip flow topologies between the cases without tip injection and with tip injection. It was found that the primary stall margin enhancement afforded by the steady micro-air injection is a result of the tip-clearance flow manipulation. The repositioning of the tip-clearance vortex further towards the trailing edge of the blade passage and delaying the movement of incoming/tip-clearance flow interface to the leading edge plane are the physical mechanisms responsible for extending the compressor stall margin.

Highlights

Adequate stability is an important feature of any compressor design
The effect of the steady micro-tip injection was investigated by applying it to a single-stage axial-flow compressor, but as a starting point was tested on the isolated rotor, with the rear stator removed
It is clear from the figures that steady micro-tip injection can improve stall margin and isentropic efficiency through the mass flow range and

Summary

Introduction

Adequate stability is an important feature of any compressor design. The desire to reduce compressor size, weight, and complexity by reducing the number of stages and eliminating variable vanes leads to higher loading per stage, which tends to reduce the stable operating range of compressors. The safe operating range of a gas turbine compressor is limited by the onset of dynamic instabilities of the fluid at low mass flow rates. The two classes of instabilities, rotating stall and surge, can cause unsteady stresses in the compressor blades and reduce the compressor performance. Sustained operation with rotating stall can lead to excessively high turbine temperatures due to the decreased mass flow through the engine. To provide adequate stall margin, the compressor may operate away from the optimum efficiency point. For these reasons, there has been a fairly constant activity over the last decade devoted to the early detection of compressor instability and to the development of active and passive techniques aimed at broadening the compressor operating range

Methods

Results

Conclusion