Unsteady Loading of Rotor Blades by High Pressure Air Injection

Abstract

A gas turbine engine consists of three primary components: a compressor, a combustion chamber, and a turbine. The operating range, performance, and reliability of gas turbine engines are limited by aerodynamic instabilities that occur in the compressor at low mass flow rates. Two of such compressor instabilities are rotating stall and surge. The stabilization of compression systems by means of active control has been demonstrated on several research compressors using different actuators such as inlet guide vanes, bleed valves, and air injection to manipulate the compressor flow field. This paper presents experimental and model simulated results of the steady and unsteady behaviors of air injection in high speed axial flow compressors that can be used for feasibility studies and control algorithm development. A control oriented model of the unsteady response of the transonic compressor blade rows to steady air injection is presented. This behavior was modeled by one-dimensional flow in a diffusing passage subject to a time varying inlet flow condition in the rotor relative reference frame. The one-dimensional model was then used to provide simplified input boundary conditions for a computational fluid dynamic (CFD) model that predicted aerodynamic loading on a transonic rotor blade due to steady air injection. The aerodynamic loading on a transonic rotor blade due to steady air injection were then simulated from the computational fluid dynamic (CFD) model. The simulation results for an evenly circumferentially spaced discrete number of jet actuators show that the fluctuating loading due to jet injection are non-sinusoidal and periodic. Total pressure, total temperature, and absolute flow angle survey measurements that map out the effect of high pressure air injection on a transonic compressor rotor for different levels of steady injection and different orientations are also presented.