Aeroengine High-Attitude/Low Mach Number Oscillations: Mechanism and Prevention Design

Jiqiang Wang,Antonio Viviani

doi:10.1155/2021/8881951

Abstract

The issue of aeroengine oscillations over high-attitude and low-speed flight envelope has been an unsolved problem due to their classified nature and hard reproduction in simulated altitude test stand. Efforts have been sought for either structural integrity or component damage. However, it is rarely realized that the oscillations can be an inherent property of the engine itself. Consequently, a dynamical system approach is proposed in this paper to demonstrate that engine oscillations are recurring over high-attitude and low-speed flight envelope, yet they can be suppressed through appropriate control designs. However, the resulting design can be compromised with the conventional high-gain control where the transient and steady-state performance must be balanced with disturbance attenuation performance. Examples are given to illustrate and validate the claims made through the en route analysis.

Highlights

Aeroengine oscillations can cause detrimental effects on engine components, and they can propagate through the pylon to aircraft suffering from structural vibration and passenger discomfort [1, 2]
The design procedure usually works as follows: the flight envelope is divided into several regions, and within each region, a linear model is obtained for the operational condition, e.g., small perturbation state space model or finite impulse response model; the controller is designed for each linear model using, e.g., PID control, LQR/LTR, or H∞ optimal control [13,14,15]; the full flight envelope control is achieved through gain scheduling
What has been proposed in this paper is that disturbance response is an inherent property of any dynamical system; oscillations are unavoidable for systems under disturbance excitations

Summary

Introduction

Aeroengine oscillations can cause detrimental effects on engine components, and they can propagate through the pylon to aircraft suffering from structural vibration and passenger discomfort [1, 2]. The design procedure usually works as follows: the flight envelope is divided into several regions, and within each region, a linear model is obtained for the operational condition, e.g., small perturbation state space model or finite impulse response model; the controller is designed for each linear model using, e.g., PID control, LQR/LTR, or H∞ optimal control [13,14,15]; the full flight envelope control is achieved through gain scheduling (usually, scheduling variables are T1 and P1, and the PI controller parameters are corrected based on the scheduling variables) This has been the standard practice in modern engine control designs and has resulted in fairly acceptable performance. The corresponding nonlinear design approaches are deployed for aeroengine control, see [21, 22] and references therein Even after these inexhaustible efforts to prevent aeroengine oscillations, one situation is still recurring in practice where the engine oscillates violently over high-attitude and low Mach number flight envelope.

Problem Formulation and Preliminaries

Dynamical System Approach to Engine Oscillations

Prevention Design of Engine Oscillations

Findings

Discussions and Conclusions