Compressor Instability with Integral Methods Episode 1 Part 6 pps

Chapter 3

Parametric Study of Inlet Distortion Propagation

in Compressor with Integral Approach

and Taguchi Method

As mentioned and discussed in previous chapters, the integral method can suc￾cessful to describe the qualitative trend of distorted inlet flow propagation in

the axial compressors. Generally, integral method is applied to the problems of

distorted inlet flow, and the relationships and the effects that some of the key

parameters would have on the propagation of inlet distortion flow were predicted

in qualitative trend, as illustrated in Chap. 1. In this chapter, a Taguchi’s qual￾ity control method [12] will be adopted to justify the integral method and its

research results. The results from Taguchi’s quality control method indicate

that the influence of major parameters on the inlet distortion propagation can

be ranked as, the most one of the ratio of drag-to-lift coefficient, then the inlet

distorted velocity coefficient, and the least one of inlet flow angle. This con￾clusion is different from that in Kim et al.’s research, reason being the later

was carried out using only several cases with integral method. In compari￾son, when Taguchi quality control method is used, the prediction of degrees of

influence by the parameters on the distortion propagation is more reasonable

and accurate.

3.1 Introduction

The gas turbine engine has contributed greatly to the advancement of current

flight capabilities in terms of aircraft performance and range. The propulsive

power of the gas turbine has increased since World War II through higher cycle

pressure ratios and turbine inlet temperature. The compressor is a key compo￾nent to this evolution.

In general, it is more difficult to attain high efficiency on the compressor

stages. Compressors must achieve high efficiency in blade rows in diffusing flow

fields. However, stable operation of the engine depends on the range of stable op￾eration of the compressor and the blade row stall characteristics determine the

limit of stable operation.

Compressor performance is normally characterized by pressure ratio, efficiency,

mass flow and energy addition. Stability is also a performance characteristic. It is

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linked to the response of the compressor to a disturbance that perturbs the compres￾sor operation from a steady point. In transient disturbance, if the system returns to

the original point of operational equilibrium, the performance is regarded as stable.

The performance is considered unstable if the response is to drive operation away

from the original point and steady state operation is not possible [7].

Moreover, there are two areas of compressor performance that relate to stabil￾ity. One deals with operational stability and the other deals with aerodynamic

stability. Operational stability is concerned with the matching of performance

characteristics of the compressor with a downstream flow device such as a throt￾tle, turbine or a jet nozzle.

It is common to see during the operations of the axial-flow compression sys￾tems, as the pressure rise increases, that the mass flow is reduced. A point will be

reached when the pressure rise is a maximum. Further reduction in mass flow will

lead to a sudden and definite change in the flow pattern in the compressor. Beyond

this point, the compressor will enters into either a stall or a surge. Both stall and

surge phenomena are undesirable and they can be detrimental in performance,

structural integrity or system operations ([2], [3], and [7]).

In the area of instability caused by inlet distortion in axial compressor, there is a

considerable interest over the years, with an extensive literature ([1], [3], [4], [5], [6],

[8], [9] and [10]). Among them, Kim et al. [5] successfully calculated the qualitative

trend of distorted performance and distortion attenuation of an axial compressor by

using a simple integral method. Ng et al. [6] developed the integral method and pro￾posed a distortion critical line. By making some simplifications, integral method can

rapidly predict the distorted performance and distortion attenuation of an axial com￾pressor without using comprehensive CFD codes and parallel supercomputer, and

unavoidable, some elegance and detail of flow physics must be sacrificed. Neverthe￾less, the integral method can still provide a useful physical insight about the per￾formance of the axial compressor with an inlet flow distortion.

In current work, using integral method, the behavior of the non-uniform

inlet flow conditions in single and multistage axial compressor is studied. The

distortion flow pattern through the compressor is also investigated. In addi￾tion, the off-line quality control method by Taguchi ([11] and [12]) is used to

analyze the parameters affecting the flow through the compressor.

Kim et al. [5] has concluded that the two most important parameters to control

the distortion propagation are the drag-to-lift ratio of the blade and the inlet flow

angle. Taguchi method is used here to verify Kim et al’s findings on the parameters

influencing the flow through the compressor.

Chapter 3 Parametric Study of Inlet Distortion Propagation in Compressor