Unsteady Aerodynamics and Gust Response in Compressors and Turbines

Abstract

A comprehensive series of experiments and analyses was performed on compressor and turbine blading to evaluate the ability of current, practical, engineering/analysis models to predict unsteady aerodynamic loading of modern gas turbine blading. This is part of an ongoing effort to improve methods for preventing blading failure. The experiments were conducted in low-speed research facilities capable of simulating the relevant aerodynamic features of turbomachinery. Unsteady loading on compressor and turbine blading was generated by upstream wakes and, additionally for compressors, by a rotating inlet distortion. Fast-response hot-wire anemometry and pressure transducers embedded in the airfoil surfaces were used to determine the aerodynamic gusts and resulting unsteady pressure responses acting on the airfoils. This is the first time that gust response measurements for turbines have been reported in the literature. Several different analyses were used to predict the unsteady component of the blade loading: (1) a classical flat-plate analysis, (2) a two-dimensional linearized flow analysis with a ‘frozen gust’ model, (3) a two-dimensional linearized flow analysis with a “distorted gust” model, (4) a two-dimensional linearized Euler analysis, and (5) a two-dimensional nonlinear Euler analysis. Also for the first time, a detailed comparison of these analyses methods is made and the importance of properly accounting for both vortical and potential disturbances is demonstrated. The predictions are compared with experiment and their abilities assessed to help guide designers in using these prediction schemes.

Transonic Rotor/Stator Interaction Using a 3-D Linearised Unsteady Viscous Flow Model

“…(The potential component was filtered out using the splitting theorem.) The first Fourier component, usually referred to as "gust" (Manwaring and Wisler, 1993), clearly shows the three-dimensionality of the NGV wake towards the root section. A very large velocity deficit occurs half a cycle or so earlier than that for the midheight wake.…”

“…Such interactions are purely inviscid, hence the term potential interaction. Although it is possible to consider one bladerow only, either the stator or the rotor, with the unsteady pressure being specified as a boundary condition (Korakianitis, 1993;Manwaring and Wisler, 1993), it is probably better to perform a stage calculation (Giles, 1990b;Sayma et al, 1999), especially when the spacing between the bladerows is small, and when there are shock waves moving in the region between them.…”

An Integrated Nonlinear Approach for Turbomachinery Forced Response Prediction. Part I: Formulation

“…A full stator}rotor interaction model using Navier}Stokes equations was developed in 2-D by Giles (1990b), and in 3-D by Rai (1987b). Results from some of the models above are compared with experimental data in the paper by Manwaring & Wisler (1992). A study of varying the blade numbers is reported by Korakianitis (1988 (1992), which presents an industrial forced response prediction system, also reviews much of the research in this area.…”

Turbine Rotor Generated Forcing Functions for Flow Induced Vibrations

“…Namely, the flow in the rotor frame is spatially periodic, repeating itself every rotor spacing. The axial wave number can then be determined from Equation 6. Thus the axial and tangential wave numbers for the nth harmonic are " S™ η -1.…”