Advanced methods for multi-row forced response and flutter computations

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Title: Advanced methods for multi-row forced response and flutter computations
Authors: Stapelfeldt, Sina Cornelia
Item Type: Thesis or dissertation
Abstract: This thesis presents the formulation and validation of a novel time-accurate method for the computation of forced response and flutter in multiple blade row turbomachinery. Advanced gas turbine and aeroengine designs require unsteady computational methods to predict aeroelastic behaviour and prevent the occurrence of flutter or forced response which could ultimately lead to engine failure. Currently, time-accurate schemes can successfully represent unsteady flows across multiple blade rows if the domain encompasses the full circumference. However, the large domain size and range of time scales involved make this approach very expensive and unfeasible during the design cycle. More efficient methods take advantage of the inherent time-space periodicity in turbomachines to reduce the computational domain to a single bladed passage per row. These single-passage multi-row methods successfully model unsteadiness due to rotor-stator interaction or blade vibration by applying phase-lagged boundary conditions. However, they are limited to assemblies without passage-to-passage variations in the time-averaged flow field. In multi-stage turbomachinery, where the interaction of rows with unequal blade counts in the same frame of reference creates steady circumferential variations, single-passage methods cannot be applied as no phase-shifted temporal periodicity exists between adjacent passages. Similarly, it is not possible to represent non-axisymmetries such as inlet distortions or stagger profiles using a single passage approach. The time-domain Fourier method presented in this thesis models multi-row non-axisymmetric flows on a reduced number of passages. In order to capture stationary variations, the flow inside several discrete passages, which are located at different circumferential positions, is solved using a time-accurate scheme. Boundary conditions at the azimuthal and inter-row surfaces are approximated from a time-space Fourier series and couple the individual passages. The method is validated for several applications including low engine order forcing in an aerodynamically mistuned assembly and rotor-rotor interaction. It is demonstrated that, within the limit of the Fourier approximation, the resulting solution is equivalent to the full circumference solution and requires only a fraction of the computational resources.
Content Version: Open Access
Issue Date: Oct-2013
Date Awarded: Feb-2014
Supervisor: di Mare, Luca
Sponsor/Funder: Innovate UK
Rolls-Royce Ltd
Funder's Grant Number: MEDY_P28019
Department: Mechanical Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Mechanical Engineering PhD theses

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