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Zhao, Fanzhou. "Embedded blade row flutter." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/51151.
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Modern gas turbine design continues to drive towards improved performance, reduced weight and reduced cost. This trend of aero-engine design results in thinned blade aerofoils which are more prone to aeroelastic problems such as flutter. Whilst extensive work has been conducted to study the flutter of isolated turbomachinery blades, the number of research concerning the unsteady interactions between the blade vibration, the resulting acoustic reflections and flutter is very limited. In this thesis, the flutter of such embedded blade rows is studied to gain understanding as for why and how such interactions can result in flutter. It is shown that this type of flutter instability can occur for single stage fan blades and multi-stage core compressors. Unsteady CFD computations are carried out to study the influence of acoustic reflections from the intake on flutter of a fan blade. It is shown that the accurate prediction of flutter boundary for a fan blade requires modelling of the intake. Different intakes can produce different flutter boundaries for the same fan blade and the resulting flutter boundary is a function of the intake geometry in front of it. The above finding, which has also been demonstrated experimentally, is a result of acoustic reflections from the intake. Through in-depth post-processing of the results obtained from wave-splitting of the unsteady CFD solutions, the relationship between the phase and amplitude of the reflected acoustic waves and flutter stability of the blade is established. By using an analytical approach to calculate the propagation and reflection of acoustic waves in the intake, a novel low- fidelity model capable of evaluating the susceptibility of a fan blade to flutter is proposed. The proposed model works in a similar fashion to the Campbell diagram, which allows one to identify the region (in compressor map) where flutter is likely to occur at early design stages of an engine. In the second part of this thesis, the influence of acoustic reflections from adjacent blade rows on flutter stability of an embedded rotor in a multi-stage compressor is studied using unsteady CFD computations. It is shown that reflections of acoustic waves, generated by the rotor blade vibration, from the adjacent blade rows have a significant impact on the flutter stability of the embedded rotor, and the computations using the isolated rotor can lead to significant over-optimistic predictions of the flutter boundary. Based on the understanding gained, an alternative strategy, aiming to reduce the computational cost, for the flutter analysis of such embedded blades is proposed. The method works by modelling the propagation and reflection of acoustic waves at the adjacent blade rows using an analytical method, whereby flutter computations of the embedded rotor can be performed in an isolated fashion by imposing the calculated reflected waves as unsteady plane sources. Computations using the proposed model can lead to two orders of magnitude reduction in computational cost compared with time domain full annulus multi-row computations. The computed results using the developed low-fidelity model show good correlation with the results obtained using full annulus multi-row models.
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Dong, Bonian. "Numerical simulation of wakes, blade-vortex interaction, flutter, and flutter suppression by feedback control." Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134810/.
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Bell, David Lloyd. "Three dimensional unsteady flow for an oscillating turbine blade." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4794/.
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An experimental and computational study, motivated by the need to improve current understanding of blade flutter in turbomachinery and provide 3D test data for the validation of advanced computational methods for the prediction of this aeroelastic phenomenon, is presented. A new, low speed flutter test facility has been developed to facilitate a detailed investigation into the unsteady aerodynamic response of a turbine blade oscillating in a three dimensional bending mode. The facility employs an unusual configuration in which a single turbine blade is mounted in a profiled duct and harmonically driven. At some cost in terms of modelling a realistic turbomachinery configuration, this offers an important benefit of clearly defined boundary conditions, which has proved troublesome in previous work performed in oscillating cascade experiments. Detailed measurement of the unsteady blade surface pressure response is enabled through the use of externally mounted pressure transducers, and an examination of the techniques adopted and experimental error indicate a good level of accuracy and repeatability to be attained in the measurement of unsteady pressure. A detailed set of steady flow and unsteady pressure measurements, obtained from five spanwise sections of tappings between 10% and 90% span, are presented for a range of reduced frequency. The steady flow measurements demonstrate a predominant two-dimensional steady flow, whilst the blade surface unsteady pressure measurements reveal a consistent three dimensional behaviour of the unsteady aerodynamics. This is most especially evident in the measured amplitude of blade surface unsteady pressure which is largely insensitive to the local bending amplitude. An experimental assessment of linearity also indicates a linear behaviour of the unsteady aerodynamic response of the oscillating turbine blade. These measurements provide the first three dimensional test data of their kind, which may be exploited towards the validation of advanced flutter prediction methods. A three dimensional time-marching Euler method for the prediction of unsteady flows around oscillating turbomachinery blades is described along with the modifications required for simulation of the experimental test configuration. Computationalsolutions obtained from this method, which are the first to be supported by 3D test data, are observed to exhibit a consistently high level of agreement with the experimental test data. This clearly demonstrates the ability of the computational method to predict the relevant unsteady aerodynamic phenomenon and indicates the unsteady aerodynamic response to be largely governed by inviscid flow mechanisms. Additional solutions, obtained from a quasi-3D version of the computational method, highlight the strong three dimensional behaviour of the unsteady aerodynamics and demonstrate the apparent inadequacies of the conventional quasi-3D strip methodology. A further experimental investigation was performed in order to make a preliminary assessment of the previously unknown influence of tip leakage flow on the unsteady aerodynamic response of oscillating turbomachinery blades. This was achievedthrough the acquisition of a comprehensive set of steady flow and unsteady pressure measurements at three different settings of tip clearance. The steady flow measurements indicate a characteristic behaviour of the tip leakage flow throughout the range of tip clearance examined, thereby demonstrating that despite the unusual configuration, the test facility provides a suitable vehicle for the investigation undertaken. The unsteady pressure data show the blade surface unsteady pressure response between 10% and 90% span to be largely unaffected by the variation in tip clearance. Although close examination of the unsteady pressure measurements reveal subtle trends in the first harmonic pressure response at 90% span, which are observed to coincide with localised regions where the tip leakage flow has a discernible impact on the steady flow blade loading characteristic. Finally, some recommendations for further work are proposed
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Rauchenstein, Werner J. "A 3D Theodorsen-based rotor blade flutter model using normal modes." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FRauchenstein.pdf.
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Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 2002.Thesis advisor(s): E. Roberts Wood, Mark A. Couch. Includes bibliographical references (p. 55-56). Also available online.
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Höhn, Wolfgang. "Numerical investigation of blade flutter at or near stall in axial turbomachines." Doctoral thesis, KTH, Energy Technology, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2934.
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During the design of the compressor and turbine stages oftoday's aeroengines aerodynamically induced vibrations becomeincreasingly important since higher blade load and betterefficiency are desired. Aerodynamically induced vibrations inturbomachines can be classified into two general categories,i.e. selfexcited vibrations, usually denoted as flutter, andforced response. In the first case the aerodynamic forcesacting on the structure are dependent on the motion of thestructure. In the latter case the aerodynamic forces can beconsidered to be independent of the structural motion. In thisthesis the development of a method based on the unsteady,compressible Navier-Stokes equations in two dimensions isdescribed in order to study the physics of flutter for unsteadyviscous flow around cascaded vibrating blades at stall.
The governing equations are solved by a finite differencetechnique in boundary fitted coordinates. The numerical schemeuses the Advection Upstream Splitting Method to discretize theconvective terms and central differences discretizing thediffusive terms of the fully non-linear Navier-Stokes equationson a moving H-type mesh. The unsteady governing equations areexplicitly and implicitly marched in time in a time-accurateway using a four stage Runge-Kutta scheme on a parallelcomputer or an implicit scheme of the Beam-Warming type on asingle processor. Turbulence is modelled using theBaldwin-Lomax turbulence model. The blade flutter phenomenon issimulated by imposing a harmonic motion on the blade, whichconsists of harmonic body translation in two directions and arotation, allowing an interblade phase angle betweenneighbouring blades. An aerodynamic instability is given whichcan lead to a flutter problem, if the computed unsteadypressure forces amplify the imposed blade motion.Non-reflecting boundary conditions are used for the unsteadyanalysis at inlet and outlet of the computational domain. Thecomputations are performed on multiple blade passages in orderto account for nonlinear effects. Unsteady boundary conditionsare developed considering primary and secondary gust effectstowards the investigation of the forced response problem withthe presented method.
Subsonic massively stalled and transonic separated unsteadyflow cases in compressor and turbine cascades are studied. Theresults, compared with experiments and the predictions of otherresearchers, show good agreement for inviscid and viscous flowcases for the investigated flow situations with respect to thesteady and unsteady pressure distribution on the blade in thevicinity of shocks and in separated flow areas.
The results show the applicability of the new scheme forstalled flow around cascaded blades. As expected the viscousand inviscid methods show different results in areas whereviscous effects are important, i.e. separated flow and shockwaves. In particular, different predictions for inviscid andviscous flow for the aerodynamic damping for the investigatedflow cases are found.
Keywords: turbomachinery, flutter, forced response, gust,unsteady aerodynamics, Navier-Stokes equations, AdvectionUpstream Splitting Method, implicit scheme, non-reflectingboundary conditions, gust boundary conditions, parallelcomputing
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Moyroud, François. "Fluid-structure integrated computational methods for turbomachinery blade flutter and forced response predictions /." Stockholm : Tekniska högsk, 1998. http://www.lib.kth.se/abs98/moyr1214.pdf.
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Moyroud, François. "Fluid-structure integrated computational methods for turbomachinery blade flutter and forced response predictions." Lyon, INSA, 1998. http://www.theses.fr/1998ISAL0101.
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Les ensembles disque-aubes des turbomachines modernes sont amenés à satisfaire des critères stricts en termes de stabilité aéroélastique et de réponse forcée. L'objectif de cette thèse est d'utiliser et de développer des techniques de modélisation, capables de prédire le phénomène de flottement et de quantifier les amplitudes de résonance des aubages de turbomachine. Pour le flottement, deux méthodes d'analyse aéroélastique sont considérées: la méthode énergétique (approche fluidestructure non-couplée) et le schéma de couplage modal (approche fluide-structure couplée). Ces modèles ont été installés dans le code de calcul STRUFLO qui offre des outils d'interface performants pour coupler divers codes de calcul. Des méthodes spécifiques sont utilisées afin de combiner plusieurs types d'analyses fluide et structure, et ainsi de progresser dans le sens d'un traitement général des interactions fluide-structure. A cet effet, le schéma de couplage modal est adapté pour être compatible avec des analyses modales d'aube seule ainsi que des analyses modales d'ensemble disque-aubes avec ou sans symétrie cyclique. Un maillage d'interface est utilisé pour résoudre les problèmes liés à l'incompatibilité des maillages fluide et structure à l'interface et une méthode d'interpolation/extrapolation permet de transférer les modes de vibration d'aube et les champs de pression instationnaire, du maillage structure au maillage aérodynamique et vice versa. Le désaccordage structure est l'une des caractéristiques pouvant considérablement modifier la stabilité aéroélastique et les amplitudes de résonance des aubages. A cet effet, deux méthodes de réduction ont été étudiées afin d'autoriser des analyses modales et de réponse forcée d'ensemble disque-aubes complet. Les techniques développées sont appliquées à l'étude des comportements dynamiques, aérodynamiques et aéroélastiques du fan transonique NASA Rotor 67, d'un fan transonique avec nageoires et d'un fan subsonique à large cordeThe lightweight, high performance bladed-disks used in today's aeroengines must meet strict standards in terms of aeroelastic stability and resonant response characteristics. The research presented in this thesis is directed toward improved prediction and understanding of blade flutters and forced response problems in turbomachines. To address the blade flutter problem, two aeroelastic analysis methods are considered: the energy method (fluid-structure uncoupled approach) and the modal aeroelastic coupling scheme (fluid-structure coupled approach). The two methods have been implemented in the STRUFLO master code which is designed to provide fluid-structure interfaces for a library of structural and flow solvers. Especially tailored methods are used to couple or interface a wide range of structural and aerodynamic analyses. First, the modal aeroelastic coupling scheme is extended to deal with single blade, cyclic symmetric and full assembly modal analyses as weil as single and multiple blade passage unsteady aerodynamic analyses. Second, an interfacing grid technique is proposed to circumvent problems due to the presence of non-conforming fluid and structural grids at the interface. Finally, a grid-to-grid interpolation/extrapolation scheme is used to transfer blade mode shapes and blade surface unsteady pressures from the structural grid to the aerodynamic grid and vice versa. One structural characteristic of bladed-disks that can significantly impact bath on the aeroelastic stability and the resonant response is that of structural mistuning. With this respect, two reduction methods have been developed to perform full assembly modal analyses and forced response analyses. Various numerical applications are proposed to illustrate the applicability of the above mentioned methods including structural dynamic, aerodynamic and aeroelastic analyses of the NASA Rotor 67 unshrouded transonic fan, a shrouded transonic fan and a subsonic wide chard fan
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Mata, Sanjay. "A fast generalized single-passage method for multi-blade row forced response and flutter." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523742.
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Richards, Phillip W. "Design strategies for rotorcraft blades and HALE aircraft wings applied to damage tolerant wind turbine blade design." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53488.
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Offshore wind power production is an attractive clean energy option, but the difficulty of access can lead to expensive and rare opportunities for maintenance. Smart loads management (controls) are investigated for their potential to increase the fatigue life of damaged offshore wind turbine rotor blades. This study will consider two commonly encountered damage types for wind turbine blades, the trailing edge disbond (bond line failure) and shear web disbond, and show how 3D finite element modeling can be used to quantify the effect of operations and control strategies designed to extend the fatigue life of damaged blades.
Modern wind turbine blades are advanced composite structures, and blade optimization problems can be complex with many structural design variables and a wide variety of aeroelastic design requirements. The multi-level design method is an aeroelastic structural design technique for beam-like structures in which the general design problem is divided into a 1D beam optimization and a 2D section optimization. As a demonstration of aeroelastic design, the multi-level design method is demonstrated for the internal structural design of a modern composite rotor blade. Aeroelastic design involves optimization of system geometry features as well as internal features, and this is demonstrated in the design of a flying wing aircraft. Control methods such as feedback control also have the capability alleviate aeroelastic design requirements and this is also demonstrated in the flying wing aircraft example.
In the case of damaged wind turbine blades, load mitigation control strategies have the potential to mitigate the effects of damage, and allow partial operation to avoid shutdown. The load mitigation strategies will be demonstrated for a representative state-of-the-art wind turbine (126m rotor diameter). An economic incentive will be provided for the proposed operations strategies, in terms of weighing the cost and risk of implementation against the benefits of increased revenue due to operation of damaged turbines. The industry trend in wind turbine design is moving towards very large blades, causing the basic design criterion to change as aeroelastic effects become more important. An ongoing 100 m blade (205 m rotor diameter) design effort intends to investigate these design challenges. As a part of that effort, this thesis will investigate damage tolerant design strategies to ensure next-generation blades are more reliable.
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Jinghe, Ren. "Development of a Shrouded SteamTurbine Flutter Test Case." Thesis, KTH, Kraft- och värmeteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-225857.
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A shrouded blade was designed as a test case for flutter analysis of steam turbine. Flutter is a self-excitedvibration. It can lead to dramatic blade loss and high-cycle fatigue. Shrouded blade is more complicated onflutter analysis, because the mode shapes are more complex with bending and torsion components atdifferent phases. Moreover, the blade mode shape and frequency also vary with nodal diameter. Lack ofopen resource of shrouded blade, there were less researches about shrouded blade test case on flutter. The initial blade geometry was from Di Qi’s 3D free standing blade test case. The material of the blade isTitanium. The aim of current study is to design a 3D test case for realistic shrouded blade flutter analysis. The geometryof the proposed shrouded blade test case was fully described in this thesis report. ANSYS ICEM was usedfor presenting the geometry and generating mesh. ANSYS APDL was used for structural analysis.Parameters of shroud parts were based on literature reviews and engineers’ general suggestions. The modeshapes for the first family of modes were calculated and reported.Ett höljeblad utformades som ett testfall för fladderanalys av ångturbin. Flutter är en självupphetsadvibration. Det kan leda till dramatisk bladförlust och högcykelutmattning. Höljeblad är mer kompliceratvid fladderanalys, eftersom modeformerna är mer komplexa med böjnings- och torsionskomponenter iolika faser. Dessutom varierar bladformsformen och frekvensen också med noddiameter. Brist på öppenresurs av höljet blad, det fanns mindre undersökningar om höljet blad test fall på flutter. Den ursprungligabladgeometrin var från Di Qis 3D frittstående bladprovfall. Bladets material är titan. Syftet med den aktuella studien är att designa ett 3D-testfall för realistisk hävd bladflöjtsanalys. Geometrinhos det föreslagna höljet av bladsprov beskrivs fullständigt i denna avhandlingsrapport. ANSYS ICEManvändes för att presentera geometrin och det genererande nätet. ANSYS APDL användes för strukturellanalys. Parametrar av höljesdelar baserades på litteraturrecensioner och ingenjörers allmänna förslag.Modeshistorierna för den första familjen av lägen beräknades och rapporterades.
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Monaco, Lucio. "PARAMETRIC STUDY OF THE EFFECT OF BLADE SHAPE ON THE PERFORMANCE OF TURBOMACHINERY CASCADES : PART III A: AERODYNAMIC DAMPING BEHAVIOUR – COMPRESSOR PROFILES." Thesis, KTH, Kraft- och värmeteknologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-131210.
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Vasilescu, Roxana. "Helicopter blade tip vortex modifications in hover using piezoelectrically modulated blowing." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-11192004-165246/unrestricted/vasilescu%5Froxana%5F200412%5Fphd.pdf.
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Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2005.Dancila, Stefan, Committee Chair ; Sankar, Lakshmi, Committee Member ; Ruzzene, Massimo, Committee Member ; Smith, Marilyn, Committee Member ; Yu, Yung, Committee Member. Vita. Includes bibliographical references.
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Sanz, Luengo Antonio. "Experimental Investigation of the Influence of Local Flow Features on the Aerodynamic Damping of an Oscillating Blade Row." Licentiate thesis, KTH, Kraft- och värmeteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145179.
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The general trend of efficiency increase, weight and noise reduction has derived in the design of more slender, loaded, and 3D shaped blades. This has a significant impact on the stability of fan, and low pressure turbine blades, which are more prone to aeroelastic phenomena such as flutter. The flutter phenomenon is a self-excited, self-sustained unstable vibration produced by the interaction of flow and structure. These working conditions will induce either blade overload, or High Cycle Fatigue (HCF) produced by Limited Cycle Oscillation (LCO). The main objectives of the present work are on the investigation of the aeroelastic properties of a high-lift low-pressure in the light of the local flow features present in such profiles, in nominal and extreme off-design conditions both in high and low subsonic Mach number, for three dif-ferent rigid body modes. In addition, the validity of the linearity assump-tion of the influence coefficient technique has also been investigated, in order to expand the understanding of the physical limits of this assumption. This work has been designed as experimental investigation in the influence coefficient domain focused on a high-lift low-pressure turbine designed by ITP within the framework of the European FP7 project FU-TURE. These experiments have been carried out in the Aeroelastic test rig (AETR), at KTH Stockholm, which consist of an instrumented annular sector cascade with a single oscillating blade. The results acquired have been supported by numerical results provided by a non-propietary commercial software package (ANSYS CFX). The results suggest that the typical three-dimensional effects associated secondary flow features and tip leakage flows have a significant influence on the aeroelastic performance and the cascade stability. However the major influence appears as a consequence of the separation surface on the pressure side which appears at extreme off-design operating conditions. The contribution to stability of this local feature depend on the oscillation mode showing for the axial and torsion mode a neutral stability contribution, which is directly associated with the geometrical properties of the cascade. However, on the circumferential mode this separation surface has a stabilizing effect much more independent of the blade geometry. The study of the linearity assumption of the influence coefficient domain has revealed, that an apparent linear relation between the integrated unsteady response and the vibrational amplitude, does not necessary imply that the local unsteady response is linear with respect to the oscillation amplitude. The results also suggest that the validity of the linearity as-sumption is more sensitive to high oscillation amplitudes at high Mach conditions.QC 20140609
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Sun, Tianrui. "Improved Flutter Prediction for Turbomachinery Blades with Tip Clearance Flows." Licentiate thesis, KTH, Energiteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-233770.
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Recent design trends in steam turbines strive for high aerodynamic loading and high aspect ratio to meet the demand of higher efficiency. These design trends together with the low structural frequency in last stage steam turbines increase the susceptibility of the turbine blades to flutter. Flutter is the self-excited and self-sustained aeroelastic instability phenomenon, which can result in rapid growth of blade vibration amplitude and eventually blade failure in a short period of time unless adequately damped. To prevent the occurrences of flutter before the operation of new steam turbines, a compromise between aeroelastic stability and stage efficiency has to be made in the steam turbine design process. Due to the high uncertainty in present flutter prediction methods, engineers use large safety margins in predicting flutter which can rule out designs with higher efficiency. The ability to predict flutter more accurately will allow engineers to push the design envelope with greater confidence and possibly create more efficient steam turbines. The present work aims to investigate the influence of tip clearance flow on the prediction of steam turbine flutter characteristics. Tip clearance flow effect is one of the critical factors in flutter analysis for the majority of aerodynamic work is done near the blade tip. Analysis of the impact of tip clearance flow on steam turbine flutter characteristics is therefore needed to formulate a more accurate aeroelastic stability prediction method in the design phase.Besides the tip leakage vortex, the induced vortices in the tip clearance flow can also influence blade flutter characteristics. However, the spatial distribution of the induced vortices cannot be resolved by URANS method for the limitation of turbulence models. The Detached-Eddy Simulation (DES) calculation is thus applied on a realistic-scale last stage steam turbine model to analyze the structure of induced vortices in the tip region. The influence of the tip leakage vortex and the induced vortices on flutter prediction are analyzed separately. The KTH Steam Turbine Flutter Test Case is used in the flutter analysis as a typical realistic-scale last stage steam turbine model. The energy method based on 3D unsteady CFD calculation is applied in the flutter analysis. Two CFD solvers, an in-house code LUFT and a commercial software ANSYS CFX, are used in the flutter analysis as verification of each other. The influence of tip leakage vortex on the steam turbine flutter prediction is analyzed by comparing the aeroelastic stability of two models: one with the tip gap and the other without the tip gap. Comparison between the flutter characteristics predicted by URANS and DES approaches is analyzed to investigate the influence of the induced vortices on blade flutter characteristics. The multiple induced vortices and their relative rotation around the tip leakage vortex in the KTH Steam Turbine Flutter Test Case are resolved by DES but not by URANS simulations. Both tip leakage vortex and induced vortices have an influence on blade loading on the rear half of the suction side near the blade tip. The flutter analysis results suggest that the tip clearance flow has a significant influence on blade aerodynamic damping at the least stable interblade phase angle (IBPA), while its influence on the overall shape of the damping curve is minor. At the least stable IBPA, the tip leakage vortex shows a stabilization effect on rotor aeroelastic stabilities while the induced vortices show a destabilization effect on it. Meanwhile, a non-linear unsteady flow behavior is observed due to the streamwise motion of induced vortices during blade oscillation, which phenomenon is only resolved in DES results.
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Couch, Mark A. "A three-dimensional flutter theory for rotor blades with trailing-edge flaps." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5fCouch%5FPhD.pdf.
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Thesis (Ph. D. in Aeronautical and Astronautical Engineering)--Naval Postgraduate School, June 2003.Dissertation supervisor and advisor: E. Roberts Wood. Includes bibliographical references (p. 205-210). Also available online.
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Forhad, Md Moinul Islam. "Robustness analysis for turbomachinery stall flutter." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4894.
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As compared with other robustness analysis tools, such as Hsubscript inf], the Mu analysis is less conservative and can handle both structured and unstructured perturbations. Finally, Genetic Algorithm is used as an optimization tool to find ideal parameters that will ensure best performance in terms of damping out flutter. Simulation results show that the procedure described in this thesis can be effective in studying the flutter stability margin and can be used to guide the gas turbine blade design.; Flutter is an aeroelastic instability phenomenon that can result either in serious damage or complete destruction of a gas turbine blade structure due to high cycle fatigue. Although 90% of potential high cycle fatigue occurrences are uncovered during engine development, the remaining 10% stand for one third of the total engine development costs. Field experience has shown that during the last decades as much as 46% of fighter aircrafts were not mission-capable in certain periods due to high cycle fatigue related mishaps. To assure a reliable and safe operation, potential for blade flutter must be eliminated from the turbomachinery stages. However, even the most computationally intensive higher order models of today are not able to predict flutter accurately. Moreover, there are uncertainties in the operational environment, and gas turbine parts degrade over time due to fouling, erosion and corrosion resulting in parametric uncertainties. Therefore, it is essential to design engines that are robust with respect to the possible uncertainties. In this thesis, the robustness of an axial compressor blade design is studied with respect to parametric uncertainties through the Mu analysis. The nominal flutter model is adopted from (9). This model was derived by matching a two dimensional incompressible flow field across the flexible rotor and the rigid stator. The aerodynamic load on the blade is derived via the control volume analysis. For use in the Mu analysis, first the model originally described by a set of partial differential equations is reduced to ordinary differential equations by the Fourier series based collocation method. After that, the nominal model is obtained by linearizing the achieved non-linear ordinary differential equations. The uncertainties coming from the modeling assumptions and imperfectly known parameters and coefficients are all modeled as parametric uncertainties through the Monte Carlo simulation.ID: 030423207; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.)--University of Central Florida, 2011.; Includes bibliographical references (p. 44-47).
M.S.
Masters
Mechanical, Materials, and Aerospace Engineering
Engineering and Computer Science
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Groß, Johann [Verfasser]. "Numerical analysis of flutter-induced multi-wave vibrations of bladed disks with tip-shroud friction / Johann Groß." München : Verlag Dr. Hut, 2020. http://d-nb.info/1219475920/34.
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Klíma, Petr. "Parní turbina rychloběžná kondenzační." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231803.
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ith one controlled extraction and one uncontrolled extraction, calculation of the flow channel at all stage, design and calculation of the regulation valve and create connection diagram of steam turbine and air cooled condenser. At the beginning of this work is an overview of manufacturers of steam turbines and their unified products. Master thesis was developer with G-Team, a.s. as using calculations and the instructions given in the recommended literature with supporting CFD simulations to determine the loss coefficients and FEA simulations to determine the eigenfrequencies blades.
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Cantoni, Lorenzo. "Load Control Aerodynamics in Offshore Wind Turbines." Thesis, KTH, Kraft- och värmeteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291417.
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Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade.På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.
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陳其志. "Investigation of turbomachinery rotor blade flutter." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/38093533904129806741.
Full textAbstract:
碩士國立清華大學
動力機械工程學系
90
A frequent cause of turbomachinery rotor blade failure, including jet engines, aircraft engines and turbogenerators, is excessive vibration due to flutter or forced response. One method for dealing with this problem is to increase blade structural damping, using either tip or mid-span shroud design. Unfortunately, most existing aeroelastic analyses deal with blade alone model, which can not be used for system mode analysis. Therefore, judgements based on past experience are used to determine the acceptability of a shrouded blade design. A system approach analysis will be developed to predict shrouded blade flutter. This analysis will provide a system approach, over and above the standard blade alone approach, for predicting potential aeroelastic problems. Using the blade natural frequencies and mode shapes from both measurements and a finite element model, the unsteady aerodynamic forces of the system mode will be calculated using the blade surface supersonic, transonic, and subsonic flow field. A system flutter analysis will then be performed using a modal solution to determine the stability of the system. Besides using the experimental data to verify the finite element blade model, a non-shrouded blade flutter analysis will be used to verify the system mode flutter analysis. Also, we will use this method to study the major mechanism causing shrouded rotor blade to flutter in some specific modes including bending and torsion modes. Shrouded rotor blade design has been widely used in fans, compressors, and turbines. The proposed research method can remedy the current deficiency in shrouded rotor blade design and also can provide guidance for shrouded blade maintenance and life management.
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Bhat, Shantanu. "Study Of Stall Flutter Of An Isolated Blade In A Low Reynolds Number Incompressible Flow." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2443.
Full textAbstract:
Highly-loaded turbomachine blades can stall under off-design conditions. In this regime, the flow can separate close to the leading edge of the blade in a periodic manner that can lead to blade vibrations, commonly referred to as stall flutter. Prior experimental studies on stall flutter have been at large Re (Re ~ 106). In the present work, motivated by applications in Unmanned Air Vehicles (UAV) and Micro Air Vehicles (MAV), we study experimentally the forces and flow fields around an oscillating blade at low Re (Re ~ 3 x 104). At these low Re, the flow even over the stationary blade can be quite different.
We experimentally study the propensity of an isolated symmetric and cambered blade (with chord c) to undergo self-excited oscillations at high angles of attack and at low Reynolds numbers (Re ~ 30, 000). We force the blade, placed at large mean angle of attack, to undergo small amplitude pitch oscillations and measure the unsteady loads on the blade. From the measured loads, the direction and magnitude of energy transfer to/from the blade is calculated. Systematic measurements have been made for varying mean blade incidence angles and for different excitation amplitudes and frequencies (f). These measurements indicate that post stall there is a possibility of excitation of the blade over a range of Strouhal Numbers (St = fc/U) with the magnitude of the exciting energy varying with amplitude, frequency and mean incidence angles. In particular, the curves for the magnitude of the exciting energy against Strouhal number (St) are found to shift to higher St values as the mean angle of attack is increased. We perform the same set of experiments on two different blade shapes, namely NACA 0012 and a compressor blade profile, SC10. Both blade profiles show qualitatively similar phenomena.
The flow around both the stationary and oscillating blades is studied through Particle Image Velocimetry (PIV). PIV measurements on the stationary blade show the gradual shift of the flow separation point towards the leading edge with increasing angle of attack, which occurs at these low Re. From PIV measurements on an oscillating blade near stall, we present the flow field around the blade at different phases of the blade oscillation. These show that the boundary layer separates from the leading edge forming a shear layer, which flaps with respect to the blade. As the Strouhal number is varied, the phase between the flapping shear layer and the blade appears to change. This is likely to be the reason for the observed change in the sign of the energy transfer between the flow and the blade that is responsible for stall flutter.
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Jha, Sourabh Kumar. "Stall Flutter of a Cascade of Blades at Low Reynolds Number." Thesis, 2013. http://hdl.handle.net/2005/2865.
Full textAbstract:
Due to the requirements for high blade loading, modern turbo‐machine blades operate very close to the stall regime. This can lead to flow separation with periodic shedding of vortices, which could lead to self induced oscillations or stall flutter of the blades. Previous studies on stall flutter have focused on flows at high Reynolds number (Re ~ 106). The Reynolds numbers for fans/propellers of Micro Aerial Vehicles (MAVs), high altitude turbofans and small wind turbines are substantially lower (Re < 105). Aerodynamic characteristics of flows at such low Re is significantly different from those at high Re, due in part to the early separation of the flow and possible formation of laminar separation bubbles (LSB). The present study is targeted towards study of stall flutter in a cascade of blades at low Re.
We experimentally study stall flutter of a cascade of symmetric NACA 0012 blades at low Reynolds number (Re ~ 30, 000) through forced sinusoidal pitching of the blades about mean angles of incidences close to stall. The experimental arrangement permits variations of the inter‐blade phase (σ) in addition to the oscillation frequency (f) and amplitude; the inter‐blade phase angle (σ) being the phase difference between the motions of adjacent blades in the cascade. The unsteady moments on the central blade in the cascade are directly measured, and used to calculate the energy transfer from the flow to the blade. This energy transfer is used to predict the propensity of the blades to undergo self‐induced oscillations or stall flutter. Experiments are also conducted on an isolated blade in addition to the cascade.
A variety of parameters can influence stall flutter in a cascade, namely the oscillation frequency (f), the mean angle of incidence, and the inter‐blade phase angle (σ). The measurements show that there exists a range of reduced frequencies, k (=πfc/U, c being the chord length of the blade and U being the free stream velocity), where the energy transfer from the flow to the blade is positive, which indicates that the flow can excite the blade. Above and below this range, the energy transfer is negative indicating that blade excitations, if any, will get damped. This range of excitation is found to depend upon the mean angle of incidence, with shifts towards higher values of k as the mean angle of incidence increases. An important parameter for cascades, which is absent in the isolated blade case is the inter‐blade phase angle (σ). An excitation regime is observed only for σ values between ‐450 and 900, with the value of excitation being maximum for σ of 900. Time traces of the measured moment were found to be non‐sinusoidal in the excitation regime, whereas they appear to be sinusoidal in the damping regime.
Stall flutter in a cascade has differences when compared with an isolated blade. For the cascade, the maximum value of excitation (positive energy transfer) is found to be an order of magnitude lower compared to the isolated blade case. Further, for similar values of mean incidence angle, the range of excitation is at lower reduced frequencies for a cascade when compared with an isolated blade. A comparison with un‐stalled or classical flutter in a cascade at high Re, shows that the inter‐blade phase angle is a major factor governing flutter in both cases. Some differences are observed as well, which appear to be due to stalled flow and low Re.
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Chin, Xiang-Rui, and 秦祥睿. "Analysis of Steam Turbine Blade Flutter in Power Facility." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/62437399335175833895.
Full text
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Ladge, Shruti. "Experimental Study of Stability Limits for Slender Wind Turbine Blades." 2012. https://scholarworks.umass.edu/theses/921.
Full textAbstract:
There is a growing interest in extracting more power per turbine by increasing the rotor size in offshore wind turbines. As a result, the turbine blades will become longer and therefore more flexible and a flexible blade is susceptible to flow-induced instabilities, such as classical flutter. In order to design and build stable large wind turbine blades, the onset of instability should be considered in the design process. To observe flow-induced instabilities in wind turbine blades, a small-scale flexible blade was built based on NREL 5MW reference wind turbine blade. The blade was placed in the test section of a wind tunnel and its tip displacement was measured using a non-contacting displacement measurement device. The blade was non-rotating and was subjected to uniform incoming flow. For a range of blade angles of attack, instability was observed beyond a critical wind speed. The amplitude of oscillations increases for wind speeds higher than the critical speed, and the frequency of oscillations remains constant. Flow visualizations and force measurements are conducted and the influence of various system parameters including the angle of attack and the blade twist was examined.
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Kumar, Vijay. "Viscous Vortex Method Simulations of Stall Flutter of an Isolated Airfoil at Low Reynolds Numbers." Thesis, 2013. http://etd.iisc.ernet.in/handle/2005/2814.
Full textAbstract:
The flow field and forces on an isolated oscillating NACA 0012 airfoil in a uniform flow is studied using viscous vortex particle method. The simulations are carried out at very low chord (c) based Reynolds number (Re=1000), motivated by the current interest in development of Micro Air Vehicles (MAV). The airfoil is forced to oscillate in both heave and pitch at different normalized oscillation frequencies (f), which is represented by the non-dimensional reduced frequency fc/U).( From the unsteady loading on the airfoil, the net energy transfer to the airfoil is calculated to determine the propensity for the airfoil to undergo self-induced oscillations or flutter at these very low Reynolds numbers. The simulations are carried out using a viscous vortex particle method
that utilizes discrete vortex elements to represent the vorticity in the flow field. After validation of the code against test cases in the literature, simulations are first carried out for the stationary airfoil at different angles of attack, which shows the stall characteristics
of the airfoil at this very low Reynolds numbers.
For the airfoil oscillating in heave, the airfoil is forced to oscillate at different reduced frequencies at a large angle of attack in the stall regime. The unsteady loading on the blade is obtained at different reduced frequencies. This is used to calculate the net energy transfer to the airfoil from the flow, which is found to be negative in all cases studied. This implies that stall flutter or self-induced oscillations are not possible under the given heave conditions. The wake vorticity dynamics is presented for the different reduced frequencies, which show that the leading edge vortex dynamics is progressively
more complex as the reduced frequency is increased from small values. For the airfoil oscillating in pitch, the airfoil is forced to oscillate about a large mean angle of attack corresponding to the stall regime. The unsteady moment on the blade is obtained at different reduced frequencies, and this is used to calculate the net energy transfer to the airfoil from the flow, which is found to be positive in all cases studied. This implies that stall flutter or self-induced oscillations are possible in the pitch mode, unlike in the heave case. The wake vorticity dynamics for this case is found to be relatively simple compared to that in heave. The results of the present simulations are broadly in agreement with earlier stall flutter studies at higher Reynolds numbers that show that stall flutter does not occur in the heave mode, but can occur in the pitch mode. The main difference in the present very low Reynolds number case appears to be the broader extent of the excitation region in the pitch mode compared to large Re cases studied earlier.
region in the pitch mode compared to large Re cases studied earlier.
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Sicard, Jérôme. "Investigation of an extremely flexible stowable rotor for micro-helicopters." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-05-3587.
Full textAbstract:
This thesis describes the analysis, fabrication and testing of a rotor with extremely flexible blades, focusing on application to a micro-helicopter. The flexibility
of the rotor blades is such that they can be rolled into a compact volume and stowed inside the rotor hub. Stiffening and stabilization of the rotor is enabled by centrifugal forces acting on a tip mass. Centrifugal effects such as bifilar and propeller moments are investigated and the torsional equation of motion for a blade
with low torsional stiffness is derived. Criteria for the design of the tip mass are also derived and it is chosen that the center of gravity of each blade section must be located ahead of the aerodynamic center.
This thesis presents the design of 18-inch diameter two-bladed rotors having untwisted circular arc airfoil profile with constant chord. A systematic experimental
investigation of the effect of various blade parameters on the stability of the rotor is conducted in hover and forward flight. These parameters include blade flexibility in bending and torsion, blade planform and mass distribution. Accordingly, several
sets of blades varying these parameters are constructed and tested. It is observed that rotational speed and collective pitch angles have a significant effect on rotor stability. In addition, forward flight velocity is found to increase the blade stability.
Next, the performance of flexible rotors is measured. In particular, they are compared to the performance of a rotor with rigid blades having an identical planform
and airfoil section. It is found that the flexible blades are highly twisted during operation, resulting in a decreased efficiency compared to the rigid rotor blades. This induced twist is attributed to an unfavorable combination of tip body design
and the propeller moment acting on it. Consequently, the blade design is modified and three different approaches to passively tailor the spanwise twist distribution for
improved efficiency are investigated. In a first approach, extension-torsion composite material coupling is analyzed and it is shown that the centrifugal force acting on the tip mass is not large enough to balance the nose-down twist due to the propeller moment. The second concept makes use of the propeller moment acting on the tip mass located at an index angle to produce an untwisted blade in hover. It is constructed and tested. The result is an untwisted 18-inch diameter rotor whose maximum Figure of Merit is equal to 0.51 at a blade loading of 0.14. Moreover, this rotor is found to be stable for any collective pitch angle greater than 11 degrees. Finally, in a third approach, addition of a trailing-edge flap at the tip of the flexible rotor blade is investigated. This design is found to have a lower maximum Figure
of Merit than that of an identical flexible rotor without a flap. However, addition of this control surface resulted in a stable rotor for any value of collective pitch angle. Future plans for increasing the efficiency of the flexible rotor blades and for developing an analytical model are described.text
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Chang, Lin-Ya, and 張琳雅. "Flutter Analysis of Shrouded Steam Turbine Blades." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/38546575713691226146.
Full textAbstract:
碩士國立清華大學
動力機械工程學系
97
All the rotor blades in turbo-machinery, including turbojet engines and turbo-generators, have vibration problems. The blades are damaged because of vibrations caused by flutter or forced response. Generally, the shrouded design of the turbine blades is used to raise the structural damping and strength of the rotor blades. This research is primarily focused on vibration phenomenon of steam turbine’s shrouded rotor blades. Because the Hamoaka Nuclear Power Station No. 5 occurred some phenomenon like flutter, and the low pressure steam turbines of Hamoaka Nuclear Power Station No. 5 and Taipower’s Lung-Men Nuclear Power Plant Units 1&2 are both the Advanced Boiling Water Reactors, the research begin to analysis the rotor blades of the low pressure steam turbine. A complete system approach has been set up to study the main mechanism of shrouded rotor blade vibration. The research starts with the dynamic structural properties of the blades, the properties along with flow fields were used to calculate the unsteady steam load caused by structural movement. Because the design of shrouded rotor blades will cause the entire rotor into system mode shapes, it is necessary to use cyclic symmetry along with the modal flutter analysis system to calculate the aero damping of the shrouded dynamic blade system and to determine its flutter instability of the low pressure steam turbine of Taipower’s Lung-Men Nuclear Power Plant. This study will be based on a Taipower plant case to investigate the flutter boundary of steam turbine rotor blades under different operating conditions. However, for the bending and torsion combined system modes, the single mode analysis can be misleading. From the complex mode analyzed results, it was demonstrated that the mode shape, the characteristic of flow field, and the structural damping play an important role in determining the blade flutter stability. And there is flutter phenomenon in supersonic flow field, it may result in blades failure. So, it’s necessary to prevent this condition to improve the system safety.
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Shapiro, Benjamin. "Passive control of flutter and forced response in bladed disks via mistuning." Thesis, 1999. https://thesis.library.caltech.edu/784/1/Shapiro_b_1999.pdf.
Full textAbstract:
Mistuning or blade to blade variation in jet-engine bladed-disks can lead to large changes in engine performance. Even the small random mistuning associated with manufacturing tolerances can significantly change both stability boundaries and forced response. This thesis addresses two questions. Analysis: given any mistuning (random or intentional), what is the resulting change in performance? And passive control: can intentional mistuning be used to improve stability and forced response in a robust manner?
A general framework based on symmetry arguments and eigenvalue/vector perturbations is presented to answer both questions. Symmetry constrains all facets of mistuning behaviour and provides simplifications for both the analysis and control problems. This is combined with the eigenvalue/vector perturbation which captures the nonlinear mistuning dependence and solves the analysis problem. It is shown that intentional mistuning can provide robust damping and so guarantee improved stability and forced response under fixed manufacturing tolerances. Results are demonstrated on a high-fidelity low-order model derived from computational-fluid-dynamic data.