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Evgeny Petrov - One of the best experts on this subject based on the ideXlab platform.

  • Sensitivity Analysis of High-Frequency Forced Response for Mistuned Bladed Discs Based on High-Fidelity Models
    Volume 7A: Structures and Dynamics, 2016
    Co-Authors: Yuanqiu Tan, Chaoping Zang, Biao Zhou, Yongliang Duan, Evgeny Petrov
    Abstract:

    This paper proposes an effective method for sensitivity analysis of Forced Response of bladed discs to blade mistuning. The numerical studies of Forced Response of a turbine bladed disc vibrating in the frequency ranges corresponding to resonances with higher modes are also presented. The blade mistuning is modelled by specially defined mistuning matrices used for simulating experimentally measured scatter of blade natural frequencies. Based on this method, the sensitivity of Forced Response amplitude levels are studied for displacements and stress levels for a realistic model of a bladed disc. The effective Response surface techniques are developed for explicit representation of the mistuned Forced Response as a function of blade mistuning elements.

  • Reduction of Forced Response Levels for Bladed Disks by Mistuning: Overview of the Phenomenon
    Journal of Engineering for Gas Turbines and Power, 2011
    Co-Authors: Evgeny Petrov
    Abstract:

    The newly revealed phenomenon of reduction of Forced Response levels in a mistuned bladed disk to levels significantly (e.g., by a factor of 2 and more) lower than that of its tuned counterpart is studied in detail on an example of a realistic bladed disk. Statistical properties of the amplification factor of the mistuned Forced Response calculated with aero-effects included have been studied for cases of random blade mistuning and for mistuned blade rearrangements. The optimization search for the best mistuning patterns providing maximum Forced Response reduction effect have been performed and the robustness of the optimum mistuning patterns has been demonstrated. The combined effect of the aerodynamic and structural damping on the Response reduction is assessed. It is shown that the new phenomenon is of major practical significance and has to be taken into account in analysis of the Forced Response and design decisions.

  • Analysis of sensitivity and robustness of Forced Response for nonlinear dynamic structures
    Mechanical Systems and Signal Processing, 2009
    Co-Authors: Evgeny Petrov
    Abstract:

    An effective method is developed for calculation of the sensitivity and robustness of the Forced Response levels for strongly nonlinear structures. The sensitivity coefficients are determined with respect to parameters of friction contact interfaces, parameters of linear components of an assembled structure, frequency and level of excitation forces. Equations for determination of first- and second-order sensitivity coefficients of the Forced Response are derived analytically from a nonlinear multiharmonic equation of motion. The analytical derivation allows accurate and fast evaluation of the sensitivity coefficients. The sensitivity coefficients are calculated in frequency domain for each excitation frequency over the frequency range analysed simultaneously with the force Response levels. The developed highly efficient method allows calculation of sensitivity characteristics without a noticeable increase of the computation time in addition to the time required for the Forced Response calculation. A measure of the Forced Response robustness is introduced. Sensitivity-based method for assessment of the Forced Response robustness for given ranges of uncertainty of structural and operating parameters is proposed. The methodology developed is illustrated on a set of problems including cases of Forced Response analysis for realistic strongly nonlinear gas-turbine structures.

  • A Sensitivity-Based Method for Direct Stochastic Analysis of Nonlinear Forced Response for Bladed Disks With Friction Interfaces
    Journal of Engineering for Gas Turbines and Power, 2008
    Co-Authors: Evgeny Petrov
    Abstract:

    An efficient method is developed to calculate stochastic and uncertainty characteristics of Forced Response for nonlinear vibrations of bladed disks with friction and gap contact interfaces. Uncertainty ranges, statistical characteristics, and probability density functions for Forced Response levels are determined directly without any sampling procedure. The method uses approximations of the Forced Response level based on derived analytically and calculated extremely fast and accurately sensitivity coefficients of Forced Response with respect to friction contact interface parameters. The method effectiveness allows analysis of strongly nonlinear vibration of bladed disks using realistic large-scale finite element models. The method is implemented in a program code developed at Imperial College and numerical examples of application of the method for stochastic analysis of a realistic blisc with underplatform dampers are provided.

  • A Sensitivity-Based Method for Direct Stochastic Analysis of Nonlinear Forced Response for Bladed Discs With Friction Interfaces
    Volume 5: Turbo Expo 2007, 2007
    Co-Authors: Evgeny Petrov
    Abstract:

    An efficient method is developed to calculate stochastic and uncertainty characteristics of Forced Response for nonlinear vibrations of bladed discs with friction and gap contact interfaces. Uncertainty ranges, statistical characteristics and probability density functions for Forced Response levels are determined directly without any sampling procedure. The method uses approximations of the Forced Response level based on derived analytically and calculated extremely fast and accurately sensitivity coefficients of Forced Response with respect to friction contact interface parameters. The method effectiveness allows analysis of strongly nonlinear vibration of bladed discs using realistic large-scale FE element models. The method is implemented in a program code developed at Imperial College and numerical examples of application of the method for stochastic analysis of a realistic blisc with underplatform dampers are provided.Copyright © 2007 by ASME

Dishan Huang - One of the best experts on this subject based on the ideXlab platform.

  • Forced Response approach of a parametric vibration with a trigonometric series
    Mechanical Systems and Signal Processing, 2014
    Co-Authors: Dishan Huang
    Abstract:

    Abstract A Forced vibration problem with parametric stiffness is modeled by feedback structure in this manuscript, and the Forced Response is expressed as a special trigonometric series. The Forced Response of this problem is determined by algebraic equation. By applying harmonic balance and limitation operation, all coefficients of the harmonic components in the Forced Response solution are fully approached. The investigation result shows that the new approach has an advantage in the computational time and accuracy, and it is very significant for the theoretical research and engineering application in dealing with the problem of Forced parametric vibration.

  • Forced Response Approach to Predict Parametric Vibration
    2013
    Co-Authors: Dishan Huang
    Abstract:

    In this paper, forecast modelling based on modulation feedback is used to investigate the Forced Response of parametric vibration with a damper. The system is excited by both the periodic coefficient and external force terms, which have different periods. In this study, the Forced Response is expressed as a linear combination of harmonic components. By applying harmonic balance, the parametric equation is converted into a set of infinite-order linear algebraic equations. Then, by taking the limit to infinity, all coefficients of the harmonic components in the Forced Response are fully expanded into a series. The advantages of the presented approach are (1) the Forced Response expressed as a trigonometric series is easier to apply in practice and (2) all coefficients of the harmonic components can be determined by numerical computation. The accuracy of the proposed approach has been verified by comparing resulting phase diagram trajectories with those obtained by the standard Runge-Kutta method. The results show that the presented approach is suitable for the Forced Response approach and the nonlinear characterization of parametric vibration.

Jens Nipkau - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Mistuning and Damping on the Forced Response of a Compressor Blisk Rotor
    Volume 7B: Structures and Dynamics, 2015
    Co-Authors: Bernd Beirow, Arnold Kühhorn, Felix Figaschewsky, Jens Nipkau
    Abstract:

    The Forced Response of an E3E-type high pressure compressor blisk front rotor is analyzed with regard to intentional mistuning and its robustness towards additional random mistuning. Both a chosen alternating mistuning pattern and artificial mistuning patterns optimized concerning the Forced Response are considered. Focusing on three different blade modes, subset of nominal system mode-based reduced order models are employed to compute the Forced Response. The disk remains unchanged while the Young’s modulus of each blade is used to define the particular mistuning pattern. The well established aerodynamic influence coefficient technique is employed to model aeroelastic coupling and hence to consider the strongly mode- and inter blade phase angle-dependent aerodynamic damping contribution.It has been found that a reduction of the maximum Forced Response beyond that of the tuned reference can be achieved for particular mistuning patterns and all modes considered. This implies an exciting engine order which would cause a low nodal diameter mode in case of a tuned blisk. At best a nearly 50% reduction of maximum Response magnitudes is computed for the fundamental bending mode and large mistuning. The solution proved to be robust towards additional random mistuning of reasonable magnitude, which is of particular interest with regard to a potential technical realization. In case of small mistuning as assumed for the first torsion and the longitudinal bending mode the advantage of achieving Response magnitudes beyond the tuned reference gets lost indeed, if random mistuning is superimposed. However, mostly a lower Response level is calculated compared to Responses obtained from models adjusted to mistuning determined by experiment.© 2015 ASME

  • Optimization-Aided Forced Response Analysis of a Mistuned Compressor Blisk
    Journal of Engineering for Gas Turbines and Power, 2014
    Co-Authors: Bernd Beirow, Thomas Giersch, Arnold Kühhorn, Jens Nipkau
    Abstract:

    The Forced Response of the first rotor of an E3E-type high pressure compressor blisk is analyzed with regard to varying mistuning, varying engine order excitations and the consideration of aeroelastic effects. For that purpose, SNM-based reduced order models are used in which the disk remains unchanged while the Young’s modulus of each blade is used to define experimentally adjusted as well as intentional mistuning patterns. The aerodynamic influence coefficient technique is employed to model aeroelastic interactions. Furthermore, based on optimization analyses and depending on the exciting EO and aerodynamic influences it is searched for the worst as well as the best mistuning distributions with respect to the maximum blade displacement. Genetic algorithms using blade stiffness variations as vector of design variables and the maximum blade displacement as objective function are applied. An allowed limit of the blades’ Young’s modulus standard deviation is formulated as secondary condition. In particular, the question is addressed if and how far the aeroelastic impact, mainly causing aerodynamic damping, combined with mistuning can even yield a reduction of the Forced Response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the inter-blade phase angle is the main driver for a possible Response attenuation considering the fundamental blade mode. The results of the optimization analyses are compared to the Forced Response due to real, experimentally determined frequency mistuning as well as intentional mistuning.Copyright © 2014 by Rolls-Royce Deutschland Ltd & Co KG

  • Optimization-Aided Forced Response Analysis of a Mistuned Compressor Blisk
    Volume 7B: Structures and Dynamics, 2014
    Co-Authors: Bernd Beirow, Thomas Giersch, Arnold Kühhorn, Jens Nipkau
    Abstract:

    The Forced Response of the first rotor of an E3E-type high pressure compressor blisk is analyzed with regard to varying mistuning, varying engine order excitations and the consideration of aeroelastic effects. For that purpose, SNM-based reduced order models are used in which the disk remains unchanged while the Young’s modulus of each blade is used to define experimentally adjusted as well as intentional mistuning patterns. The aerodynamic influence coefficient technique is employed to model aeroelastic interactions. Furthermore, based on optimization analyses and depending on the exciting EO and aerodynamic influences it is searched for the worst as well as the best mistuning distributions with respect to the maximum blade displacement. Genetic algorithms using blade stiffness variations as vector of design variables and the maximum blade displacement as objective function are applied. An allowed limit of the blades’ Young’s modulus standard deviation is formulated as secondary condition. In particular, the question is addressed if and how far the aeroelastic impact, mainly causing aerodynamic damping, combined with mistuning can even yield a reduction of the Forced Response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the inter-blade phase angle is the main driver for a possible Response attenuation considering the fundamental blade mode. The results of the optimization analyses are compared to the Forced Response due to real, experimentally determined frequency mistuning as well as intentional mistuning.

  • Forced Response Analysis of a Mistuned Compressor Blisk
    Volume 7B: Structures and Dynamics, 2013
    Co-Authors: Bernd Beirow, Thomas Giersch, Arnold Kühhorn, Jens Nipkau
    Abstract:

    The Forced Response of an E3E-type HPC-blisk front rotor is analyzed with regard to varying mistuning and the consideration of the fluid-structure interaction (FSI). For that purpose, a reduced order model is used in which the disk remains unchanged and mechanical properties of the blades namely stiffness and damping are adjusted to measured as well as intentional blade frequency mistuning distributions. The aerodynamic influence coefficient technique is employed to model the aeroelastics. Depending on the blade mode, the exciting engine order and aerodynamic influences it is sought for the worst mistuning distributions with respect to the maximum blade displacement based on optimization analyses. Genetic algorithms using blade alone frequencies as design variables are applied. The validity of the Whitehead-limit is assessed in this context. In particular, the question is addressed if and how far aeroelastic effects, mainly caused by aerodynamic damping, combined with mistuning can even cause a reduction of the Forced Response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the inter-blade phase angle is the main driver for a possible Response attenuation considering the fundamental as well as a higher blade mode. Furthermore, the differences to the blisk vibration Response without a consideration of the flow and an increase of the disk’s stiffness are discussed. Closing, the influence of pure damping mistuning is analyzed again using optimization.

Christophe Pierre - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of the combined effects of intentional and random mistuning on the Forced Response of bladed disks
    34th AIAA ASME SAE ASEE Joint Propulsion Conference and Exhibit, 1998
    Co-Authors: Matthew P. Castanier, Christophe Pierre
    Abstract:

    The maximum blade Forced Response amplitudes for mistuned bladed disks are generally much greater than those of their tuned counterparts. However, it is known that the ratio of mistuned to tuned maximum amplitudes — the amplitude magnification — is often largest at a relatively small level of mistuning. Increasing the level of mistuning beyond this critical value actually leads to a decrease in the amplitude magnification. In this study, the use of "intentional mistuning" to reduce the amplitude magnification of an industrial rotor is investigated. Intentional mistuning is introduced into a reduced order model of a 29-blade industrial rotor by varying the nominal blade stiffnesses in harmonic patterns. In addition to this intentional mistuning, the unavoidable, random mistuning of the blades is included in the model as usual. The individual and combined effects of intentional and random mistuning on the statistics of the Forced Response are examined. It is seen that intentional mistuning can greatly reduce the rotor's sensitivity to random mistuning. * Assistant Research Scientist, Department of Mechanical Engineering and Applied Mechanics. Member AIAA, Associate Member ASME. t Professor, Department of Mechanical Engineering and Applied Mechanics. Senior Member AIAA, Fellow ASME. Copyright © 1998 by Matthew P. Castanier. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. INTRODUCTION In general, the blades of a turbomachinery rotor are intended to be identical. However, there are always small, random deviations in the blade properties due to manufacturing tolerances, in-operation wear, and so forth. These blade-to-blade discrepancies are called mistuning. It is known that random mistuning in bladed disks can cause a significant increase in the Forced Response blade vibration amplitudes compared to the ideal (tuned) assembly [1-3]. The attendant increase in blade stresses can lead to premature fatigue of the blades. It is therefore of great interest to be able to predict and to reduce the maximum blade Forced Response amplitudes. It should be noted that the variable of interest is the largest Forced Response amplitude found for any blade when sweeping through the frequency range of interest. One can define an "amplitude magnification factor" as the ratio of the maximum mistuned Forced Response amplitude to the maximum tuned Forced Response amplitude. By normalizing with respect to the tuned system, this factor provides a quantitative measure of the detrimental impact of random mistuning. Several studies have demonstrated that the amplitude magnification tends to exhibit a peak value with respect to mistuning strength [4-7]. That is, the maximum Forced Response increases with increasing mistuning up to a certain level, but a further increase in-mistuning actually results in lower Forced Response amplitudes. This remarkable effect American Institute of Aeronautics and Astronautics of random mistuning has been demonstrated and explained in an analytical study [7], as well as documented in a case study of the industrial rotor considered here [8]. This peak amplitude phenomenon leads one to wonder whether "intentional mistuning" could be introduced into the design of a bladed disk, in order to reduce the adverse effects of random mistuning. This idea has been considered, either directly or indirectly, in a few studies. For instance, Ewins [9] discussed the possible advantages of bladed disk designs in which blades are grouped into "packets" of shrouded blades. This type of design introduces a form of mistuning, and Ewins explored the beneficial effects of "detuning" the Response of certain modes. Griffin and Hoosac [10] considered measuring the blade-alone natural frequencies and then placing the blades so that they alternated between those with higher and lower frequencies. Thus, an "alternate mistuning" pattern was achieved, and they observed some reduction in the Forced Response for a lumped parameter model of a bladed disk. However, they did not consider intentional mistuning in the design of the blades. Crawley and Hall [11] did consider deliberate mistuning in the blade design, as well as random mistuning, and they even found optimal patterns of intentional mistuning. However, the focus of their work was the aerodynamic stability of the rotor. More recently, Rzadkowski [12] investigated the transient nozzle excitation of mistuned bladed disks. By examining several configurations of a set of nominally different blades, Rzadkowski found that a random configuration led to the greatest increase in stresses, while an n-periodic blade arrangement was the best distribution in terms of minimizing the largest stresses. Yiu and Ewins [13] simulated many randomly mistuned realizations of a simple model of a 36-bladed disk, and they used Discrete Fourier Transforms to find the harmonic components of the best and worst mistuning patterns. However, they did not include intentional mistuning in the design. In this paper, the introduction of intentional mistuning into the nominal design of a rotor is considered. In particular, the effects on the maximum blade Forced Response amplitudes are investigated. A previous study by the authors [14] found that intentional mistuning could be used to reduce the Forced Response predicted for a simple lumped parameter model of a 12-bladed disk. Here, a reduced order model of a 29-blade industrial rotor [8] is employed to further investigate the combined effects of intentional and random mistuning on the Forced Response of bladed disks. First, the amplitude magnification due to random mistuning is reviewed. The distribution of the Response is examined for various levels of random mistuning. Next, intentional mistuning is included in the model in the absence of random mistuning. Harmonic patterns of intentional mistuning are considered, so that only a limited number of design configurations need to be examined. A heuristic technique is presented for determining the effectiveness of various intentional mistuning patterns in mitigating the damaging effects of random mistuning. It is then shown that certain intentional mistuning patterns can significantly reduce the maximum Forced Response amplitude for this rotor. Finally, the conclusions drawn from this study are summarized.

  • Forced Response of Coupled Substructures Using Experimentally Based Component Mode Synthesis
    AIAA Journal, 1997
    Co-Authors: Jeffrey A. Morgan, Christophe Pierre, Gregory M. Hulbert
    Abstract:

    A new method is presented to calculate the Forced Response of coupled substructures using experimentally based component mode synthesis (CMS). The method uses test-derived CMS matrices and the uncoupled Forced Response of each substructure to predict the coupled-system Forced Response. This is achieved by considering the internal coupling forces and external applied forces on a substructure independently, and superimposing the Responses of each. The advantage of this approach is that any number of applied forces can be present, and these can occur at unmeasurable locations. Periodic excitations are considered, and the analysis is performed in the frequency domain. The method is ideally suited for integrating test-derived models with finite element models for Forced Response predictions. A test case is conducted for a simple plate-beam system. The method is simulated analytically, then conducted experimentally using actual measured data. Good correlation is achieved for both cases.

  • Non-linear modal analysis of the Forced Response of structural systems
    1996
    Co-Authors: Nicolas Boivin, Christophe Pierre, Steven Shaw
    Abstract:

    A non-linear modal analysis procedure is presented for the Forced Response of non-linear structural systems. It utilizes the notion of invariant manifolds in the phase space, which was recently used to define non-linear normal modes and the corresponding non-linear modal analysis for unForced vibratory systems. For harmonic forcing, a similar procedure could be formulated, simply by augmenting the size of the free vibration problem. However, in order to accommodate general, non-harmonic external excitations, the invariant man-ifolds associated with the unForced system are used herein for the Forced Response analysis. The procedure allows one to generate reduced-order models for the Forced analysis of structural systems. Although strictly speaking the invariance property is violated, good results are obtained for the case study considered. In particular, it is found that fewer non-linear modes than linear modes are needed to perform a Forced modal analysis with the same accuracy. For systems with small and/or diagonal damping, approximate invariant manifolds are determined, which are shown to yield good results for both the unForced and Forced Responses.

  • Forced Response of Mistuned Bladed Disks Using Reduced-Order Modeling
    Proceedings of the 37th AIAA ASME Structures Structural Dynamics and Materials Conference, 1996
    Co-Authors: Marlin J. Kruse, Christophe Pierre
    Abstract:

    A reduced-order model formulation is presented for examining the Forced Response of tuned and mistuned\nbladed disks. The technique developed uses modal information obtained from highly detailed finite element\nmodels to create, in a systematic manner, much simpler and computationally inexpensive models of bladed\ndisks. The small size of the reduced-order model and associated computational savings enable analysts to\nexamine the effect of mistuning strength and pattern, interblade coupling, and localized modes on Forced\nResponse amplitudes. Previously, this was a formidable task with finite element modeling for even a single\nmistuning pattern.

  • Effects of Mistuning on the Forced Response of Turbomachinery Rotors
    1994
    Co-Authors: Christophe Pierre
    Abstract:

    The basic purpose of this research has been to develop a fundamental understanding of the effects of blade-to-blade dissimilarities, or mistuning, on the dynamics of nearly cyclic bladed-disk assemblies. This topic is of importance as mistuning has been shown to increase the Forced Response amplitudes of some blades significantly, and even to lead to blade failure. Furthermore, the current trend toward high performance propulsion turbomachinery designed for finite service life demands an accurate prediction of system performance and dynamics at the design stage. This objective has been achieved by carrying out the following tasks. First, the investigation of the free and Forced Responses of representative, yet sufficiently simple blade assembly models that capture all the important characteristics of typical turbomachinery rotors. Second, the development of computational methods that predict the effects of mistuning in a systematic and reliable way, along with the development of a systematic reduced-order modeling procedure for mistuned bladed disks. Third, the application of these findings and the tools developed to an industrial rotor, namely the first stage of turbine blades of the oxidizer turbopump in the space shuttle main rocket engine (SSME). The research supported by NASA has led to the development of a coherent theory for mistuned blade assemblies. The further implementation of these computational tools into the Forced Response prediction system currently under development in the Structural Dynamics Branch-FREPS-would enable the designer and the analyst to: (1) identify types of blade assemblies highly sensitive to mistuning in various frequency and other parameter ranges and (2) characterize mistuning effects on their Forced Response by predicting true Response amplitudes and fatigue life estimates.

Sanford Fleeter - One of the best experts on this subject based on the ideXlab platform.

  • Aerodynamic detuning for control of supersonic rotor Forced Response
    Computational Mechanics, 1993
    Co-Authors: K. M. Spara, Sanford Fleeter
    Abstract:

    A mathematical model is developed to analyze the aerodynamically Forced Response characteristics of a detuned rotor operating in a supersonic inlet flow field with a supersonic axial component. Alternate blade aerodynamic detuning is considered, with the aerodynamic detuning accomplished by alternating the circumferential spacing of adjacent blades. The unsteady aerodynamics are determined by developing an influence coefficient technique which is appropriate for both aerodynamically tuned and detuned rotor configurations. Rotor Forced Response is then analyzed by combining this unsteady aerodynamic model with a single-degree-of-freedom structural model. The effects of this detuning on the Forced Response characteristics of supersonic axial flow rotors is then demonstrated by applying this model to baseline twelve bladed rotors.

  • Analysis of Forced Response of detuned blade rows
    Journal de Physique III, 1992
    Co-Authors: Hsiao-wei. D. Chiang, Sanford Fleeter
    Abstract:

    A mathematical model is developed and utilized to demonstrate the enhanced Forced Response behavior associated with aerodynamic, structural, and combined aerodynamic-structural detuning of a loaded rotor operating in an incompressible flow field. The unsteady aerodynamic gust Response and oscillating cascade aerodynamics are determined by developing both a complete first-order unsteady aerodynamic analysis and a locally analytical solution in individual grid elements of a body fitted computational grid. The aerodynamic detuning is accomplished by means of alternate circumferential airfoil spacing, with alternate blade structural detuning also considered. The beneficial Forced Response effects of these detuning techniques are then demonstrated by applying this model to various detuned rotor configurations.

  • Aerodynamically Forced Response and flutter of structurally mistuned bladed disks in subsonic flow
    Journal de Physique III, 1992
    Co-Authors: Gregory Henderson, Sanford Fleeter
    Abstract:

    To analyze the aeroelastic characteristics of structurally mistuned rotors both flutter and Forced Response, a structural dynamics model appropriate for flexible bladed disks is developed utilizing flexible disk theory and small perturbation gust and motion-induced unsteady aerodynamic analyses. This model is then used to investigate the effects of structural mistuning on rotor aeroelasticity. Mistuning is found to be beneficial for flutter stability, with the motion-induced unsteady aerodynamics and thus the stability somewhat dependent on the far field acoustic wave behavior generated by the blade motion, as indicated by the acoustic resonance conditions. With regard to Forced Response, mistuning is shown to be generally detrimental.

  • Aerodynamic detuning for aeroelastic control of stability and Forced Response of supersonic rotors
    1991
    Co-Authors: K. M. Spara, Sanford Fleeter
    Abstract:

    An unsteady aerodynamic model is developed to analyze flutter and aerodynamically Forced Response of aerodynamically detuned supersonic axial flow rotors. Alternate blade aerodynamic detuning is considered, accomplished by alternating the circumferential spacing of adjacent blades as small solidity variations which do not have a dominant effect on the steady performance of a rotor. The unsteady aerodynamics are determined by developing an influence coefficient technique which is appropriate for both aerodynamically tuned and detuned rotor configurations. Torsion mode rotor stability and aerodynamically Forced Response are then analyzed with this unsteady aerodynamic model by combining it with a single-degree-of-freedom structural model. The effects of this detuning on the flutter and Forced Response characteristics of supersonic axial flow rotors is then demonstrated by considering baseline twelve bladed rotors.