Active flutter suppression of a two dimensional wing section in subsonic flow is studied. The equations of motion of a typical section are presented in nondimensional form. A two degree of freedom system, with pitch and plunge dynamics, combined with a trailing-edge control surface is considered. Aerodynamic loads are expressed in time-domain using Roger’s approximation. Linear optimal control is used to design a full-state feedback regulator for flutter suppression. Constraints on actuator deflection and rate limit the flutter envelope expansion. Aeroservoelastic scaling is addressed and parameters required for maintaining similarity between a full-scale system and its model are identified. Results illustrate system behavior in compressible flow. Approximate relations comparing an actively controlled flap with a continuously deforming airfoil, using piezoelectric actuation, are obtained and used to compare the performance of these two systems.
{"title":"Aeroservoelasticity in Compressible Flow and Aeroelastic Scaling Considerations","authors":"E. Presente, P. Friedmann","doi":"10.1115/imece1997-0162","DOIUrl":"https://doi.org/10.1115/imece1997-0162","url":null,"abstract":"\u0000 Active flutter suppression of a two dimensional wing section in subsonic flow is studied. The equations of motion of a typical section are presented in nondimensional form. A two degree of freedom system, with pitch and plunge dynamics, combined with a trailing-edge control surface is considered. Aerodynamic loads are expressed in time-domain using Roger’s approximation. Linear optimal control is used to design a full-state feedback regulator for flutter suppression. Constraints on actuator deflection and rate limit the flutter envelope expansion. Aeroservoelastic scaling is addressed and parameters required for maintaining similarity between a full-scale system and its model are identified. Results illustrate system behavior in compressible flow. Approximate relations comparing an actively controlled flap with a continuously deforming airfoil, using piezoelectric actuation, are obtained and used to compare the performance of these two systems.","PeriodicalId":166345,"journal":{"name":"4th International Symposium on Fluid-Structure Interactions, Aeroelasticity, Flow-Induced Vibration and Noise: Volume III","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127042581","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this article, we review the status of reduced order modeling of unsteady aerodynamic systems. Reduced order modeling is a conceptually novel and computationally efficient technique for computing unsteady flow about isolated airfoils, wings, and turbomachinery cascades. Starting with either a time domain or frequency domain computational fluid dynamics (CFD) analysis of unsteady aerodynamic or aeroacoustic flows, a large, sparse eigenvalue problem is solved using the Lanczos algorithm. Then, using just a few of the resulting eigenmodes, a Reduced Order Model of the unsteady flow is constructed. With this model, one can rapidly and accurately predict the unsteady aerodynamic response of the system over a wide range of reduced frequencies. Moreover, the eigenmode information provides important insights into the physics of unsteady flows. Finally, the method is particularly well suited for use in the active control of aeroelastic and aeroacoustic phenomena as well as in standard aeroelastic analysis for flutter or gust response. Numerical results presented include: 1) comparison of the reduced order model to classical unsteady incompressible aerodynamic theory, 2) reduced order calculations of compressible unsteady aerodynamics based on the full potential equation, 3) reduced order calculations of unsteady flow about an isolated airfoil based on the Euler equations, and 4) reduced order calculations of unsteady viscous flows associated with cascade stall flutter, 5) flutter analysis using the Reduced Order Model. The presentation will include our most recent results including the use of A-one Orthogonal Decomposition as an alternative or complement to eigenmodes.
{"title":"Reduced Order Aerodynamic Modeling of How to Make CFD Useful to an Aeroelastician","authors":"E. Dowell, K. Hall, Michael C. Romanowski","doi":"10.1115/imece1997-0166","DOIUrl":"https://doi.org/10.1115/imece1997-0166","url":null,"abstract":"\u0000 In this article, we review the status of reduced order modeling of unsteady aerodynamic systems. Reduced order modeling is a conceptually novel and computationally efficient technique for computing unsteady flow about isolated airfoils, wings, and turbomachinery cascades. Starting with either a time domain or frequency domain computational fluid dynamics (CFD) analysis of unsteady aerodynamic or aeroacoustic flows, a large, sparse eigenvalue problem is solved using the Lanczos algorithm. Then, using just a few of the resulting eigenmodes, a Reduced Order Model of the unsteady flow is constructed. With this model, one can rapidly and accurately predict the unsteady aerodynamic response of the system over a wide range of reduced frequencies. Moreover, the eigenmode information provides important insights into the physics of unsteady flows. Finally, the method is particularly well suited for use in the active control of aeroelastic and aeroacoustic phenomena as well as in standard aeroelastic analysis for flutter or gust response. Numerical results presented include: 1) comparison of the reduced order model to classical unsteady incompressible aerodynamic theory, 2) reduced order calculations of compressible unsteady aerodynamics based on the full potential equation, 3) reduced order calculations of unsteady flow about an isolated airfoil based on the Euler equations, and 4) reduced order calculations of unsteady viscous flows associated with cascade stall flutter, 5) flutter analysis using the Reduced Order Model. The presentation will include our most recent results including the use of A-one Orthogonal Decomposition as an alternative or complement to eigenmodes.","PeriodicalId":166345,"journal":{"name":"4th International Symposium on Fluid-Structure Interactions, Aeroelasticity, Flow-Induced Vibration and Noise: Volume III","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127272403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The aeroelastic equations of motion governing a hypersonic vehicle in free flight are derived. The equations of motion for a translating and rotating flexible body using Lagrange’s equations in terms of quasi-coordinates are presented. These equations are simplified for the case of a vehicle with pitch and plunge rigid body degrees of freedom and small elastic displacements. The displacements are approximated by a truncated series of the unrestrained mode shapes, which are obtained using equivalent plate theory. Subsequently, the nonlinear equations of motion are linearized about the trimmed vehicle state in horizontal flight. Unsteady aerodynamic loads for the vehicle and the appropriate stability derivatives are calculated from piston theory. The methodology for calculating the aeroelastic stability boundaries is also described. Numerical results are currently being generated.
{"title":"Aeroelastic Analysis of a Trimmed Generic Hypersonic Vehicle","authors":"I. Nydick, P. Friedmann","doi":"10.2514/6.1998-1807","DOIUrl":"https://doi.org/10.2514/6.1998-1807","url":null,"abstract":"\u0000 The aeroelastic equations of motion governing a hypersonic vehicle in free flight are derived. The equations of motion for a translating and rotating flexible body using Lagrange’s equations in terms of quasi-coordinates are presented. These equations are simplified for the case of a vehicle with pitch and plunge rigid body degrees of freedom and small elastic displacements. The displacements are approximated by a truncated series of the unrestrained mode shapes, which are obtained using equivalent plate theory. Subsequently, the nonlinear equations of motion are linearized about the trimmed vehicle state in horizontal flight. Unsteady aerodynamic loads for the vehicle and the appropriate stability derivatives are calculated from piston theory. The methodology for calculating the aeroelastic stability boundaries is also described. Numerical results are currently being generated.","PeriodicalId":166345,"journal":{"name":"4th International Symposium on Fluid-Structure Interactions, Aeroelasticity, Flow-Induced Vibration and Noise: Volume III","volume":"268 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124353001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Forces due to alternating flow states on the payload fairing of launch vehicles can couple with structural responses during transonic flight. A new methodology for the assessment of this type of self-sustained oscillation is applied for an actual launch vehicle mission. Corresponding internal launch vehicle loads are compared with those for the other transonic airloads events. The limit cycle amplitude from the analysis is compared with that from application of an existing technique in the literature. It is shown that the new methodology can be significantly less conservative than the stability criterion for bounded system responses. The historical assumption that the alternating flow forces on the payload fairing couple with a single launch vehicle bending mode is investigated through transient analysis of the fully coupled system. Evidence of alternating flow separation in flight data for the Titan IV launch vehicle is presented.
{"title":"Systems Analysis of Launch Vehicle Aeroelastic Coupling","authors":"K. W. Dotson, R. Baker, R. Bywater","doi":"10.1115/imece1997-0155","DOIUrl":"https://doi.org/10.1115/imece1997-0155","url":null,"abstract":"\u0000 Forces due to alternating flow states on the payload fairing of launch vehicles can couple with structural responses during transonic flight. A new methodology for the assessment of this type of self-sustained oscillation is applied for an actual launch vehicle mission. Corresponding internal launch vehicle loads are compared with those for the other transonic airloads events. The limit cycle amplitude from the analysis is compared with that from application of an existing technique in the literature. It is shown that the new methodology can be significantly less conservative than the stability criterion for bounded system responses. The historical assumption that the alternating flow forces on the payload fairing couple with a single launch vehicle bending mode is investigated through transient analysis of the fully coupled system. Evidence of alternating flow separation in flight data for the Titan IV launch vehicle is presented.","PeriodicalId":166345,"journal":{"name":"4th International Symposium on Fluid-Structure Interactions, Aeroelasticity, Flow-Induced Vibration and Noise: Volume III","volume":"314 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128688773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents the results of recently-completed research and presents status reports of current research being performed within the Aeroelasticity Branch of the NASA Langley Research Center. Within the paper this research is classified as experimental, analytical, and theoretical aeroelastic research. The paper also describes the Langley Transonic Dynamics Tunnel, its features, capabilities, a new open-architecture data acquisition system, ongoing facility modifications, and the subsequent calibration of the facility.
{"title":"Activities in Aeroelasticity at NASA Langley Research Center","authors":"Boyd Perry, T. Noll","doi":"10.1115/imece1997-0160","DOIUrl":"https://doi.org/10.1115/imece1997-0160","url":null,"abstract":"\u0000 This paper presents the results of recently-completed research and presents status reports of current research being performed within the Aeroelasticity Branch of the NASA Langley Research Center. Within the paper this research is classified as experimental, analytical, and theoretical aeroelastic research. The paper also describes the Langley Transonic Dynamics Tunnel, its features, capabilities, a new open-architecture data acquisition system, ongoing facility modifications, and the subsequent calibration of the facility.","PeriodicalId":166345,"journal":{"name":"4th International Symposium on Fluid-Structure Interactions, Aeroelasticity, Flow-Induced Vibration and Noise: Volume III","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128371345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A method for computational aeroelasticity in the time domain has been developed. Time-discontinuous Galerkin space-time finite elements have been employed for both the transonic fluid flow and the elastic aircraft wing structure. The resulting implicit time marching scheme is robust and higher order accurate. In order to stabilize the convective term of the fluid flow and the elastic wave propagation phenomena in the structure a Galerkin least-squares term is added. For handling discontinuities, a consistent high order nonlinear shock-capturing viscosity is applied. The aerodynamics are modeled using the compressible Euler equations. Nonlinear Timoshenko beam elements are employed for the structure. The time dependent deformation of the fluid domain is modeled using space-time mappings for the FE geometry. Based on the discretization of equal type for the fluid and the structure, an overall iterative solver strategy for the fully coupled problem is proposed. In each time step, a common loop combines the linearization of the fluid, structure and their coupling conditions. The iterative solution of the resulting linear subproblems is partly done by multigrid methods.
{"title":"Time-Discontinuous Stabilized Space-Time Finite Elements for Aeroelasticity","authors":"Boris A Grohmann, Rolf Dornberger, D. Dinkler","doi":"10.1115/imece1997-0156","DOIUrl":"https://doi.org/10.1115/imece1997-0156","url":null,"abstract":"\u0000 A method for computational aeroelasticity in the time domain has been developed. Time-discontinuous Galerkin space-time finite elements have been employed for both the transonic fluid flow and the elastic aircraft wing structure. The resulting implicit time marching scheme is robust and higher order accurate.\u0000 In order to stabilize the convective term of the fluid flow and the elastic wave propagation phenomena in the structure a Galerkin least-squares term is added. For handling discontinuities, a consistent high order nonlinear shock-capturing viscosity is applied. The aerodynamics are modeled using the compressible Euler equations. Nonlinear Timoshenko beam elements are employed for the structure. The time dependent deformation of the fluid domain is modeled using space-time mappings for the FE geometry.\u0000 Based on the discretization of equal type for the fluid and the structure, an overall iterative solver strategy for the fully coupled problem is proposed. In each time step, a common loop combines the linearization of the fluid, structure and their coupling conditions. The iterative solution of the resulting linear subproblems is partly done by multigrid methods.","PeriodicalId":166345,"journal":{"name":"4th International Symposium on Fluid-Structure Interactions, Aeroelasticity, Flow-Induced Vibration and Noise: Volume III","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125062089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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