The Experts below are selected from a list of 6609 Experts worldwide ranked by ideXlab platform
John R Hagerman - One of the best experts on this subject based on the ideXlab platform.
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SWEPTBACK UNTAPERED SEMISPAN WING OF ASPECT RATIO.1.59~UIPPED WITH VARIOUS 25-PERCENT-CHORD PLAIN FLAPS
2016Co-Authors: S. Johnsonand, John R Hagerman, S. JohnsonAbstract:A wind-tunnel investigation was made at low speed to detemine the aerodynamic characteristics of a hs ” sweptback untapered semispan wing of NACA 64.Ao1oairfoil section normal to the leading edge and aspect ratio of 1.59 equipped with 2~-percent-chordplain unsealed flaps having various spans and spanwise locations. Ltit, drag, Pitching-Moment, and flap hinge-Moment data were obtained for the wing with the various flaps-deflectedup to 600. A comparison is ~de with data obtained on the present wing at 0 ° of sweep with an aspect ratio of 3.13. In general, changes in angle of attack, flap deflection, flap span, and spanwise location produced trends in lift, drag; Pitching Moment, and flap hinge Moment that were similar to but of different magnitudes from those for unswept wings. Existing empirical and theoretical methods for predicting the lift effectiveness of flaps of various spans gave very good agreement with the experim@al results. Because of the increase in the drag coefficients and the associated decrease in the lift-drag ratio with increasing flap deflection, an advantage may be gsined by limiting the flaD deflection to moderate angles (about ~00),-even-further increases may be desirable, though the lift coefficients increase slightly with in flap deflection. Flap deflections greater than 30° however, when steeper glide-path angles are required
Jiang Lai - One of the best experts on this subject based on the ideXlab platform.
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dynamic stability of an electromagnetic suspension maglev vehicle under steady aerodynamic load
Applied Mathematical Modelling, 2021Co-Authors: Xiaohui Zeng, Dinggang Gao, Jiang LaiAbstract:Abstract In this study, the suspension stability of a maglev vehicle is investigated under steady aerodynamic load. The dynamics of the maglev vehicle in the vertical direction are modelled by considering aerodynamic lift and Pitching Moment, and this model is adopted to investigate how the aerodynamic load influences the suspension stability by analysing the critical speed by means of eigenvalue analysis and direct integration. Doing so reveals three modes of suspension failure: (i) an upward aerodynamic load or Pitching Moment can give rise to a dynamic instability, (ii) a downward aerodynamic load can give rise to a static instability and (iii) the electromagnet becomes locked in the guide-way because the vertical aerodynamic force borne by the electromagnet exceeds the vehicle weight borne by it, and the electromagnetic force cannot adjust the suspension gap. In essence, failure modes (i) and (ii) correspond to motion stability when the maglev vehicle system is perturbed by a small amount, whereas failure mode (iii) is similar to the electromagnet holding the track in the event of control failure, albeit by a different mechanism. Each suspension failure mode has its own critical speed, and how that speed depends on the aerodynamic coefficients and feedback control gains is determined.
Xiaohui Zeng - One of the best experts on this subject based on the ideXlab platform.
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dynamic stability of an electromagnetic suspension maglev vehicle under steady aerodynamic load
Applied Mathematical Modelling, 2021Co-Authors: Xiaohui Zeng, Dinggang Gao, Jiang LaiAbstract:Abstract In this study, the suspension stability of a maglev vehicle is investigated under steady aerodynamic load. The dynamics of the maglev vehicle in the vertical direction are modelled by considering aerodynamic lift and Pitching Moment, and this model is adopted to investigate how the aerodynamic load influences the suspension stability by analysing the critical speed by means of eigenvalue analysis and direct integration. Doing so reveals three modes of suspension failure: (i) an upward aerodynamic load or Pitching Moment can give rise to a dynamic instability, (ii) a downward aerodynamic load can give rise to a static instability and (iii) the electromagnet becomes locked in the guide-way because the vertical aerodynamic force borne by the electromagnet exceeds the vehicle weight borne by it, and the electromagnetic force cannot adjust the suspension gap. In essence, failure modes (i) and (ii) correspond to motion stability when the maglev vehicle system is perturbed by a small amount, whereas failure mode (iii) is similar to the electromagnet holding the track in the event of control failure, albeit by a different mechanism. Each suspension failure mode has its own critical speed, and how that speed depends on the aerodynamic coefficients and feedback control gains is determined.
Ferrari Lorenzo - One of the best experts on this subject based on the ideXlab platform.
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Aerodynamics of Darrieus Wind Turbines Airfoils: The Impact of Pitching Moment
'ASME International', 2017Co-Authors: Bianchini Alessandro, Balduzzi Francesco, Ferrara Giovanni, Ferrari LorenzoAbstract:Recent studies have demonstrated that, when rotating around an axis orthogonal to the flow direction, airfoils are virtually transformed into equivalent airfoils with a camber line defined by their arc of rotation. In these conditions, the symmetric airfoils commonly used for Darrieus blades actually behave like virtually cambered ones or, equivalently, rotors have to be manufactured with countercambered blades to ensure the attended performance. To complete these analyses, the present study first focuses the attention on the airfoils' aerodynamics during the startup of the rotors. It is shown that, contrary to conventional theories based on one-dimensional aerodynamic coefficients, symmetric airfoils exhibit a counterintuitive nonsymmetric starting torque over the revolution. Conversely, airfoils compensated for the virtual camber effect show a more symmetric distribution over the revolution. This behavior is due to the effect of the Pitching Moment, which is usually neglected in lumped parameters models. At very low revolution speeds, its contribution becomes significant due to the very high incidence angles experienced by the blades; the Pitching Moment is also nonsymmetric between the upwind and the downwind zone. For upwind azimuthal positions, the Pitching Moment reduces the overall torque output, while it changes sign in the downwind section, increasing the torque. The importance of accounting for the Pitching Moment contribution in the entire power curve is also discussed in relationship to the selection of the best blade-spoke connection (BSC) point, in order to maximize the performance and minimize the alternate stresses on the connection due to the Pitching Moment itself
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Aerodynamics of darrieus wind turbines airfoils during start-up
'ASME International', 2016Co-Authors: Bianchini Alessandro, Balduzzi Francesco, Ferrara Giovanni, Ferrari LorenzoAbstract:Recent studies have demonstrated that, when rotating around an axis orthogonal to the flow direction, airfoils are virtually transformed into equivalent airfoils with a camber line defined by their arc of rotation. In these conditions, the symmetric airfoils commonly used for Darrieus blades actually behaves like virtually cambered ones or, equivalently, rotors have to be manufactured with counter-cambered blades in order to have the performance of a symmetric airfoil. To complete these analyses, the present study focuses the attention on the airfoils' aerodynamics during the start-up of the rotors. This phase of turbines' functioning is indeed of particular interest since it actually defines the cut-in speed of the rotors and then notably impacts on the annual energy production, especially in case of small-size machines. In the work, unsteady CFD simulations have been carried out in start-up like conditions on three airfoils, i.e. a NACA 0018 and two modified profiles based on the same airfoil. The modified profiles have been conformally transformed to fit their camber lines to the arc of a circle, such that the ratio of the airfoil chord to the circle's radius is 0.114 or 0.25. The study demonstrates that all the conventional theories based on one-dimensional aerodynamic coefficients (e.g. blade element Momentum models) are affected by an intrinsic error in evaluating the starting torque profiles. Symmetric airfoils in fact exhibit a counter-intuitive non symmetric starting torque over the revolution. Conversely, airfoils compensated for the virtual camber effect show a substantially different starting torque profile, with a more symmetric distribution between the upwind and the downwind halves. This behavior is due to the effect of the Pitching Moment, which is usually neglected in lumped parameters models. At very low revolution speeds, its contribution becomes significant due to the very high angles of attack experienced by the blade. In particular, the Pitching Moment is non symmetric between the upwind and the downwind halves of the revolution. For upwind azimuthal positions the Pitching Moment reduces the overall torque output, while it changes sign in the downwind section, increasing the torque. The importance of accounting for the Pitching Moment contribution in low-order models (e.g. a blade element Momentum model) is finally discussed by comparing the predicted torque profiles with those obtained by CFD
Dinggang Gao - One of the best experts on this subject based on the ideXlab platform.
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dynamic stability of an electromagnetic suspension maglev vehicle under steady aerodynamic load
Applied Mathematical Modelling, 2021Co-Authors: Xiaohui Zeng, Dinggang Gao, Jiang LaiAbstract:Abstract In this study, the suspension stability of a maglev vehicle is investigated under steady aerodynamic load. The dynamics of the maglev vehicle in the vertical direction are modelled by considering aerodynamic lift and Pitching Moment, and this model is adopted to investigate how the aerodynamic load influences the suspension stability by analysing the critical speed by means of eigenvalue analysis and direct integration. Doing so reveals three modes of suspension failure: (i) an upward aerodynamic load or Pitching Moment can give rise to a dynamic instability, (ii) a downward aerodynamic load can give rise to a static instability and (iii) the electromagnet becomes locked in the guide-way because the vertical aerodynamic force borne by the electromagnet exceeds the vehicle weight borne by it, and the electromagnetic force cannot adjust the suspension gap. In essence, failure modes (i) and (ii) correspond to motion stability when the maglev vehicle system is perturbed by a small amount, whereas failure mode (iii) is similar to the electromagnet holding the track in the event of control failure, albeit by a different mechanism. Each suspension failure mode has its own critical speed, and how that speed depends on the aerodynamic coefficients and feedback control gains is determined.
