The Experts below are selected from a list of 51 Experts worldwide ranked by ideXlab platform
John H G Macdonald - One of the best experts on this subject based on the ideXlab platform.
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An analytical solution for the galloping stability of a 3 degree-of-freedom system based on quasi-steady theory
Journal of Fluids and Structures, 2016Co-Authors: Mingzhe He, John H G MacdonaldAbstract:The Aerodynamic forces on a two-dimensional three-degree-of-freedom (3DOF-heave, sway and torsion) body of arbitrary cross-section are considered, for arbitrary wind direction relative to the principal structural axes. The full 3DOF Aerodynamic damping matrix is derived, based on quasi-steady theory, using the commonly-used concept of an Aerodynamic Centre to represent the effect of the torsional velocity on the Aerodynamic forces. The Aerodynamic coefficients are assumed to be consistent functions of only the relative angle of attack. It is shown that the determinant of the quasi-steady Aerodynamic damping matrix is always zero. The galloping stability of the Aerodynamically coupled system is then addressed by formulating the eigenvalue problem, for which analytical solutions are derived for the case of perfectly tuned structural natural frequencies. The solutions define a non-dimensional effective Aerodynamic damping coefficient, indicating how stable the system is. A trivial solution always exists, with zero effective Aerodynamic damping, corresponding to rotation about the Aerodynamic Centre, and relatively simple exact closed-form solutions are derived for the other one or two solutions, the minimum solution defining the stability of the system. Example results are presented and discussed for square, rectangular (aspect ratio 3) and equilateral triangular sections and a lightly iced cable, and they are compared with results using previous solutions for 2DOF translational and 1DOF pure torsional galloping. For the shapes considered it is found that the stability of the 3DOF system is normally close to that of the 2DOF translational system, with a relatively small influence of the stability of the torsional degree of freedom, although in some instances, especially at the critical angles of attack, it can significantly affect the stability.
Mingzhe He - One of the best experts on this subject based on the ideXlab platform.
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An analytical solution for the galloping stability of a 3 degree-of-freedom system based on quasi-steady theory
Journal of Fluids and Structures, 2016Co-Authors: Mingzhe He, John H G MacdonaldAbstract:The Aerodynamic forces on a two-dimensional three-degree-of-freedom (3DOF-heave, sway and torsion) body of arbitrary cross-section are considered, for arbitrary wind direction relative to the principal structural axes. The full 3DOF Aerodynamic damping matrix is derived, based on quasi-steady theory, using the commonly-used concept of an Aerodynamic Centre to represent the effect of the torsional velocity on the Aerodynamic forces. The Aerodynamic coefficients are assumed to be consistent functions of only the relative angle of attack. It is shown that the determinant of the quasi-steady Aerodynamic damping matrix is always zero. The galloping stability of the Aerodynamically coupled system is then addressed by formulating the eigenvalue problem, for which analytical solutions are derived for the case of perfectly tuned structural natural frequencies. The solutions define a non-dimensional effective Aerodynamic damping coefficient, indicating how stable the system is. A trivial solution always exists, with zero effective Aerodynamic damping, corresponding to rotation about the Aerodynamic Centre, and relatively simple exact closed-form solutions are derived for the other one or two solutions, the minimum solution defining the stability of the system. Example results are presented and discussed for square, rectangular (aspect ratio 3) and equilateral triangular sections and a lightly iced cable, and they are compared with results using previous solutions for 2DOF translational and 1DOF pure torsional galloping. For the shapes considered it is found that the stability of the 3DOF system is normally close to that of the 2DOF translational system, with a relatively small influence of the stability of the torsional degree of freedom, although in some instances, especially at the critical angles of attack, it can significantly affect the stability.
Yoshiaki Kodama - One of the best experts on this subject based on the ideXlab platform.
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FLOW COMPUTATION FOR THREE-DIMENSIONAL WING IN GROUND EFFECT USING MULTI-BLOCK TECHNIQUE
Journal of the Society of Naval Architects of Japan, 2010Co-Authors: Nobuyuki Hirata, Yoshiaki KodamaAbstract:A WIG (Wing In Ground effect) vehicle is expected to be one of the promising super-high speed craft in the next generation. A WIG is characterized by a high lift to drag ratio and a backward shift of Aerodynamic Centre in close proximity to the ground, hence estimating their features accurately is very important in design and safety evaluation. In the present investigation, flows around a three-dimensional wing with end-plates in ground effect are computed by a Navier-Stokes solver. Because of the geometric complexity of the configuration, a multi-block technique is used. In order to clarify the Aerodynamic interaction between the wing and the ground, two boundary conditions on the ground are considered, that is case 1) velocity is equal to the uniform flow and case 2) no slip condition. They correspond to an actual operating condition and a wind-tunnel condition with a ground plate respectively. The flows with different ground heights are computed by the solver. Results are compared with experimental data and the Aerodynamic characteristics in ground effect are discussed.
A. T. Sayers - One of the best experts on this subject based on the ideXlab platform.
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Experimental Investigation: Stability Criteria of an Uncambered Airfoil in Ground Effect
2020Co-Authors: S. C. Rhodes, A. T. SayersAbstract:× × for relative ground clearances of 0.06 < h 0 < 1.8, and angles of attack between ‐9 and 37°. Data is presented for lift, drag, pitching moment, Aerodynamic Centre in pitch (ACP), Aerodynamic Centre in height (ACH) and static stability margin (SSM) versus angle of attack and ground clearance. The data shows that at relative ground clearances h0 < 0.5, the wing experiences a rapid deterioration of the SSM for typical flight cruise angles. This eff ect is attributed to a loss in lift as the ground is approached. The ACH was found to be predominantly behind the ACP. The SSM was, thus, predominantly negative at all ground clearances, implying that the wing was unstable in ground effect.
Faisal Azeem - One of the best experts on this subject based on the ideXlab platform.
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determination of Aerodynamic Centre location and stalling characteristics of a new cusped leading edge airfoil
Global Sci-Tech, 2015Co-Authors: Shujaut Hussain Bader, Sharique Akhtar, Faisal AzeemAbstract:Various designs of airfoils have been proposed to reduce the drag considerably in the supersonic flow regime by the mitigation of shock waves. In this paper we have analyzed one such design with cusped leading edge. The numerical investigation involves modelling the flow as two-dimensional unsteady, viscous and laminar compressible flow around a new design of cusped leading edge airfoil. The specific aerofoil geometry with a maximum thickness of 10-percent of chord located at 75percent of the chord is considered. The main. focus of the present work is to find out the effects of variation of Mach number in supersonic regime, and angle of attack at a constant value of Reynolds number on the location of Aerodynamic Centre and stalling characteristics. The constant value of Reynolds number is taken as 5x105 and the Mach numbers considered are 1.25, 1.85 and 2.13. Different angles of attack given as α=4°, 8°, 12°, 16°, 24° and 30° are considered for the study. The stalling characteristics as derived from lift to drag ratio have been found to occur at around α = 4° at M= 1.25, α = 6° at M=1.85 and α =6° at M = 2.13 which is in accordance with the designs of NACA supersonic airfoils. Furthermore, the Aerodynamic Centre lies on the chord with varying coordinates along the chord with respect to angle of attack. For such values of angle of attack where the characteristics of CN vs α are linear, the Aerodynamic Centre is nearly independent of the angle of attack. Comparison of the stalling characteristics and the Aerodynamic Centre coordinates with the existing NACA supersonic airfoils validates our data.
