Two- and Three-dimensional Blade Vortex Interactions PDF Download
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Languages : en
Pages : 226
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Author:
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ISBN:
Category :
Languages : en
Pages : 226
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Author: G. R. Srinivasan
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Category :
Languages : en
Pages : 20
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Book Description
A computational procedure and some numerical results of unsteady interaction of a helicopter rotor blade with a Lamb-like vortex of finite viscous core in subsonic and transonic flows is presented. The interaction considered here is one of the limiting cases of a more complex interaction typically encountered on helicopter rotor blade. In this limit, the interacting flow field is considered to be unsteady but two-dimensional. Accordingly, unsteady, two-dimensional, thin-layer Navier-Stokes equations are solved using a prescribed-vortex method (also called perturbation method) for the cases of stationary and moving rotor blades encountering a moving vortex passing the blades. The numerical results are compared with the recent experimental data of Caradonna et al. for the latter case. The comparison shows that for the transonic cases, the flow field is dominated by the presence of the shock waves, with strong indications of unsteady time lags in the shock-wave motions and shock-wave strengths, and of important three-dimensional effects. For subcritical-flow cases, however, the unsteady lag effects on the basic rotor blade are absent, and three-dimensional effects appear to be negligible, unlike the supercritical case. The subcritical calculations are in good agreement with the experimental data.
Author: F. N. Coton
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ISBN:
Category :
Languages : en
Pages : 19
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Author: Henry E. Jones
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Category : Unsteady flow (Aerodynamics)
Languages : en
Pages : 96
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A study of the full-potential modeling of a blade-vortex interaction was made. A primary goal of this study was to investigate the effectiveness of the various methods of modeling the vortex. The model problem restricts the interaction to that of an infinite wing with an infinite line vortex moving parallel to its leading edge. This problem provides a convenient testing ground for the various methods of modeling the vortex while retaining the essential physics of the full three-dimensional interaction. A full-potential algorithm specifically tailored to solve the blade-vortex interaction (BVI) was developed to solve this problem. The basic algorithm was modified to include the effect of a vortex passing near the airfoil. Four different methods of modeling the vortex were used: (1) the angle-of-attack methods, (2) the lifting-surface method, (3) the branch-cut method, and (4) the split-potential method. A side-by-side comparison of the four models was conducted. these comparisons included comparing generated velocity fields, a subcritical interaction, and a critical interaction. The subcritical and critical interactions are compared with experimentally generate results. The split-potential model was used to make a survey of some of the more critical parameters which affect the BVI.
Author:
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Category :
Languages : en
Pages : 32
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Author: Earl R. Booth
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Category :
Languages : en
Pages : 0
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Author: Anastasios Sotirios Lyrintzis
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Category : Aerodynamics, Transonic
Languages : en
Pages : 306
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Author: Erkan Yildirim
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Category :
Languages : en
Pages :
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This thesis presents inviscid compressible simulations for the orthogonal blade-vortex interaction. A numerical model between the tail rotor of a helicopter and the trailing vortex system formed by the main rotor blades is assumed. The study takes a 'building-block' approach to investigating this problem. Firstly, the impulsive instantaneous blocking of the axial core flow by a flat plate is considered. In the second step, the three-dimensional gradual cutting of the vortex by a sharp flat-plate that moves at a finite speed through the vortex is performed. Finally the chopping of the vortex by a blunt leading edge aerofoil, which incorporates both the blocking effect and also the stretching and distortion of the vortex lines is studied. The solutions reveal that the compressibility effects are strong when the axial core flow of the vortex is impulsively blocked. This generates a weak shock-expansion structure propagating along the vortex core on opposite sides of the cutting surface. The shock and expansion waves are identified as the prominent acoustic signatures in the interaction. In a simplified, two-dimensional axisymmetric model, the modelling of the physical evolution of the vortex, including the evolution of the complex vortical structures that controls the vortex core size near the cutting surface, are studied. Furthermore, the three dimensional simulations revealed that there is a secondary and a tertiary noise sources due to compressibility effects at the blade leading edge and due to the shock-vortex interaction taking place on the blade, which is exposed to a transonic free-stream flow.
Author:
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ISBN:
Category :
Languages : en
Pages : 44
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Author: Ganapathi R. Srinivasan
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Category :
Languages : en
Pages : 68
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Book Description
This report presents viscous, three-dimensional numerical solutions of two related problems of a helicopter rotor. An implicit, finite-difference numerical procedure is used for the solution of the thin layer Navier-Stokes equations to simulate the flowfield solutions of (1) helicopter rotor blade encountering a passing concentrated line vortex, and (2) a lifting hovering rotor, at both sub- and super-critical flowfield conditions. For the first problem, the Euler equations were also solved independently to assess the importance of the viscous effects in the interacting flowfield. A prescribed vortex method is adopted to preserve the structure of the interacting vortex. Both parallel and oblique blade-vortex interactions have been calculated. The second problem considered is that of calculating lifting hovering rotor flowfields without using any ad hoc wake models. The induced effects of the wake, including the interaction of tip vortices with successive blades, are captured as a part of the overall flowfield solution and hence no wake models are used. In order to preserve the structure of the vortex wake, a completely upwind finite-difference numerical procedure is used for this problem. Comparison of the numerical results show excellent agreement with the experimental data and with the previously published Navier-Stokes calculations that used a simple wake model. (jhd).
