A Numerical Study of the Transonic Blade-vortex Interaction PDF Download
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Author: Nguk Lan Ng
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Languages : en
Pages :
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Author: Nguk Lan Ng
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Languages : en
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Author: San-Yih Lin
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Languages : en
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722140960
Category :
Languages : en
Pages : 60
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Several parameters of transonic blade-vortex interactions (BVI) are being studied and some ideas for noise reduction are introduced and tested using numerical simulation. The model used is the two-dimensional high frequency transonic small disturbance equation with regions of distributed vorticity (VTRAN2 code). The far-field noise signals are obtained by using the Kirchhoff method with extends the numerical 2-D near-field aerodynamic results to the linear acoustic 3-D far-field. The BVI noise mechanisms are explained and the effects of vortex type and strength, and angle of attack are studied. Particularly, airfoil shape modifications which lead to noise reduction are investigated. The results presented are expected to be helpful for better understanding of the nature of the BVI noise and better blade design. Lyrintzis, A. S. Unspecified Center...
Author: N. Ng
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Category :
Languages : en
Pages :
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Author: A. R. George
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Category :
Languages : en
Pages : 49
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Blade-vortex interaction noise from full-scale helicopters is shown to involve unsteady transonic flow phenomena which can be modeled as two-dimensional. An unsteady, small-disturbance-theory, numerical analysis, is used to model the interaction of an airfoil with a finite-core, locally-convected vortex using the vortex-in-cell method with multiple branch cuts accounting for the distributed vortices' potential jumps. Strong disturbances propagating from the blade-vortex interaction are associated with occurrence of Tijdeman's Type C flow on the airfoil's lower surface. In this type of flow, the shock which initially terminates a supersonic zone propagates through it and forward off the airfoil. The effects of airfoil shape, angle of attack, Mach number, vortex strength, and vortex miss distance on the flow and on waves radiated forward are investigated. It is found that stronger radiated waves are associated with narrow supersonic regions and near-sonic base flow. Also, stronger vortices generate stronger radiated waves, but miss distance is not as important a factor. Originator-supplied keywords include: Acoustics, Noise(Sound), and Numerical analysis.
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 : Mechanics, Applied
Languages : en
Pages : 556
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Author: Erkan Yildirim
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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: Amer Hussain Sheikh
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Category :
Languages : en
Pages :
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Author: Amer Hussain Sheikh
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Category :
Languages : en
Pages :
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