Download or read book Aerodynamic Aspects of Blade vortex Interaction BVI written by Chee Tung and published by . This book was released on 1996 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Full Potential Modeling of Blade Vortex Interactions written by Henry E. Jones and published by . This book was released on 1997 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Aerodynamic Requirements for Bvi Noise Control written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-30 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: As a rotor blade moves through the air, it sheds vortices. These vortices shed along the length of the blade over time form the wake. The strongest vortices of the wake are those trailing from the tip of the blade. When a rotating blade system moves under certain operating conditions, each blade will impinge on the tip vortices shed by itself or other blades. This impingement is called a blade-vortex interaction, or BVI. Although the blade and trailing tip vortices interact with many different orientations, one of the two extremes, either parallel or perpendicular interaction, is usually modelled. In a perpendicular interaction, the portion of the blade that is actually interacting with the travelling vortex at any given time is very small. A parallel interaction, however, has the largest concurrent interaction with the blade, as a result this case is given the most attention. One of the most commonly studied occurrences of blade-vortex interactions is associated with low-speed descending rotorcraft flight. BVI occur when the tip vortices shed by the blades intersect the plane of the rotor. BVI cause local pressure changes over the blades which are responsible, in part, for the acoustic signature of the rotorcraft. The local pressure changes also cause vibrations which lead to fatigue of both the blades and the mechanical components driving the blades. Wells, Valana L. Ames Research Center NAG2-844...

Download or read book Reduction of Blade Vortex Interaction BVI Noise Through X force Control written by Fredric H. Schmitz and published by . This book was released on 1995 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Blade vortex Interaction Noise Generation and Directionality written by Wel-Chong Sim and published by . This book was released on 1996 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Wake Structure on Blade Vortex Interaction Phenomena Acoustic Prediction and Validation written by and published by . This book was released on 1995 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the Higher Harmonic Control Aeroacoustic Rotor Test, extensive measurements of the rotor aerodynamics, the far-field acoustics, the wake geometry and the blade motion for powered, descent, flight conditions were made. These measurements have been used to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the evaluation of the test data are discussed. The effects of these improvements on the acoustic-pressure predictions are shown. These improvements include re-structuring the wake, modifying the core size, incorporating the measured blade motion into the calculations and attempting to improve the dynamic blade response. A comparison of four different implementations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison. (AN).

Download or read book Advancing Side Directivity and Retreating Side Interactions of Model Rotor Blade Vortex Interaction Noise written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-30 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: Acoustic data are presented from a 40 percent scale model of the four-bladed BO-105 helicopter main rotor, tested in a large aerodynamic wind tunnel. Rotor blade-vortex interaction (BVI) noise data in the low-speed flight range were acquired using a traversing in-flow microphone array. Acoustic results presented are used to assess the acoustic far field of BVI noise, to map the directivity and temporal characteristics of BVI impulsive noise, and to show the existence of retreating-side BVI signals. The characterics of the acoustic radiation patterns, which can often be strongly focused, are found to be very dependent on rotor operating condition. The acoustic signals exhibit multiple blade-vortex interactions per blade with broad impulsive content at lower speeds, while at higher speeds, they exhibit fewer interactions per blade, with much sharper, higher amplitude acoustic signals. Moderate-amplitude BVI acoustic signals measured under the aft retreating quadrant of the rotor are shown to originate from the retreating side of the rotor. Martin, R. M. and Splettstoesser, W. R. and Elliott, J. W. and Schultz, K.-J. Langley Research Center RTOP 505-61-51-06...

Download or read book A Parametric Study of Transonic Blade Vortex Interaction Noise written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-02 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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...

Download or read book Transonic Effects on Aerodynamics and Acoustics of Blade vortex Interaction written by Rajneesh K. Singh and published by . This book was released on 1999 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Helicopter Blade Vortex Interaction Noise with Comparisons to Cfd Calculations written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-08 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comparison of experimental acoustics data and computational predictions was performed for a helicopter rotor blade interacting with a parallel vortex. The experiment was designed to examine the aerodynamics and acoustics of parallel Blade-Vortex Interaction (BVI) and was performed in the Ames Research Center (ARC) 80- by 120-Foot Subsonic Wind Tunnel. An independently generated vortex interacted with a small-scale, nonlifting helicopter rotor at the 180 deg azimuth angle to create the interaction in a controlled environment. Computational Fluid Dynamics (CFD) was used to calculate near-field pressure time histories. The CFD code, called Transonic Unsteady Rotor Navier-Stokes (TURNS), was used to make comparisons with the acoustic pressure measurement at two microphone locations and several test conditions. The test conditions examined included hover tip Mach numbers of 0.6 and 0.7, advance ratio of 0.2, positive and negative vortex rotation, and the vortex passing above and below the rotor blade by 0.25 rotor chords. The results show that the CFD qualitatively predicts the acoustic characteristics very well, but quantitatively overpredicts the peak-to-peak sound pressure level by 15 percent in most cases. There also exists a discrepancy in the phasing (about 4 deg) of the BVI event in some cases. Additional calculations were performed to examine the effects of vortex strength, thickness, time accuracy, and directionality. This study validates the TURNS code for prediction of near-field acoustic pressures of controlled parallel BVI. McCluer, Megan S. Ames Research Center...

Download or read book Aerodynamics of Two Dimensional Blade Vortex Interaction written by G. R. Srinivasan and published by . This book was released on 1985 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Helicopter Blade vortex Interaction Locations written by Danny R. Hoad and published by . This book was released on 1987 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Helicopter Blade Vortex Interaction Noise with Comparisons to CFD Calculations written by and published by . This book was released on 1996 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rotorcraft Blade vortex Interaction Noise Reduction Through Attitude and Flight Parameter Variations written by Juan Abelló and published by . This book was released on 2004 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Directionality of Blade vortex Interaction Noise written by Todd Darwin Ringler and published by . This book was released on 1992 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Simulation of Transonic Vortex Airfoil Interactions written by Donald R. Wilson and published by . This book was released on 1988 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results from an experimental investigation of helicopter rotor blade-vortex interaction (BVI) phenomena at transonic Mach numbers and at Reynolds numbers representative of actual helicopter flight operations are presented. The study examined both perpendicular (vortex core perpendicular to the blade leading edge) and parallel (vortex core parallel to blade leading edge) interaction geometries. The significant results are: 1. Perpendicular Interaction: The effect of the vortex causes a large reduction in upper surface pressure distribution (lift increase). This lift increase correlates with strength of the vortex and closeness of the vortex encounter. The interaction is most pronounced near the leading edge of the airfoil. A large spanwise deflection of the vortex is observed as it passes over the airfoil. 2. Parallel Interaction: A similar reduction in upper surface pressure distribution is also observed during the transient passage of the parallel vortex over the airfoil. Like the perpendicular interaction, this effect is also most pronounced near the leading edge, which is in contrast to the general results of numerous CFD simulations. For certain combinations of vortex strength and encounter distance, a class-C shock motion (forward propagation of the airfoil shock wave) was observed. Keywords: Blade vortex interaction; Transonic aerodynamics. (jhd).

Download or read book Investigation of the Orthogonal Blade Vortex Interaction written by and published by . This book was released on 2003 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Stereoscopic Particle Image Velocimetry (SPIV) system was developed and applied to measurements of the Orthogonal Blade-Vortex Interaction (BVI) in a wind tunnel. Measurements of the isolated vortex showed that the SPIV system could resolve the jet velocity profile within the vortex core to a reasonable accuracy, and views of the vortex from different sides of the wind tunnel showed similar velocity profiles. For the BVI measurements the SPIV system showed the existence of a strong.