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 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 Predicting the High frequency Airloads and Acoustics Associated with Blade vortex Interaction written by Mary E. Kelly and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As a rotorcraft descends or manoeuvres, the interactions which occur between the rotorblades and vortical structures within the rotor wake produce highly impulsive loads onthe blades and with these a highly intrusive external noise. Brown?s Vorticity TransportModel has been used to investigate the influence of the fidelity of the local blade aerodynamicmodel on the quality of the prediction of the high-frequency airloads associated withblade-vortex interactions and thus on the accuracy with which the acoustic signature ofthe aircraft can be predicted. Aerodynamic, wake structure and acoustic predictions usingthe Vorticity Transport Model are compared against the HART II wind tunnel data for anexperimental rotor based on the characteristics of the Bo105 rotor. The model can resolvevery accurately the structure of the wake, and allows significant flexibility in the way thatthe blade loading can be represented. The predictions of two models for the local bladeaerodynamics are compared for all three of the HART II flight cases. The first model isa simple lifting-line model and the second is a somewhat more sophisticated lifting-chordmodel based on unsteady thin aerofoil theory. The predicted positions of the vortex coresagree with measured data to within a fraction of the blade chord, and the strength ofthe vortices is preserved to well downstream of the rotor, essentially independently of theresolution of the calculation or the blade model used. A marked improvement in accuracyof the predicted high-frequency airloads and acoustic signature of the HART II rotoris obtained when the lifting-chord model for the blade aerodynamics is used instead ofthe lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Predictions of the acoustic signature of the rotor are similarly affected, with the lifting-chord model at the highest resolution producing the best representation of the distribution of sound pressure on the ground plane below therotor.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 994 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evaluation of Helicopter Noise Due to B Blade vortex Interaction for Five Tip Configurations written by and published by . This book was released on 1979 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Perpendicular Blade Vortex Interaction and Its Implications for Helicopter Noise Prediction written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-27 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt: Perpendicular blade vortex interactions are a common occurrence in helicopter rotor flows. Under certain conditions they produce a substantial proportion of the acoustic noise. However, the mechanism of noise generation is not well understood. Specifically, turbulence associated with the trailing vortices shed from the blade tips appears insufficient to account for the noise generated. The hypothesis that the first perpendicular interaction experienced by a trailing vortex alters its turbulence structure in such a way as to increase the acoustic noise generated by subsequent interactions is examined. To investigate this hypothesis a two-part investigation was carried out. In the first part, experiments were performed to examine the behavior of a streamwise vortex as it passed over and downstream of a spanwise blade in incompressible flow. Blade vortex separations between +/- one eighth chord were studied for at a chord Reynolds number of 200,000. Three-component velocity and turbulence measurements were made in the flow from 4 chord lengths upstream to 15 chordlengths downstream of the blade using miniature 4-sensor hot wire probes. These measurements show that the interaction of the vortex with the blade and its wake causes the vortex core to loose circulation and diffuse much more rapidly than it otherwise would. Core radius increases and peak tangential velocity decreases with distance downstream of the blade. True turbulence levels within the core are much larger downstream than upstream of the blade. The net result is a much larger and more intense region of turbulent flow than that presented by the original vortex and thus, by implication, a greater potential for generating acoustic noise. In the second part, the turbulence measurements described above were used to derive the necessary inputs to a Blade Wake Interaction (BWI) noise prediction scheme. This resulted in significantly improved agreement between measurements and calculations of the BWI noise spectr...

Download or read book Evaluation of Helicopter Noise Due to Blade vortex Interaction for Five Tip Configurations written by Danny R. Hoad and published by . This book was released on 1979 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Flow Structure Generated by Perpendicular Blade Vortex Interaction and Implications for Helicopter Noise Predictions written by William J. Devenport and published by . This book was released on 1994 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Cities and Their Vital Systems written by Advisory Committee on Technology and Society and published by National Academies Press. This book was released on 1989 with total page 1298 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cities and Their Vital Systems asks basic questions about the longevity, utility, and nature of urban infrastructures; analyzes how they grow, interact, and change; and asks how, when, and at what cost they should be replaced. Among the topics discussed are problems arising from increasing air travel and airport congestion; the adequacy of water supplies and waste treatment; the impact of new technologies on construction; urban real estate values; and the field of "telematics," the combination of computers and telecommunications that makes money machines and national newspapers possible.

Download or read book Journal of the American Helicopter Society written by American Helicopter Society and published by . This book was released on 2003 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book NASA Scientific and Technical Publications written by and published by . This book was released on 1991 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Study of Head on Blade Vortex Interaction Noise written by San-Yih Lin and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2004 with total page 788 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Aeronautical Engineering written by and published by . This book was released on 1971 with total page 580 pages. Available in PDF, EPUB and Kindle. Book excerpt: A selection of annotated references to unclassified reports and journal articles that were introduced into the NASA scientific and technical information system and announced in Scientific and technical aerospace reports (STAR) and International aerospace abstracts (IAA)

Download or read book Blade Vortex Interaction Noise of Rotary Wing written by Choongmo Yang and published by . This book was released on 2004 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Prediction of Blade vortex Interaction Noise Using Measured Blade Pressures written by M. C. Joshi and published by . This book was released on 1987 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ames Research Center Publications A Continuing Bibliography 1980 written by and published by . This book was released on 1981 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt: