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 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 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 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 Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA SP written by and published by . This book was released on 1993 with total page 360 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 The Effects of Vortex Modeling on Blade Vortex Interaction Noise Prediction written by and published by . This book was released on 1995 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of a blade vortex interaction noise prediction scheme, based on CAMRAD/JA, FPR and RAPP, quantifies the effects of errors and assumptions in the modeling of the helicopter's shed vortex on the acoustic predictions. CAMRAD/JA computes the wake geometry and inflow angles that are used in FPR to solve for the aerodynamic surface pressures. RAPP uses these surface pressures to predict the acoustic pressure. Both CAMRAD/JA and FPR utilize the Biot-Savart Law to determine the influence of the vortical velocities on the blade loading and both codes use an algebraic vortex model for the solid body rotation of the vortex core. Large changes in the specification of the vortex core size do not change the inplane wake geometry calculated by CAMRAD/JA and only slighty affect the out-of-plane wake geometry. However, the aerodynamic surface pressure calculated by FPR changes in both magnitude and character with small changes to the core size used by the FPR calculations. This in turn affects the acoustic predictions. Shifting the CAMRAD/JA wake geometry away from the rotor plane by 1/4 chord produces drastic changes in the acoustic predictions indicating that the prediction of acoustic pressure is extremely sensitive to the miss distance between the vortex and the blade and that this distance must be calulated as accurately as possible for acceptable noise predictions. The inclusion or exclusion of a vortex in the FPR-RAPP calculation allows for the determination of the relative importance of that vortex as a BVI noise source. (AN).
Download or read book Aeroacoustics of Flight Vehicles written by Harvey H. Hubbard and published by . This book was released on 1991 with total page 620 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1996 with total page 948 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 NASA Reference Publication written by and published by . This book was released on 1977 with total page 628 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 The Aeronautical Journal written by and published by . This book was released on 1992 with total page 474 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Journal of Aircraft written by and published by . This book was released on 1997 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Verti flite written by and published by . This book was released on 1998 with total page 592 pages. Available in PDF, EPUB and Kindle. Book excerpt:
