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The Effects Of Vortex Modeling On Blade Vortex Interaction Noise Prediction
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Book Synopsis The Effects of Vortex Modeling on Blade-Vortex Interaction Noise Prediction by :
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).
Author :National Aeronautics and Space Administration (NASA) Publisher :Createspace Independent Publishing Platform ISBN 13 :9781724218292 Total Pages :346 pages Book Rating :4.2/5 (182 download)
Book Synopsis Flow Structure Generated by Perpendicular Blade-Vortex Interaction and Implications for Helicopter Noise Prediction. Volume 1 by : National Aeronautics and Space Administration (NASA)
Download or read book Flow Structure Generated by Perpendicular Blade-Vortex Interaction and Implications for Helicopter Noise Prediction. Volume 1 written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-24 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: The perpendicular interaction of a streamwise vortex with an infinite span helicopter blade was modeled experimentally in incompressible flow. Three-component velocity and turbulence measurements were made using a sub-miniature four sensor hot-wire probe. Vortex core parameters (radius, peak tangential velocity, circulation, and centerline axial velocity deficit) were determined as functions of blade-vortex separation, streamwise position, blade angle of attack, vortex strength, and vortex size. The downstream development of the flow shows that the interaction of the vortex with the blade wake is the primary cause of the changes in the core parameters. The blade sheds negative vorticity into its wake as a result of the induced angle of attack generated by the passing vortex. Instability in the vortex core due to its interaction with this negative vorticity region appears to be the catalyst for the magnification of the size and intensity of the turbulent flowfield downstream of the interaction. In general, the core radius increases while peak tangential velocity decreases with the effect being greater for smaller separations. These effects are largely independent of blade angle of attack; and if these parameters are normalized on their undisturbed values, then the effects of the vortex strength appear much weaker. Two theoretical models were developed to aid in extending the results to other flow conditions. An empirical model was developed for core parameter prediction which has some rudimentary physical basis, implying usefulness beyond a simple curve fit. An inviscid flow model was also created to estimate the vorticity shed by the interaction blade, and to predict the early stages of its incorporation into the interacting vortex. Wittmer, Kenneth S. and Devenport, William J. Langley Research Center NASA-CR-200159, NAS 1.26:200159 NAG1-1539...
Book Synopsis Full-Potential Modeling of Blade-Vortex Interactions by : Henry E. Jones
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.
Book Synopsis Effect of Wake Structure on Blade-Vortex Interaction Phenomena: Acoustic Prediction and Validation by :
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).
Book Synopsis Blade-vortex Interaction Noise Generation and Directionality by : Wel-Chong Sim
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:
Book Synopsis Extraction of Blade-vortex Interactions from Helicopter Transient Maneuvering Noise by : James Harold Stephenson
Download or read book Extraction of Blade-vortex Interactions from Helicopter Transient Maneuvering Noise written by James Harold Stephenson and published by . This book was released on 2014 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt: Time-frequency analysis techniques are proposed as a necessary tool for the analysis of acoustics generated by helicopter transient maneuvering flight. Such techniques are necessary as the acoustic signals related to transient maneuvers are inherently unsteady. The wavelet transform is proposed as an appropriate tool, and it is compared to the more standard short-time Fourier transform technique through an investigation using several appropriately sized interrogation windows. It is shown that the wavelet transform provides a consistent spectral representation, regardless of employed window size. The short-time Fourier transform, however, provides spectral amplitudes that are highly dependent on the size of the interrogation window, and so is not an appropriate tool for this situation. An extraction method is also proposed to investigate blade-vortex interaction noise emitted during helicopter transient maneuvering flight. The extraction method allows for the investigation of blade-vortex interactions independent of other sound sources. The method is based on filtering the spectral data calculated through the wavelet transform technique. The filter identifies blade-vortex interactions through their high amplitude, high frequency impulsive content. The filtered wavelet coefficients are then inverse transformed to create a pressure signature solely related to blade-vortex interactions. This extraction technique, along with a prescribed wake model, is applied to experimental data extracted from three separate flight maneuvers performed by a Bell 430 helicopter. The maneuvers investigated include a steady level flight, fast- and medium-speed advancing side roll maneuvers. A sensitivity analysis is performed in order to determine the optimal tuning parameters employed by the filtering technique. For the cases studied, the optimized tuning parameters were shown to be frequencies above 7 main rotor harmonics, and amplitudes stronger than 25% (-6 dB) of the energy in the main rotor harmonic. Further, it is shown that blade-vortex interactions can be accurately extracted so long as the blade-vortex interaction peak energy signal is greater or equal to the energy in the main rotor harmonic. An in-depth investigation of the changes in the blade-vortex interaction signal during transient advancing side roll maneuvers is then conducted. It is shown that the sound pressure level related to blade-vortex interactions, shifts from the advancing side, to the retreating side of the vehicle during roll entry. This shift is predicted adequately by the prescribed wake model. However, the prescribed wake model is shown to be inadequate for the prediction of blade-vortex interaction miss distance, as it does not respond to the roll rate of the vehicle. It is further shown that the sound pressure levels are positively linked to the roll rate of the vehicle. Similar sound pressure level directivities and amplitudes can be seen when vehicle roll rates are comparable. The extraction method is shown to perform admirably throughout each maneuver. One limitation with the technique is identified, and a proposal to mitigate its effects is made. The limitation occurs when the main rotor harmonic energy drops below an arbitrary threshold. When this happens, a decreased spectral amplitude is required for filtering; which leads to the extraction of high frequency noise unrelated to blade-vortex interactions. It is shown, however, that this occurs only when there are no blade-vortex interactions present. Further, the resulting sound pressure level is identifiable as it is significantly less than the peak blade-vortex interaction sound pressure level. Thus the effects of this limitation are shown to be negligible.
Book Synopsis Prediction of Blade-vortex Interaction Noise Using Measured Blade Pressures by : M. C. Joshi
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:
Book Synopsis The Directionality of Blade-vortex Interaction Noise by : Todd Darwin Ringler
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:
Book Synopsis Helicopter Blade-Vortex Interaction Noise with Comparisons to CFD Calculations by :
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:
Author :National Aeronautics and Space Administration (NASA) Publisher :Createspace Independent Publishing Platform ISBN 13 :9781722939120 Total Pages :128 pages Book Rating :4.9/5 (391 download)
Book Synopsis An Investigation of Counterrotating Tip Vortex Interaction by : National Aeronautics and Space Administration (NASA)
Download or read book An Investigation of Counterrotating Tip Vortex Interaction written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: A tip vortex interaction model originally developed for compressors has been extended and adapted for use with counterrotating open rotors. Comparison of available acoustic data with predictions (made with and without the tip vortex model included) illustrate the importance of this interaction effect. This report documents the analytical modeling, a limited experimental verification, and certain key parametric studies pertaining to the tip vortex as a noise source mechanism for the unsteady loading noise of counterrotating properllers. Majjigi, R. K. and Uenishi, K. and Gliebe, P. R. Unspecified Center AEROACOUSTICS; BLADE-VORTEX INTERACTION; COUNTER ROTATION; PROPELLER NOISE; ROTOR AERODYNAMICS; UNSTEADY AERODYNAMICS; VORTICES; APPLICATIONS PROGRAMS (COMPUTERS); BLADE TIPS; FLOW DISTRIBUTION; GUST LOADS; MATHEMATICAL MODELS; UPWASH; WAKES...
Book Synopsis Discrete Vortex Modeling of a Blade-vortex Interaction by : Piergiovanni Renzoni
Download or read book Discrete Vortex Modeling of a Blade-vortex Interaction written by Piergiovanni Renzoni and published by . This book was released on 1987 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Wake Geometry Effects on Rotor Blade-vortex Interaction Noise Directivity by : Ruth McVoy Martin
Download or read book Wake Geometry Effects on Rotor Blade-vortex Interaction Noise Directivity written by Ruth McVoy Martin and published by . This book was released on 1990 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Computational Investigation of Blade Vortex Interaction Noise by : See-Ho Wong
Download or read book Computational Investigation of Blade Vortex Interaction Noise written by See-Ho Wong and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Design and Preliminary Tests of a Blade Tip Air Mass Injection System for Vortex Modification and Possible Noise Reduction on a Full-scale Helicopter Rotor by :
Download or read book Design and Preliminary Tests of a Blade Tip Air Mass Injection System for Vortex Modification and Possible Noise Reduction on a Full-scale Helicopter Rotor written by and published by . This book was released on 1975 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis NASA Technical Paper by : United States. National Aeronautics and Space Administration
Download or read book NASA Technical Paper written by United States. National Aeronautics and Space Administration and published by . This book was released on 1990 with total page 656 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Computational Study of High Speed Blade-vortex Interaction by : Erkan Yildirim
Download or read book Computational Study of High Speed Blade-vortex Interaction written by Erkan Yildirim and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book NASA Technical Paper written by and published by . This book was released on 1990 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt:
