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 Helicopter Blade vortex Interaction Noise with Comparisons to CFD Calculations written by Megan S. McCluer and published by . This book was released on 1996 with total page 51 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 New Computational Methods for the Prediction and Analysis of Helicopter Noise written by Roger C. Strawn and published by . This book was released on 1996 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: "This paper describes several new methods to predict and analyze rotorcraft noise. These methods are: 1) a combined computational fluid dynamics and Kirchhoff scheme for far-field noise predictions, 2) parallel computer implementation of the Kirchhoff integrations, 3) audio and visual rendering of the computed acoustic predictions over large far-field regions, and 4) acoustic tracebacks to the Kirchhoff surface to pinpoint the sources of the rotor noise. The paper describes each method and presents sample results for three test cases. The first case consists of in-plane high-speed impulsive noise and the other two cases show idealized parallel and oblique blade-vortex interactions. The computed results show good agreement with available experimental data but convey much more information about the far-field noise propagation. When taken together, these new analysis methods exploit the power of new computer technologies and offer the potential to significantly improve our prediction and understanding of rotorcraft noise."
Download or read book Helicopter Noise Part 1 Review and theoretical study written by John W. Leverton and published by . This book was released on 1968 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Overset Grid Navier Stokes Kirchhoff surface Method for Rotorcraft Aeroacoustic Predictions written by Earl P. N. Duque and published by . This book was released on 1996 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: "This paper describes a new method for computing the flowfield and acoustic signature of arbitrary rotors in forward flight. The overall scheme uses a finite-difference Navier-Stokes solver to compute the aerodynamic flowfield near the rotor blades. The equations are solved on a system of overset grids that allow for prescribed cyclic and flapping blade motions and capture the interactions between the rotor blades and wake. The far-field noise is computed with a Kirchhoff integration over a surface that completely encloses the rotor blades. Flowfield data are interpolated onto this Kirchhoff surface using the same overset-grid techniques that are used for the flowfield solution. As a demonstration of the overall prediction scheme, computed results for far-field noise are compared with experimental data for both high-speed impulsive (HSI) and blade-vortex interaction (BVI) cases. The HSI case showed good agreement with experimental data while a preliminary attempt at the BVI case did not. The computations clearly show that temporal accuracy, spatial accuracy and grid resolution in the Navier-Stokes solver play key roles in the overall accuracy of the predicted noise. These findings will be addressed more closely in future BVI computations. Overall, the overset-grid CFD scheme provides a powerful new framework for the prediction of helicopter noise."
Download or read book The Investigation of Blade vortex Interaction Noise Using Computational Fluid Dynamics written by Romuald Morvant and published by . This book was released on 2004 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Rotating Hot wire Investigation of the Vortex Responsible for Blade vortex Interaction Noise written by and published by . This book was released on 1988 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Helicopter Noise Due to Blade Vortex Interaction written by Hussein Hasan Nijim and published by . This book was released on 1973 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Free Wake Euler and Navier Stokes CFD Method and Its Application to Helicopter Rotors Including Dynamic Stall written by and published by . This book was released on 1993 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report summarizes the results of the research in two parts. Part I describes the development and application of a free-wake Euler and Navier- Stokes computational fluid dynamics method, called 'TURNS', for helicopter applications. This finite-difference, implicit, upwind numerical method uses structured grids, and has been used for calculating the viscous, three- dimensional flow-fields of rotors in hover, forward flight, blade-vortex interactions, and high speed impulsive noise. The good agreement of numerical results with experiments for surface pressures, wake trajectory, thrust, power, Figure of Merit, and acoustic wave forms indicate the accuracy and suitability of the numerical method. It is demonstrated that both aerodynamics and acoustics information can be obtained in a single solution of the governing equations. In Part II, the unsteady flowfield results of a two-dimensional oscillating wing are presented for five widely used turbulence models and compared with experiments. The accuracy and suitability of turbulence models for unsteady separated flow axe discussed. Free-wake, Hover, Viscous, Three-dimensional, Forward flight, Helicopter, Dynamic stall, Light-stall, Deep-stall, Unsteady, Euler, Navier-stokes, Blade-vortex interaction, Impulsive noise.
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 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.
Download or read book Quasi static Acoustic Mapping of Helicopter Blade vortex Interaction Noise written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Blade Vortex Interaction Noise Characteristics of a Utility Helicopter at 1 4 Scale written by and published by . This book was released on 1984 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Signal Analysis of Helicopter Blade Vortex Interaction Acoustic Noise written by Renshou Dai and published by . This book was released on 1997 with total page 134 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:
