Download or read book Helicopter Noise Due to Blade vortex Interaction written by Sing Chu and published by . This book was released on 1971 with total page 248 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 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 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 The Effect of Tip Vortex Structure on Helicopter Noise Due to Blade vortex Interaction written by Thomas Lawrence Wolf and published by . This book was released on 1978 with total page 190 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 Helicopter Model Rotor blade Vortex Interaction Impulsive Noise Scalability and Parametric Variations written by and published by . This book was released on 1984 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: Acoustic data taken in the anechoic Deutsch-NIederlaendischer Windkanal (DNW) have documented the blade-vortex interaction (BVI) impulsive noise radiated from 1/7-scale model main rotor of the AH-1 series helicopter. Average model-scale data were compared with averaged full-scale, in-flight acoustic data under similar nondimensional test conditions. At low advance ratios (mu = 0.164-0.194), the data scale remarkably well in level and waveform shape, and also duplicate the directivity pattern of BVI impulsive noise. At moderate advance ratios (mu = 0.224-0.270), the scaling deteriorates, suggesting that the model-scale rotor is not adequately simulating the full-scale BVI noise; presently, no proved explanation of this discrepancy exists. Carefully performed parametric variations over a complete matrix of testing conditions have shown that all of the four governing nondimensional parameters -- tip Mach number at hover, advance ratio, local inflow ratio, and thrust coefficient -- are highly sensitive to BVI noise radiation. Keywords: Helicopter noise; Blade vortex interaction; Measured acoustics.

Download or read book Helicopter Impulsive Noise Theoretical and Experimental Status written by F. H. Schmitz and published by . This book was released on 1983 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: The theoretical and experimental status of helicopter impulsive noise is reviewed. The two major source mechanisms of helicopter impulsive noise are addressed: high-speed impulsive noise and blade-vortex interaction impulsive noise. A thorough physical explanation of both generating mechanisms is presented together with model and full-scale measurements of the phenomena. Current theoretical prediction methods are compared with experimental findings of isolated rotor tests. The noise generating mechanisms of high speed impulsive noise are fairly well understood - theory and experiment compare nicely over Mach number ranges typical of today's helicopters. For the case of blade-vortex interaction noise, understanding of noise generating mechanisms and theoretical comparison with experiment are less satisfactory. Several methods for improving theory-experiment are suggested.

Download or read book Correlation of Helicopter Impulsive Noise from Blade vortex Interaction with Rotor Mean Inflow written by Andrew B. Connor and published by . This book was released on 1987 with total page 28 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 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 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 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 Reduction of Blade vortex Interaction Noise Using Higher Harmonic Pitch Control written by and published by . This book was released on 1989 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in the Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4- 5 dB) were found for low-speed descent conditions, where helicopter BVI noise was most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels.

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 A Compressible High Frequency Numerical Model of Helicopter Noise Due to Blade vortex Interaction written by Luiz Hamilton de Resende Lima and published by . This book was released on 1980 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A New Experimental Approach to Study Helicopter Blade vortex Interaction Noise written by Sudarshan N. Koushik and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: