Download or read book The Acoustic Shielding of Noise by a Jet Wing written by Frederick Mark Sears and published by . This book was released on 1975 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Prediction of Jet Noise Shielding with Forward Flight Effects written by Salvador Mayoral and published by . This book was released on 2013 with total page 181 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aircraft noise continues to be a major concern among airport-neighboring communities. A strong component of aircraft noise is the jet noise that is generated from the turbulent mixing between the jet exhaust and ambient medium. The hybrid wing body aircraft suppresses jet noise by mounting the engines over-the-wing so that the airframe may shield ground observers from jet noise sources. Subscale jet noise shielding measurements of a scaled-down turbofan nozzle and a model of the hybrid wing body planform are taken with two 12-microphone polar arrays. Chevrons and wedge-type fan flow deflectors are integrated into the baseline bypass ratio 10 (BPR10) nozzle to modify the mean flow and alter the noise source behavior. Acoustic results indicate that the baseline BPR10 nozzle produces a long noise source region that the airframe has difficulty shielding, even when the nozzle is translated two fan diameters upstream of its nominal position. The integration of either chevrons or fan flow deflectors into the nozzle is essential for jet noise shielding because they translate peak intensities upstream, closer to the fan exit plane. The numerical counterpart of this study transforms the system of equations governing the acoustic diffraction with forward flight into the wave equation. Two forward flight formulations are considered: uniform flow over slender body; and non-uniform potential flow at low Mach number. The wave equation is solved numerically in the frequency domain using the boundary element method. The equivalent jet noise source is modeled using the combination of a wavepacket and a monopole. The wavepacket is parameterized using the experimental far-field acoustic autospectra of the BPR10 jets and knowledge of their peak noise locations. It is shown that the noise source compacts with increasing Mach number and consequently there is an increase in shielding. An assessment of the error associated with the non-uniform formulation for forward flight shows that the error is low for Mach numbers less than or equal to 0.2, but can be on the same scale as the acoustic scatter field when the Mach number is 0.6.
Download or read book Database of Inlet and Exhaust Noise Shielding for Wedge shaped Airframe written by Carl H. Gerhold and published by . This book was released on 2001 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experiment to measure the noise shielding of the blended wing body design concept was developed using a simplified wedge-shaped airframe. The experimental study was conducted in the Langley Anechoic Noise Research facility. A wideband, omnidirective sound source in a simulated engine nacelle was held at locations representative of a range of engine locations above the wing. The sound field around the model was measured, with the airframe and source in place and with source alone, using an array of microphones on a rotating hoop that is also translated along an axis parallel to the airframe axis. The insertion loss was determined from the difference between the two resulting contours. Although no attempt was made to simulate the noise characteristics of a particular engine, the broadband noise source radiated sound over a range of scaled frequencies encompassing 1 and 2 times the blade passage frequency representative of a large, high-bypass-ratio turbofan engine.
Download or read book Aircraft Noise written by Oleksandr Zaporozhets and published by CRC Press. This book was released on 2011-05-13 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aircraft noise has adverse impacts on passengers, airport staff and people living near airports, it thus limits the capacity of regional and international airports throughout the world. Reducing perceived noise of aircraft involves reduction of noise at source, along the propagation path and at the receiver. Effective noise control demands highly s
Download or read book Jet Noise Shielding from Airframe Surfaces written by Salvador Mayoral and published by . This book was released on 2010 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work investigates the potential suppression of jet noise by airframe surface shielding with application to the Hybrid Wing Body aircraft (HWB). Subscale experiments utilized a bypass-ratio-10 (BPR10) turbofan nozzle that operated at realistic cycle conditions using helium-air mixture jets. The shielding surface was a flat plate shaped in the form of a generic HWB and featured vertical fins and an adjustable elevator. Chevrons and porous wedge fan flow deflectors were incorporated into the baseline nozzle to restructure and alter the jet noise source distribution. Acoustic measurements of the unshielded and shielded jets were conducted inside an anechoic chamber using a 24-microphone apparatus composed of two polar arrays, each consisting of twelve condenser microphones. One polar array was mounted at an azimuth angle [straight phi] = 0° (downward) while the second array was mounted at [straight phi] = 60° (sideline). Noise source distribution measurements were performed by densely grouping twenty-four microphones on a linear array in the downward direction. Surveys of the jet mean flow were conducted with a fully automated three-dimensional Pitot rake traverse. The Pitot rake consists of five high-resolution Pitot probes that measure the local jet total pressure. The potential for noise suppression was quantified in terms of the estimated Effective Perceived Noise Level (EPNL), a noise metric used in aircraft certification. Acoustic results of the baseline BPR10 nozzle with the HWB shield yielded only marginal EPNL reductions, even when the engine was translated two fan diameters upstream of its nominal location. Using the estimated cumulative (downward plus sideline) EPNL reduction as a figure of merit, shielding of the baseline nozzle with the nominal shield configuration yielded a 2.5 dB reduction. Acoustic imaging of the baseline jet noise source revealed that the large fan diameter, inherent to the high bypass ratio, created a long noise source region. The integration of nozzle devices significantly improved EPNL reduction with the engine positioned at its nominal location. Application of the aggressive chevrons increased the reduction to 6.5 dB, while the best wedge configuration improved this value to 6.9 dB. Combination of wedge and aggressive chevrons yielded a benefit of 7.6 dB. Examination of high-definition noise source maps showed a direct link between insertion loss and axial location of the peak noise. Ultimately, the enhanced shielding effect from the nozzle devices resulted from translation of peak intensities upstream closer to the nozzle plug. Thus the compaction and/or redistribution of the noise source via nozzle devices are essential for effective jet noise shielding on the HWB. A proposed correlator for the noise reduction due to shielding is the average illumination angle. The average illumination angle is defined as the average angular sector between noise source and observer not intercepted by the shield. For average illumination angles less than 45 deg, the EPNL reduction exceeds 3 dB. A correlation between the acoustic and mean flow results reveal that the mean velocity field by itself cannot provide useful information for inferring the noise source location.
Download or read book The Shielding of Engine Noise by an Aircraft Wing written by E.G. Broadbent and published by . This book was released on 1970 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Technical Memorandum written by and published by . This book was released on 1986 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Alleviation of Jet Aircraft Noise Near Airports written by Jet Aircraft Noise Panel (U.S.) and published by . This book was released on 1966 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Airfoil Aeroacoustics LES and Acoustic Analogy Predictions written by William Roberto Wolf and published by Stanford University. This book was released on 2011 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of physics-based noise prediction tools for analysis of aerodynamic noise sources is of paramount importance since noise regulations have become more stringent. Direct simulation of aerodynamic noise remains prohibitively expensive for engineering problems because of the resolution requirements. Therefore, hybrid approaches that consist of predicting nearfield flow quantities by a suitable CFD simulation and farfield sound radiation by aeroacoustic integral methods are more attractive. In this work, we apply the fast multipole method (FMM) to accelerate the solution of boundary integral equation methods such as the boundary element method (BEM) and the Ffowcs Williams & Hawkings (FWH) acoustic analogy formulation. The FMM-BEM is implemented for the solution of acoustic scattering problems and the effects of non-uniform potential flows on acoustic scattering are investigated. The FMM-FWH is implemented for the solution of two and three-dimensional problems of sound propagation. The effects of flow convection and non-linear quadrupole sources are assessed through the study of sound generated by unsteady laminar flows. Finally, a hybrid methodology is applied for the investigation of airfoil noise. This study is important for the design of aerodynamic shapes such as wings and high-lift devices, as well as wind turbine blades, fans and propellers. The present investigation of airfoil self-noise generation and propagation concerns the broadband noise that arises from the interaction of turbulent boundary layers with the airfoil trailing edge and tonal noise that arises from vortex shedding generated by laminar boundary layers. Nearfield acoustic sources are computed using compressible large eddy simulation (LES) and acoustic predictions are performed by the FMM-FWH. Numerical simulations are conducted for a NACA0012 airfoil with tripped boundary layers and blunt rounded trailing edge at different Mach numbers and angles of incidence. The effects of non-linear quadrupole sources and convection are assessed. In order to validate the numerical solutions, flow simulation and acoustic prediction results are compared to experimental data available in the literature and excellent agreement is observed.
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 Alleviation of Jet Aircraft Noise Near Airports written by United States. Office of Science and Technology and published by . This book was released on 1966 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research and Technology 1986 written by and published by . This book was released on 1986 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research Technology 1999 written by and published by DIANE Publishing. This book was released on with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Advanced Aircraft Flight Performance written by Antonio Filippone and published by Cambridge University Press. This book was released on 2012-12-17 with total page 665 pages. Available in PDF, EPUB and Kindle. Book excerpt: This unique book deals with the aeroplane at several levels and aims to simulate its flight performance using computer software.
Download or read book The Shock and Vibration Digest written by and published by . This book was released on 1984 with total page 594 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book AIAA 76 531 AIAA 76 589 With omissions in numbering written by and published by . This book was released on 1976 with total page 754 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Memorandum written by and published by . This book was released on 1959 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt:
