Experimental Investigation of Noise from Interacting Axisymmetric Supersonic Jet Flows PDF Download
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Author: James Chun-Ying Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 156
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Author: James Chun-Ying Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 156
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Author: Daniel Michael Mitchell
Publisher:
ISBN:
Category :
Languages : en
Pages : 372
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This body of work describes an experimental investigation into coherent structuresand aeroacoustic feedback loops in underexpanded supersonic jets. The work includes a study of additional error terms in Particle Image Velocimetry (PIV) measurements due to the presence of shock waves within the flow, a detailed campaign of acoustic and time-resolved schlieren measurements as well as planar PIV measurements.An error analysis is conducted for the application of PIV to shock containingflows. The effect of size distribution within a seed material on measured relaxationtime is examined, with polydisperse particles of the same median diameter shown to possess a significantly higher relaxation time than their monodisperse counterpartswhen measured via a PIV algorithm. The influence of a shock wave induced velocitygradient within a PIV interrogation window on the correlation function is also examinedusing the Noiseless Cross Correlation Function of Soria (2006). The presence ofa shock is shown to introduce an artificial fluctuation into the measurement of velocity.This fluctuation is a function of the shock position, shock strength, spatial ratioand particle distribution. When the shock is located at the middle of the window,the magnitude of the fluctuation increases monotonically with increasing spatial ratio,increases asymptotically with shock strength, and decreases for increasing particle polydispersity. When the shock is located at the upstream edge of the window, the magnitude of the artificial fluctuation is highest for intermediate spatial ratios, going to zero at infinitely high and low values. In this instance particle polydispersity acts to increase the magnitude of fluctuations in measured velocity. In both cases particlepolydispersity serves to broaden the PDF of measured velocity. For the theoreticalcases presented herein, with a shock located within the interrogation window, the rootmean square of the artificial velocity fluctuations reaches values in excess of 30% of the freestream velocity. For the specific experiments presented later in the work, themagnitude of the artificial velocity fluctuation is less than 10%.Both the schlieren technique and PIV are applied to the study of the instabilitymodes of screeching axisymmetric jets. Jets at four pressure ratios: NPR = [2.2,2.6, 3.4, 4.2] are studied, and the dominant modes identified as A2, B, C and Crespectively. Three distinct modes at NPR = 2.2 are identified, one axisymmetric andtwo lateral, with screech Strouhal numbers of 0.71, 0.51 and 0.2 respectively. At NPR = 2.6 a dominant lateral mode is identified with St = 0.42. This mode proves the leastamenable to measurement with the PIV technique, as the direction of lateral oscillation precesses around the axis somewhat randomly. Helical modes at NPR = 3.4 and 4.2 are studied, with St = 0.39 and 0.35 respectively. The presence of a large Mach disk at NPR = 4.2 is not shown to qualitatively change the dynamics of the screech process.The production of discrete acoustic tones by the interaction between embeddedshocks and convected vortices is directly visualized. The motion of vortices is seen tocreate a disturbance wave at the shock reflection point of an upstream shock cell, this disturbance convects to the jet core and forms the basis for an evanescent convecting shockwave downstream. The flattening of this shock wave during the passage of the vortex results in a strong acceleration of the shock-tip, which moves in a whip-like manner and generates a strong upstream travelling acoustic wave. Analysis of the skewness and kurtosis of the axial velocity probability density functions is shown to be able to identify locations of intense sound generation. The second, third and fourth shock cells are shown to be the dominant noise sources.
Author:
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Category : Jet planes
Languages : en
Pages : 52
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Author: Russell Powers
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Category :
Languages : en
Pages :
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The noise produced by the supersonic, high temperature jets that exhaust from military aircraft is becoming a hazard to naval personnel and a disturbance to communities near military bases. Methods to reduce the noise produced from these jets in a practical full-scale environment are difficult. The development and analysis of distributed nozzle blowing for the reduction of radiated noise from supersonic jets is described. Model scale experiments of jets that simulate the exhaust jets from typical low-bypass ratio military jet aircraft engines during takeoff are performed. Fluidic inserts are created that use distributed blowing in the divergent section of the nozzle to simulate mechanical, hardwall corrugations, while having the advantage of being an active control method. This research focuses on model scale experiments to better understand the fluidic insert noise reduction method. Distributed blowing within the divergent section of the military-style convergent divergent nozzle alters the shock structure of the jet in addition to creating streamwise vorticity for the reduction of mixing noise. Enhancements to the fluidic insert design have been performed along with experiments over a large number of injection parameters and core jet conditions. Primarily military-style round nozzles have been used, with preliminary measurements of hardwall corrugations and fluidic inserts in rectangular nozzle geometries also performed. It has been shown that the noise reduction of the fluidic inserts is most heavily dependent upon the momentum flux ratio between the injector and core jet. Maximum reductions of approximately 5.5 dB OASPL have been observed with practical mass flow rates and injection pressures. The first measurements with fluidic inserts in the presence of a forward flight stream have been performed. Optimal noise reduction occurs at similar injector parameters in the presence of forward flight. Fluidic inserts in the presence of a forward flight stream were observed to reduce the peak mixing noise below the already reduced levels by nearly 4 dB OASPL and the broadband shock-associated noise by nearly 3 dB OASPL. Unsteady velocity measurements are used to complement acoustic results of jets with fluidic inserts. Measured axial turbulence intensities and mean axial velocity are examined to illuminate the differences in the flow field from jets with fluidic inserts. Comparisons of laser Doppler measurements with RANS CFD simulations are shown with good agreement. Analysis of the effect of spatial turbulence on the measured quantities is performed. Experimental model scale measurements of jets with and without fluidic inserts over a simulated carrier deck are presented. The model carrier environment consists of a ground plane of adjustable distance below the jet, and a simulated jet blast deflector similar to those found in practice. Measurements are performed with far-field microphones, near-field microphones, and unsteady pressure sensors. The constructive and destructive interference that results from the interaction of the direct and reflected sound waves is observed and compared with results from free jets. The noise reduction of fluidic inserts in a realistic carrier deck environment with steering of the ``quiet planes'' is examined. The overall sound pressure level in heat-simulated jets is reduced by 3-5 dB depending on the specific angle and ground plane height. Jets impinging upon a modeled jet blast deflector are tested in addition to jets solely in the presence of the carrier deck. Observed modifications to the acoustic field from the presence of the jet blast deflector include downstream acoustic shielding and low frequency augmentation. The region of maximum noise radiation for heat-simulated jets from nozzles with fluidic inserts impinging on the jet blast deflector is reduced in overall sound pressure level by 4-7 dB. This region includes areas where aircraft carrier personnel are located.
Author:
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Category : Aeronautics
Languages : en
Pages : 704
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Author: Seyyed Saman Salehian
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 536
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"The noise generated by supersonic jet is of primary interest in the high-speed flight. In several flight conditions jet exhaust of the propulsion system interacts with solid surfaces. For example, jet impingement on ground for a rocket lift-off, or interactions influenced by the integration of the engine with the airframe. Such complex applications require consideration of the role of acoustic-surface interactions on the noise generation of the jet and its radiation. Numerical analysis of supersonic jet noise involved in these scenarios is investigated by employing Hybrid Large Eddy Simulation - Unsteady Reynolds Averaged Simulation approach to model turbulence. First, the supersonic impinging jet noise reduction using aqueous injectors is investigated. The technique employed to suppress impingement noise, involves injecting liquid water from the ground surface. The Volume of Fluid model is adopted to simulate the two phase flow. The flow field and acoustic results agree well with the existing experimental data. The possible mechanisms of noise reduction by water injection are investigated. Second, supersonic jet noise reduction by employing the shielding effect of a flat plate parallel to the jet is investigated. The numerical simulations model the shielding effect of the flat plate on the acoustics of supersonic jet, and results agree with the corresponding experimental data. The physical mechanisms involved in the flow-surface interactions are investigated. With understanding these mechanisms, a slightly wavy plate is proposed including theoretical background to determine the parameters needed for the way wall to provide acoustic reduction efficiently. Results show that the proposed wavy shield can effectively reduce both the level and extent of the jet noise source as compared to that of a flat shield."--Abstract.
Author:
Publisher:
ISBN:
Category : Government publications
Languages : en
Pages : 1638
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Author: Harvey H. Hubbard
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ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 620
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Author:
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ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 400
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Author:
Publisher:
ISBN:
Category : Government publications
Languages : en
Pages : 1388
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