A Technique and Computer Program for Predicting Far Field Noise Levels from Piping Runs

1980 ◽  
Vol 102 (3) ◽  
pp. 136-143
Author(s):  
M. F. Ajax
Keyword(s):  
Computer Program ◽  
Acoustic Energy ◽  
Far Field ◽  
Octave Band ◽  
Noise Levels ◽  
Field Noise ◽  
Intensity Decay

Acoustic energy as radiated from effective incremental cylindrical surfaces is considered, which during the course of initial propagation are assumed to become hemisperhical and divergent. These are summed along piping runs under chosen gradient conditions representing an intensity decay along the pipe. A computer program for scanning the geometry of these incremental radiating surfaces is provided to include the effect of barriers in the line of propagation. Printout is both octave-band and “A” weighted.

Directional Noise Reduction via Asymmetric Downstream Fluidic Injection

2017 ◽  
Author(s):  
Pankaj Rajput ◽  
Sunil Kumar
Keyword(s):  
Noise Reduction ◽  
Turbulent Mixing ◽  
Near Field ◽  
Acoustic Energy ◽  
Far Field ◽  
High Momentum ◽  
Mean Flow ◽  
Flow Measurements ◽  
Mixing Noise ◽  
Field Noise

The main aim of this investigation is to analyze directional noise reduction resulting from asymmetric high momentum fluidic injection downstream of a Mach 0.9 nozzle. Jet noise has been identified as one of the primary obstacles to increasing commercial aviation capacity. Microjets in cross flow are known to enhance turbulent mixing in the shear layer due to the induced stream-wise vortices. This enhanced mixing can be used for reorganizing the spatial distribution of acoustic energy. Targeted reduction in the downward-emitted turbulent mixing noise can be achieved by strategically injecting high momentum fluid downstream of the jet exhaust. Detailed Large Eddy Simulations were performed on a hybrid block structured-unstructured mesh to generate the flow field which was then used for near field and far field noise computation. Aeroacoustic analogy based formulation was used for computing far-field noise estimation. Benchmark cases were validated with preexisting experimental data sets. Mean flow measurements suggest shorter jet core lengths due to the enhanced mixing resulting from fluidic injection. The induced asymmetry due to the fluidic injection gives rise to an asymmetric acoustic field leading to targeted directional noise reduction in the far field as measured by pressure probes.

Near and Far-Field Investigations of Supersonic Jet Noise Predictions Using a Coupled LES and FW-H Equation Method

2011 ◽  
Author(s):  
James P. Erwin ◽  
Neeraj Sinha
Keyword(s):  
Supersonic Jet ◽  
Turbine Engines ◽  
Far Field ◽  
Noise Levels ◽  
Physical Acoustics ◽  
Aircraft Carrier ◽  
Eddy Simulation ◽  
Field Investigations ◽  
Large Eddy ◽  
Field Noise

The hot supersonic exhausts of gas turbine engines on military aircraft generate dangerously high noise levels. The noise levels associated with operating these engines are harmful to aircraft carrier deck personnel as well as detrimental to ship and aircraft structures. In this paper, the supersonic jet exhaust is simulated using Large Eddy Simulation (LES), and the Ffowcs Williams and Hawkings (FW-H) equation transforms the LES solution to an acoustic solution in the far-field. A Mach 1.5 laboratory jet test at United Technologies Research Center - Acoustics Research Tunnel is used as validation for the LES/FW-H method. A grid refinement study was performed with the objective of determining the requirements for accurate noise predictions. The finest grid resolution yields the best near and far-field acoustic prediction. A second LES/FW-H validation case is shown for a twin jet experiment that was performed in the anechoic chamber at University of Mississippi’s National Center for Physical Acoustics (NCPA). The LES/FW-H method is applied to the higher complexity heated twin jet with faceted nozzle profiles, demonstrating the applicability of the method over a wider range of flow regimes. The far-field noise prediction agrees very well with the NCPA experiment, including the prediction of broadband shock associated noise and jet screech.

scholarly journals An analytic solution for the noise generated by gust–aerofoil interaction for plates with serrated leading edges

2018 ◽  
Vol 853 ◽  
pp. 515-536 ◽  
Author(s):  
Lorna J. Ayton ◽  
Jae Wook Kim
Keyword(s):  
Analytic Solution ◽  
Separation Of Variables ◽  
Leading Edge ◽  
Acoustic Energy ◽  
Destructive Interference ◽  
Far Field ◽  
Numerical Predictions ◽  
Leading Edges ◽  
Field Noise ◽  
Good Agreement

This paper presents an analytic solution for the sound generated by an unsteady gust interacting with a semi-infinite flat plate with a serrated leading edge in a background steady uniform flow. Viscous and nonlinear effects are neglected. The Wiener–Hopf method is used in conjunction with a non-orthogonal coordinate transformation and separation of variables to permit analytical progress. The solution is obtained in terms of a modal expansion in the spanwise coordinate; however, for low- and mid-range incident frequencies only the zeroth-order mode is seen to contribute to the far-field acoustics, therefore the far-field noise can be quickly evaluated. The solution gives insight into the potential mechanisms behind the reduction of noise for plates with serrated leading edges compared to those with straight edges, and predicts a logarithmic dependence between the tip-to-root serration height and the decrease of far-field noise. The two mechanisms behind the noise reduction are proposed to be an increased destructive interference in the far field, and a redistribution of acoustic energy from low cut-on modes to higher cut-off modes as the tip-to-root serration height is increased. The analytic results show good agreement in comparison with experimental measurements. The results are also compared against nonlinear numerical predictions where good agreement is also seen between the two results as frequency and tip-to-root ratio are varied.

scholarly journals Jet-Surface Interaction Test: Far-Field Noise Results

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Clifford A. Brown
Keyword(s):  
High Speed ◽  
Radial Distance ◽  
Jet Noise ◽  
Surface Interaction ◽  
Shielding Effect ◽  
Noise Prediction ◽  
Far Field ◽  
Wide Range ◽  
Field Noise ◽  
Surface Length

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet-Surface Interaction Tests are intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. The initial goal is to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet-surface interaction is creating additional noise, and (2) determine regions of interest for future, more detailed, tests. To meet these objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface length was varied between 2 and 20 jet diameters downstream of the nozzle exit. Similarly, the radial distance from the jet centerline to the surface face was varied between 1 and 16 jet diameters. Far-field and phased array noise data were acquired at each combination of surface length and radial location using two nozzles operating at jet exit conditions across several flow regimes: subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic. The far-field noise results, discussed here, show where the jet noise is partially shielded by the surface and where jet-surface interaction noise dominates the low frequency spectrum as a surface extends downstream and approaches the jet plume.

Implementation of the Ffowcs Williams-Hawkings Equation: Predicting the Far Field Noise From Airfoils While Using Boundary Layer Tripping Mechanisms

2018 ◽  
Author(s):  
Andrew L. Bodling ◽  
Anupam Sharma
Keyword(s):  
Boundary Layer ◽  
High Frequency ◽  
Permeable Surface ◽  
Far Field ◽  
Trailing Edge ◽  
Extraneous Noise ◽  
Field Noise ◽  
High Frequency Waves

A study was done to investigate how boundary layer tripping mechanisms can affect the ability of a permeable surface FW-H solver to predict the far field noise emanating from an airfoil trailing edge. The far field noise in a baseline airfoil as well as the baseline airfoil fitted with fin let fences was analyzed. Two numerical boundary layer tripping mechanisms were implemented. The results illustrated the importance of choosing a permeable integration surface that is outside any high frequency waves emanating from the trip region. The results also illustrated the importance of choosing a boundary layer tripping mechanism that minimizes any extraneous noise so that an integration surface can be taken close to the airfoil.

scholarly journals A fast computational model for near- and far-field noise prediction due to offshore pile driving

2021 ◽  
Vol 149 (3) ◽  
pp. 1772-1790
Author(s):  
Yaxi Peng ◽  
Apostolos Tsouvalas ◽  
Tasos Stampoultzoglou ◽  
Andrei Metrikine
Keyword(s):  
Computational Model ◽  
Pile Driving ◽  
Noise Prediction ◽  
Far Field ◽  
Field Noise

Relationships Between Acoustic Radiation Modes, Complex Acoustic Power, and Radiation Efficiency

1997 ◽  
Author(s):  
Pei-Tai Chen
Keyword(s):  
Acoustic Radiation ◽  
Acoustic Power ◽  
Radiation Efficiency ◽  
Acoustic Energy ◽  
Normal Velocity ◽  
Far Field ◽  
Surface Complex ◽  
Surface Integral ◽  
Complex Power ◽  
Mass Spring

Abstract The paper explores the physical meaning underlying the surface complex acoustic power of a vibrating body, and its relationship to radiation efficiency under mono-frequency oscillations. The vibrating can be the entire wetted surface, or only a part of the surface with the remaining surface being held rigid. The surface complex acoustic power can be computed by the surface integral of pressure multiplying the complex conjugate of normal velocity. Based on the Gaussian Divergence theorem, it is shown that the real part of the complex power is the power radiated into a far field, while that the imaginary part pertains to the volume integral of the difference between the acoustic kinetic energy density with the potential energy density over the volume between the vibrating surface and the far field. The dynamical behavior of the acoustic field can be viewed as an infinite degree of freedom mass/spring/dashpot system, where the mass and spring are the inertia effects and acoustic compression effects of the acoustic particles and the dashpot is due to the plane wave relationship of the pressure waves at the far field that the acoustic energy propagates away from the acoustic field. By the model of the mass /spring/dashpot system, the phase angle of the complex acoustic power is identified as an indication of the ability of the vibrating surface to radiate acoustic power. The phase angle of the complex power depends on the distribution of the surface normal velocity. In order to study the normal velocity profile in relation to the ability to radiate acoustic energy, the previously established radiation mode (Chen and Ginsberg, 1995) is introduced and extended to situations in which a part of the surface is held rigid. An orthogonal condition for the velocity radiation modes is also established such that arbitrary velocity profiles can be decomposed into radiation modes. The acoustic modal radiation efficiency, defined as the radiated modal acoustic power divided by the surface integral of mean square normal velocity, is investigated in terms of the acoustic eigenvalue of that mode. Several different geometries of vibrating bodies are used to demonstrate the correlation of radiation efficiencies to eigenvalues of radiation modes, which include a rectangular baffled vibrating membrane, a box with only one of the six surfaces vibrating, a slender spheroidal body, and a spherical body. This correlation of acoustic radiation characteristics for different geometries is also demonstrated for a spheroidal body vibrating at some areas with other areas being held rigid.

scholarly journals Bioinspired aerofoil adaptations: the next steps for theoretical models

2019 ◽  
Vol 377 (2159) ◽  
pp. 20190070 ◽  
Author(s):  
Lorna J. Ayton
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Theoretical Modelling ◽  
Experimental Measurements ◽  
Far Field ◽  
Acoustic Analogy ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Theoretical Predictions ◽  
Field Noise

The extended introduction in this paper reviews the theoretical modelling of leading- and trailing-edge noise, various bioinspired aerofoil adaptations to both the leading and trailing edges of blades, and how these adaptations aid in the reduction of aerofoil–turbulence interaction noise. Attention is given to the agreement between current theoretical predictions and experimental measurements, in particular, for turbulent interactions at the trailing edge of an aerofoil. Where there is a poor agreement between theoretical models and experimental data the features neglected from the theoretical models are discussed. Notably, it is known that theoretical predictions for porous trailing-edge adaptations do not agree well with experimental measurements. Previous works propose the reason for this: theoretical models do not account for surface roughness due to the porous material and thus omit a key noise source. The remainder of this paper, therefore, presents an analytical model, based upon the acoustic analogy, to predict the far-field noise due to a rough surface at the trailing edge of an aerofoil. Unlike previous roughness noise models which focus on roughness over an infinite wall, the model presented here includes diffraction by a sharp edge. The new results are seen to be in better agreement with experimental data than previous models which neglect diffraction by an edge. This new model could then be used to improve theoretical predictions for far-field noise generated by turbulent interactions with a (rough) porous trailing edge. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

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