scholarly journals Wavepacket models for supersonic jet noise

2014 ◽  
Vol 742 ◽  
pp. 71-95 ◽  
Author(s):  
Aniruddha Sinha ◽  
Daniel Rodríguez ◽  
Guillaume A. Brès ◽  
Tim Colonius
Keyword(s):  
Large Scale ◽  
Near Field ◽  
Supersonic Jet ◽  
Low Frequency ◽  
Linear Instability ◽  
Mean Flow ◽  
Parabolized Stability Equations ◽  
Eddy Simulation ◽  
Field Noise ◽  
Propagation Technique

AbstractGudmundsson and Colonius (J. Fluid Mech., vol. 689, 2011, pp. 97–128) have recently shown that the average evolution of low-frequency, low-azimuthal modal large-scale structures in the near field of subsonic jets are remarkably well predicted as linear instability waves of the turbulent mean flow using parabolized stability equations. In this work, we extend this modelling technique to an isothermal and a moderately heated Mach 1.5 jet for which the mean flow fields are obtained from a high-fidelity large-eddy simulation database. The latter affords a rigourous and extensive validation of the model, which had only been pursued earlier with more limited experimental data. A filter based on proper orthogonal decomposition is applied to the data to extract the most energetic coherent components. These components display a distinct wavepacket character, and agree fairly well with the parabolized stability equations model predictions in terms of near-field pressure and flow velocity. We next apply a Kirchhoff surface acoustic propagation technique to the near-field pressure model and obtain an encouraging match for far-field noise levels in the peak aft direction. The results suggest that linear wavepackets in the turbulence are responsible for the loudest portion of the supersonic jet acoustic field.

Computation of jet mixing noise due to coherent structures: the plane jet case

1997 ◽  
Vol 335 ◽  
pp. 261-304 ◽  
Author(s):  
F. BASTIN ◽  
P. LAFON ◽  
S. CANDEL
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Supersonic Jet ◽  
Low Frequency ◽  
Coherent Motion ◽  
Mean Flow ◽  
Jet Mixing ◽  
Deterministic Modelling ◽  
Plane Jets ◽  
Mixing Noise

A computational approach to the prediction of jet mixing noise is described. It is based on Lighthill's analogy, used together with a semi-deterministic modelling of turbulence (SDM), where only the large-scale coherent motion is evaluated. The features of SDM are briefly illustrated in the case of shear layers, showing that suitable descriptions of the mean flow and of the large-scale fluctuations are obtained. Aerodynamic calculations of two cold fully expanded plane jets at Mach numbers 0.50 and 1.33 are then carried out. The numerical implementation of Lighthill's analogy is described and different integral formulations are compared for the two jets. It is shown that the one expressed in a space–time conjugate (κ, ω)-plane is particularly convenient and allows a simple geometrical interpretation of the computations. Acoustic results obtained with this formulation are compared to relevant experimental data. It is concluded that the radiation of subsonic jets cannot be explained only by the contribution of the turbulent coherent motion. In this case, directivity effects are well recovered but the acoustic spectra are too narrow and limited to the low-frequency range. In contrast at Mach number 1.33, especially in the forward quadrant, results are satisfactory, showing that coherent structures indeed provide the main source of supersonic jet mixing noise.

A proposed wavy shield for suppression of supersonic jet noise utilizing reflections

2021 ◽  
Vol 20 (1-2) ◽  
pp. 4-34
Author(s):  
Reda R Mankbadi ◽  
Saman Salehian
Keyword(s):  
Large Scale ◽  
Flat Surface ◽  
Near Field ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Dominant Frequency ◽  
Wavy Surface ◽  
Initial Region ◽  
Reflected Waves ◽  
Free Jet

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

Numerical Simulations of Isothermal Flow in a Swirl Burner

2006 ◽  
Author(s):  
Manuel Garci´a-Villalba ◽  
Jochen Fro¨hlich ◽  
Wolfgang Rodi
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Reacting Flow ◽  
Swirl Burner ◽  
Eddy Simulation ◽  
Pressure Time ◽  
Time Signals ◽  
Flow Oscillations ◽  
Conditional Averaging ◽  
Annular Jets

In this paper; the non-reacting flow in a swirl burner is studied using Large Eddy Simulation. The configuration consists of two unconfined co-annular jets at a Reynolds number of 81500. The flow is characterized by a Swirl number of 0.93. Two cases are studied in the paper differing with respect to the axial location of the inner pilot jet. It was observed in a companion experiment (Bender and Bu¨chner, 2005) that when the inner jet is retracted the flow oscillations are considerably amplified. This is also found in the present simulations. Large-scale coherent structures rotating at a constant rate are observed when the inner jet is retracted. The rotation of the structures leads to vigorous oscillations in the velocity and pressure time signals recorded at selected points in the flow. In addition, the mean velocities, the turbulent fluctuations and the frequency of the oscillations are in good agreement with the experiments. A conditional averaging procedure is used to perform a detailed analysis of the physics leading to the low-frequency oscillations.

Crackle Noise in Heated Supersonic Jets

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Joseph W. Nichols ◽  
Sanjiva K. Lele ◽  
Frank E. Ham ◽  
Steve Martens ◽  
John T. Spyropoulos
Keyword(s):  
Large Scale ◽  
Supersonic Jet ◽  
Supersonic Jets ◽  
Scale Model ◽  
Positive Pressure ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Total Temperature ◽  
Large Scale Flow ◽  
Large Eddies

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with N-shaped waveforms involving a shocklike compression and, thus, is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments (Martens et al., 2011, “The Effect of Chevrons on Crackle—Engine and Scale Model Results,” Proceedings of the ASME Turbo Expo, Paper No. GT2011-46417) have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through a high-fidelity large-eddy simulation (LES) of a hot supersonic jet of Mach number 1.56 and a total temperature ratio of 3.65. We use the LES solver CHARLES developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fully-unstructured meshes.

Experiments on the flow and acoustic properties of a moderate-Reynolds-number supersonic jet

1982 ◽  
Vol 116 ◽  
pp. 123-156 ◽  
Author(s):  
T. R. Troutt ◽  
D. K. Mclaughlin
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Near Field ◽  
Acoustic Properties ◽  
Generation Model ◽  
Initial Growth ◽  
Noise Generation ◽  
Mean Flow ◽  
Potential Core ◽  
Moderate Reynolds Number

An experimental investigation of the flow and acoustic properties of a moderate-Reynolds-number (Re = 70000), Mach number M = 2·1, axisymmetric jet has been performed. These measurements extended the experimental studies conducted previously in this laboratory to a higher-Reynolds-number regime where the flow and acoustic processes are considerably more complex. In fact, mean-flow and acoustic properties of this jet were determined to be closely comparable to published properties of high-Reynolds-number jets.The major results of the flow-field measurements demonstrate that the jet shear annulus is unstable over a broad frequency range. The initial growth rates and wavelengths of these instabilities as measured by a hot wire were found to be in reasonable agreement with linear stability theory predictions. Also, in agreement with subsonic-jet results, the potential core of the jet was found to be most responsive to excitation at frequencies near a Strouhal number of S = 0·3. The overall development of organized disturbances around S = 0·2 seems to agree in general with calculations performed using the instability theory originally developed by Morris and Tam.The acoustic near field was characterized in terms of sound-pressure level and directivity for both natural and excited (pure-tone) jets. In addition, propagation direction and azimuthal character of dominant spectral components were also measured. It was determined that the large-scale flow disturbances radiate noise in a directional pattern centred about 30° from the jet axis. The noise from these disturbances appears from simple ray tracing to be generated primarily near the region of the jet where the coherent fluctuations saturate in amplitude and begin to decay. It was also determined that the large-scale components of the near-field sound are made up predominately of axisymmetric (n = 0) and helical (n = ±1) modes. The dominant noise-generation mechanism appears to be a combination of Mach-wave generation and a process associated with the saturation and disintegration of the large-scale instability. Finally, the further development of a noise-generation model of the instability type appears to hold considerable promise.

Impact of Mechanical Chevrons on Supersonic Jet Flow and Noise

2009 ◽  
Author(s):  
K. Kailasanath ◽  
Junhui Liu ◽  
Ephraim Gutmark ◽  
David Munday ◽  
Steven Martens
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Near Field ◽  
Supersonic Jet ◽  
Initial Step ◽  
Nozzle Geometry ◽  
Jet Flows ◽  
Flow Conditions ◽  
Nozzle Geometries ◽  
The Impact

In this paper, we present observations on the impact of mechanical chevrons on modifying the flow field and noise emanated by supersonic jet flows. These observations are derived from both a monotonically integrated large-eddy simulation (MILES) approach to simulate the near fields of supersonic jet flows and laboratory experiments. The nozzle geometries used in this research are representative of practical engine nozzles. A finite-element flow solver using unstructured grids allows us to model the nozzle geometry accurately and the MILES approach directly computes the large-scale turbulent flow structures. The emphasis of the work is on “off-design” or non-ideally expanded flow conditions. LES for several total pressure ratios under non-ideally expanded flow conditions were simulated and compared to experimental data. The agreement between the predictions and the measurements on the flow field and near-field acoustics is good. After this initial step on validating the computational methodology, the impact of mechanical chevrons on modifying the flow field and hence the near-field acoustics is being investigated. This paper presents the results to date and further details will be presented at the meeting.

Coherent structures and dominant frequencies in a turbulent three-dimensional diffuser

2012 ◽  
Vol 699 ◽  
pp. 320-351 ◽  
Author(s):  
Johan Malm ◽  
Philipp Schlatter ◽  
Dan S. Henningson
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Bulk Velocity ◽  
Time Signal ◽  
Mean Flow ◽  
The Mean ◽  
Dominant Frequencies

AbstractDominant frequencies and coherent structures are investigated in a turbulent, three-dimensional and separated diffuser flow at $\mathit{Re}= 10\hspace{0.167em} 000$ (based on bulk velocity and inflow-duct height), where mean flow characteristics were first studied experimentally by Cherry, Elkins and Eaton (Intl J. Heat Fluid Flow, vol. 29, 2008, pp. 803–811) and later numerically by Ohlsson et al. (J. Fluid Mech., vol. 650, 2010, pp. 307–318). Coherent structures are educed by proper orthogonal decomposition (POD) of the flow, which together with time probes located in the flow domain are used to extract frequency information. The present study shows that the flow contains multiple phenomena, well separated in frequency space. Dominant large-scale frequencies in a narrow band $\mathit{St}\equiv fh/ {u}_{b} \in [0. 0092, 0. 014] $ (where $h$ is the inflow-duct height and ${u}_{b} $ is the bulk velocity), yielding time periods ${T}^{\ensuremath{\ast} } = T{u}_{b} / h\in [70, 110] $, are deduced from the time signal probes in the upper separated part of the diffuser. The associated structures identified by the POD are large streaks arising from a sinusoidal oscillating motion in the diffuser. Their individual contributions to the total kinetic energy, dominated by the mean flow, are, however, small. The reason for the oscillating movement in this low-frequency range is concluded to be the confinement of the flow in this particular geometric set-up in combination with the high Reynolds number and the large separated zone on the top diffuser wall. Based on this analysis, it is shown that the bulk of the streamwise root mean square (r.m.s.) value arises due to large-scale motion, which in turn can explain the appearance of two or more peaks in the streamwise r.m.s. value. The weak secondary flow present in the inflow duct is shown to survive into the diffuser, where it experiences an imbalance with respect to the upper expanding corners, thereby giving rise to the asymmetry of the mean separated region in the diffuser.

LES Predictions of Jet Noise for a Pylon-Mounted Dual Stream Nozzle and Jet Surface Interactions

2016 ◽  
Author(s):  
P. Vogel ◽  
J. Bin ◽  
N. Sinha
Keyword(s):  
Supersonic Jet ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Acoustic Source ◽  
Noise Sources ◽  
Surface Time ◽  
Acoustic Source Localization ◽  
Jet Nozzle ◽  
Field Noise

An end-to-end LES/FW-H noise prediction model has been demonstrated and validated with acoustic and flowfield data from a dual stream nozzle with pylon experiment conducted at NASA GRC using their Jet Engine Simulator (JES) geometry. Results show a large region of high turbulent kinetic energy (TKE) in the wake of the pylon. Acoustic Source Localization (ASL) studies using our numerical phased array methodology show this wake region to be the principle location of low frequency noise sources while higher frequency sources occur nearer to the nozzle lips. Numerical simulations have also been conducted on Jet-Surface Interaction (JSI) effects of a supersonic jet exhausting parallel to a finite surface. Time-averaged LES data and far-field noise predictions have been obtained for multiple surface locations as well as for an isolated jet nozzle. For upstream observers located below the surface, results show an increase in low-frequency noise over what was predicted for the isolated nozzle due to JSI effects and decrease in high-frequency noise due to shielding. This was significantly more pronounced for an over-expanded jet than for an under-expanded jet, an effect that was primarily attributed to the shorter core length of the over-expanded jet.

scholarly journals The Contribution of Striations to the Eddy Energy Budget and Mixing: Diagnostic Frameworks and Results in a Quasigeostrophic Barotropic System with Mean Flow

2015 ◽  
Vol 45 (8) ◽  
pp. 2095-2113 ◽  
Author(s):  
Ru Chen ◽  
Glenn R. Flierl
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Ocean Model ◽  
Invariance Property ◽  
Mean Flow ◽  
Eddy Diffusivities ◽  
Energy Cascades ◽  
The Mean ◽  
Flow Theories ◽  
Noise Forcing

AbstractLow-frequency oceanic motions have banded structures termed “striations.” Since these striations embedded in large-scale gyre flows can have large amplitudes, the authors investigated the effect of mean flow on their directions as well as their contribution to energetics and mixing using a β-plane, barotropic, quasigeostrophic ocean model. In spite of the model simplicity, striations are always found to exist regardless of the imposed barotropic mean flow. However, their properties are sensitive to the mean flow. Rhines jets move with the mean flow and are not necessarily striations. If the meridional component of the mean flow is large, Rhines jets become high-frequency motions; low-frequency striations still exist, but they are nonzonal, have small magnitudes, and contribute little to energetics and mixing. Otherwise, striations are zonal, dominated by Rhines jets, and contribute significantly to energetics and mixing. This study extends the theory of β-plane, barotropic turbulence, driven by white noise forcing at small scales, to include the effect of a constant mean flow. Theories developed in this study, based upon the Galilean invariance property, illustrate that the barotropic mean flow has no effect on total mixing rates, but does affect the energy cascades in the frequency domain. Diagnostic frameworks developed here can be useful to quantify the striations’ contribution to energetics and mixing in the ocean and more realistic models. A novel diagnostic formula is applied to estimating eddy diffusivities.

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