Abstract We study the velocity fields of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers. The objective is to educe wavepackets in such flows and explore their relationship radiated sound. field measured using a hot-wire anemometer stereoscopic, time-resolved PIV system. can be decomposed into frequency azimuthal Fourier modes. low-angle sound radiation synchronously microphone ring array. Consistent previous observations, wavenumber...

Abstract We present experimental results for the acoustic field of jets with Mach numbers between 0.35 and 0.6. An azimuthal ring array six microphones, whose polar angle, $\theta $ , was progressively varied, allows decomposition pressure into Fourier modes. In agreement past observations, sound low angles (measured respect to jet axis) is found be dominated by axisymmetric mode, particularly at peak Strouhal number. The mode can clearly associated an axially non-compact source, in form a...

To investigate the effects of nozzle-exit conditions on jet flow and sound fields, large-eddy simulations an isothermal Mach 0.9 issued from a convergent-straight nozzle are performed at diameter-based Reynolds number $1\times 10^{6}$ . The feature near-wall adaptive mesh refinement, synthetic turbulence wall modelling inside nozzle. This leads to fully turbulent boundary layers results in significant improvements for field predictions compared with those obtained typical approach based...

The purpose of this paper is to characterize and model waves that are observed within the potential core subsonic jets relate them previously tones in near-nozzle region. detected data from a large-eddy simulation Mach 0.9 isothermal jet modelled using parallel weakly non-parallel linear modal analysis Euler equations linearized about turbulent mean flow, as well simplified models based on cylindrical vortex sheet acoustic modes soft duct. In addition Kelvin–Helmholtz instability waves,...

Coherent features of a turbulent Mach 0.9, Reynolds number $10^{6}$ jet are educed from high-fidelity large eddy simulation. Besides the well-known Kelvin–Helmholtz instabilities shear layer, new class trapped acoustic waves is identified in potential core. A global linear stability analysis based on mean flow conducted. The form branches discrete eigenvalues spectrum, and corresponding modes accurately match structures. Discrete occur hierarchy determined by their radial axial order. local...

Motivated by the problem of jet–flap interaction noise, we study tonal dynamics that occurs when an isothermal turbulent jet grazes a sharp edge. We perform hydrodynamic and acoustic pressure measurements to characterise tones as function Mach number streamwise edge position. The observed distribution spectral peaks cannot be explained using usual edge-tone model, in which resonance is underpinned coupling between downstream-travelling Kelvin–Helmholtz wavepackets upstream-travelling sound...

Organized structures in turbulent jets can be modeled as wavepackets. These are characterized by spatial amplification and decay, both of which related to stability mechanisms, they coherent over several jet diameters, thereby constituting a noncompact acoustic source that produces distinctive directivity the field. In this review, we use simplified model problems discuss salient features turbulent-jet wavepackets their modeling frameworks. Two classes considered. The first, refer kinematic,...

Three amplification mechanisms present in turbulent jets, namely lift-up, Kelvin-Helmholtz, and Orr, are characterized via global resolvent analysis spectral proper orthogonal decomposition (SPOD) over a range of Mach numbers. The lift-up mechanism was recently identified jets local by Nogueira et al. (J. Fluid Mech., vol. 873, 2019, pp. 211-237) at low Strouhal number ($St$) non-zero azimuthal wavenumbers ($m$). In these limits, SPOD data from high-fidelity simulations reveals streamwise...

Direct numerical simulations, performed with a high-order spectral-element method, are used to study coherent structures in turbulent pipe flow at friction Reynolds numbers $Re_{\tau} = 180$ and $550$. The database was analysed using spectral proper orthogonal decomposition (SPOD) identify energetically dominant structures, most of which turn out be streaks quasi-streamwise vortices. To understand how such can modelled, the linear responses harmonic forcing were computed singular value...

Abstract Wavepackets obtained by a linear stability analysis of the turbulent mean flow were shown in recent works to agree closely with some relevant statistics jets, such as power spectral densities and averaged phases fluctuations. However, when wavepacket models used calculate far-field sound, satisfactory agreement was only for flows that supersonic relative ambient speed sound; attempts subsonic led errors more than an order magnitude. We investigate here reasons discrepancies...

Streaks have been found to be an important part of wall-turbulence dynamics. In this paper, we extend the analysis for unbounded shear flows, in particular a Mach 0.4 round jet, using measurements taken dual-plane, time-resolved, stereoscopic particle image velocimetry (PIV) at pairs jet cross-sections, allowing evaluation cross-spectral density streamwise velocity fluctuations resolved into azimuthal Fourier modes. From results, two analyses are performed: wavenumber spectra (assuming...

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Self-similarity of wall-attached coherent structures in a turbulent channel at $Re_\tau =543$ is explored by means resolvent analysis. In this modelling framework, are understood to arise as response the linearised mean-flow operator generalised frequency-dependent Reynolds stresses, considered act an endogenous forcing. We assess self-similarity both flow and associated The former educed from direct numerical simulation data finding field correlated with wall shear, whereas latter...

Linear instability waves, or wavepackets, are key building blocks for the jet-noise problem. It has been shown in previous work that linear models correctly predict evolution of axisymmetric wavepackets up to end potential core subsonic turbulent jets. Beyond this station, fail, and nonlinearity is likely missing piece. The essential underlying nonlinear mechanisms unknown, it remains unclear how these should be incorporated a reduced-order model. interactions considered as an ‘external’...

Abstract This work belongs to the ongoing debate surrounding mechanism responsible for low-angle sound emission from subsonic jets. The flow, simulated by large eddy simulation (Bogey & Bailly, Comput. Fluids , vol. 35 (10), 2006a, pp. 1344–1358), is a Mach 0.9 jet with Reynolds number, based on exit diameter, of $4\ensuremath{\times} 1{0}^{5} $ . A methodology implemented educe, explore and model flow motions associated radiation. eduction procedure, which frequency–wavenumber filtering...

We present a numerical method to compute the acoustic field scattered by finite perforated elastic plates. A boundary element is developed solve Helmholtz equation subjected conditions related plate vibration. These are recast in terms of vibration modes and its porosity, which enables direct solution procedure. parametric study performed for two-dimensional problem whereby cantilevered scatters sound from point quadrupole near free edge. Both elasticity porosity tend diminish sound,...

Installed jet noise is studied by means of a simplified configuration comprising flat plate in the vicinity round jet. The effects Mach number, jet-plate radial distance, and trailing-edge sweep angle are explored. Acoustic measurements performed using traversable 18-microphone azimuthal array, providing pressure data at 360 points on cylindrical surface surrounding system. Key observations include decrease, with increasing relative level scattered field comparison to uninstalled jet; an...

We investigate source mechanisms for subsonic jet noise using experimentally obtained datasets of high-Reynolds-number Mach 0.4 and 0.6 turbulent jets. The focus is on the axisymmetric mode which dominates downstream sound radiation low polar angles frequency range at peak occurs. A linearized Euler equation (LEE) solver with an inflow boundary condition used to generate single-frequency hydrodynamic instability waves, resulting near-field fluctuations far-field acoustics are compared those...

Dual-plane, high-cadence, stereoscopic particle-image velocimetry of a turbulent jet is used to investigate the spatial structure acoustically important wave packets; these are shown have fundamentally different coherence decay and phase speed from energy-containing eddies that dominate pointwise measurements.

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