Aeroacoustics of hot jets

Viswanathan, K.

doi:10.1017/s0022112004000151

Cited by 293 publications

(194 citation statements)

References 19 publications

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“…The decomposed field is found to follow the model spectrum in the pertinent range of acoustic frequencies and indicates a peak at approximately St ∼ 0.2. This is qualitatively consistent with far-field experimental supersonic jet data at similar Mach numbers (Seiner et al 1992;Viswanathan 2004;Tam et al 2008). A similar narrow-band character has also been observed in the near field of near-sonic jet LES .…”

Section: Properties Of the Decomposed Fieldssupporting

confidence: 89%

Acoustic, hydrodynamic and thermal modes in a supersonic cold jet

Nair

Gaitonde

2016

J. Fluid Mech.

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Large-eddy simulation data for a Mach 1.3 round jet are decomposed into acoustic, hydrodynamic and thermal components using Doak's momentum potential theory. The decomposed fields are then analysed to examine the properties of each mode and their dynamics based on the transport equation for the total fluctuating enthalpy. The solenoidal fluctuations highlight hydrodynamic components of the jet and capture the shear layer growth and breakdown process. The acoustic mode exhibits a jittering coherent wavepacket structure in the turbulent region and consequent highly directional downstream radiation. The expected radial decay rates, r for acoustic, are recovered and closely follow the universal radiation spectra in the sideline and downstream directions. The scalogram of the acoustic mode in the near-acoustic-field region is consistent with that of the pressure perturbation signal in the acoustic-frequency range, but effectively removes the hydrodynamic and thermal content. The time-resolved and mean behaviour of terms in the total fluctuating enthalpy equation is analysed in detail. A large-scale intermittent event in the near-acoustic field is shown to be associated with an intrusion of vortices from the shear layer into the core of the jet. Acoustic sources are created when the resulting negative fluctuations in the solenoidal component interact with positive fluctuations in the Coriolis acceleration term. The latter are associated with regions of high vorticity on the inner side of the shear layer. In contrast, sinks result from the interaction of solenoidal momentum fluctuations with positive entropy gradients along entrainment streaks.

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Section: Properties Of the Decomposed Fieldssupporting

confidence: 89%

Acoustic, hydrodynamic and thermal modes in a supersonic cold jet

Nair

Gaitonde

2016

J. Fluid Mech.

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“…If the data confirms to previous evidence [32,37] in which the above suggestion found support, then the measured spectra of the current subsonic jet should fit Tam's FSS and LSS. This is examined by comparing the measured spectra to the LSS and FSS spectra of Tam as shown in Fig.…”

Section: Acoustic Far Field Resultssupporting

confidence: 84%

“…Tam & Burton [31], Tam et al [32] and later on Viswanathan [37] proposed a mechanism by which an acoustic wave may be radiated in a subsonic jet with features similar to Mach wave radiation. The proposed mechanism involves recognising the importance of amplitude modulation of instability waves.…”

Section: Acoustic Far Field Resultsmentioning

confidence: 99%

Experiments on the Flow Field and Acoustic Properties of a Mach number 0·75 Turbulent Air Jet at a Low Reynolds Number

Slot

Moore

Delfos

et al. 2009

Flow Turbulence Combust

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In this paper we present the experimental results of a detailed investigation of the flow and acoustic properties of a turbulent jet with Mach number 0·75 and Reynolds number 3·5 10 3 . We describe the methods and experimental procedures followed during the measurements, and subsequently present the flow field and acoustic field. The experiment presented here is designed to provide accurate and reliable data for validation of Direct Numerical Simulations of the same flow. Mean Mach number surveys provide detailed information on the centreline mean Mach number distribution, radial development of the mean Mach number and the evolution of the jet mixing layer thickness both downstream and in the early stages of jet development. Exit conditions are documented by measuring the mean Mach number profile immediately above the nozzle exit. The fluctuating flow field is characterised by means of a hot-wire, which produced radial profiles of axial turbulence at several stations along the jet axis and the development of flow fluctuations through the jet mixing layer. The axial growth rate of the jet instabilities are determined as function of Strouhal number, and the axial development of several spectral components is documented. The directivity of the overall sound pressure level and several spectral components were investigated. The spectral content of the acoustic far field is shown to be compatible with findings of hot-wire experiments in the mixing layer of the jet. In addition, the measured acoustic spectra agree with Tam's large-scale similarity and fine-scale similarity spectra (Tam et al., AIAA Pap 96, 1996).

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“…The effect of temperature on jet noise has been widely investigated experimentally (Tanna, 1977;Tanna et al, 1975;Viswanathan, 2004). It has been observed that, for a fixed acoustic Mach number M a = U j /c 0 , where c 0 is the sound velocity at ambient temperature, the radiated noise directly depends on the jet temperature.…”

Section: Temperature Effectmentioning

confidence: 99%