Wavelike Eddies in a Turbulent Jet

Chan, Y. Y.

doi:10.2514/3.60740

Cited by 31 publications

(16 citation statements)

References 19 publications

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“…An estimate of around 0.52 W is obtained for the azimuthally forced case, which is lower than the phase speed of the axisymmetric vortex rings (0.65 W). The computed phase speeds agrees with experimental measurements of Chan (1977), who showed that the first azimuthal mode had a phase speed of 0.5 W whereas the axisymmetric mode has a phase speed of 0.6 W The separation between consecutive structures in the jet shear layer can be also used to estimate the wavelength or the instability. For azimuthal forcing, a wavelength Aof around 1.1 D was obtained which gives a nontraditional wave number nD/A of around 2.85.…”

Section: Risupporting

confidence: 79%

“…The importance of coherent structures in the transport of momentum and in noise production has been clearly demonstrated in a variety of flow fields (c.g., Ho and Nosseir, 1981;Nosseir and Ho, 1982;Moore, 1977) and has motivated many numerical studies aimed at understanding the dynamics of these structures (e.g., Davis and Moore, 1982;Metcalfe et al, 1987). In free jet flows, the of coherent structures has been studied by artificially exciting the jet at a specified frequency (e.g., Crow and Champagne, 1971;Chan, 1974Chan, , 1977Zaman and Hussain, 1980). This approach suppresses the natural instability of the jet and, thus, allows detailed study of the characteristics of the artificially created coherent structures.…”

Section: L Introductionmentioning

confidence: 99%

“…Also, studies of free jets indicate that the evolution of non-axisymmetric modes is quite important for the breakdown of the farge structures and the transition to turbulence (e.g., Yule, 1978). Experimental study of forced free jets (e.g., Chan, 1977) has shown that in addition to an axisymmetric wave train, a helical wave system with azimuthal wave numbers greater than or equal to I can exist. In the experimental studies of impinging jets, it has been observed that the axisymmetric rings shed by the jet propagate along the ground and eventually breakdown, possibly due to the growth of azimuthal disturbances (e.g., Didden and Ho, 1985;Cerra and Smith, 1980;Wid nail and Tsai, 1977 -I 1.50 1-3.00 -1 1 .…”

Section: L Introductionmentioning

confidence: 99%

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Large-Eddy Simulations of Forced Three-Dimensional Impinging Jets

Menow

Rizk

1996

International Journal of Computational Fluid Dynamics

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Section: Risupporting

confidence: 79%

Section: L Introductionmentioning

confidence: 99%

Section: L Introductionmentioning

confidence: 99%

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Large-Eddy Simulations of Forced Three-Dimensional Impinging Jets

Menow

Rizk

1996

International Journal of Computational Fluid Dynamics

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“…In a jet excited by naturally occurring disturbances, the largescale coherent structures occur over a band of frequencies and over various azimuthal mode numbers. The nature of these structures has often been characterized using correlation functions (Fuchs 1974, Chan 1977, Drubka 1981, Sreenivasan 1984. Application of the modal spectrum representation provides the ability to resolve the coherent, naturally occurring 4i6 axisymmetric and azimuthal modes over a range of frequencies (Rice et al 199o, Raman et al 1991).…”

Section: Introductionmentioning

confidence: 99%

Mode spectra of natural disturbances in a circular jet and the effect of acoustic forcing

Raman

Rice

Reshotko

1994

Experiments in Fluids

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A modal spectrum technique was used to study coherent instability modes (both axisymmetric and azimuthal) triggered by naturally occurring disturbances in a circular jet. This technique was applied to a high Reynolds number (4oo,ooo) jet for both untripped (transitional) and tripped (turbulent) nozzle exit boundary layers, with both cases having a core turbulence level of o.15%. The region up to the end of the potential core was dominated by the axisymmetric mode, with the azimuthal modes dominating further downstream. The growth of the azimuthal modes was observed closer to the nozzle exit for the jet with a transitional boundary layer. Whether for locally parallel flow or slowly diverging flow, even at low levels of acoustic forcing, the inviscid linear theory is seen to be inadequate for predicting the amplitude of the forced mode. In contrast, the energy integral approach reasonably predicts the evolution of the forced mode.

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“…During the past several years a class of jet noise theories has undergone development by several authors including Tarn, U2 Chan, 3 ' 4 Liu, 5 ' 6 and Morris. 7 " 9 These theories are built upon a substantial amount of experimental evidence which has demonstrated that there is an organized structure in turbulent free shear flows.…”

Section: Introductionmentioning

confidence: 99%

Instability process in low Reynolds number supersonic jets

Morrison

McLaughlin

1980

AIAA Journal

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ZL.&fiO. 7 f -?Hot-wire measurements in low Reynolds number axisymmetric perfectly expanded cold jets of Mach number 1.4, 2.1, and 2.5 have been performed. There is a narrow band of unstable frequencies present in the instability of each jet which becomes broader, with more spectral peaks as the Mach number increases. The most dominant spectral component in each jet decreases in Strouhal number with increasing Mach number so that the Helmholtz number (H=fd/aj) remains approximately constant at //=0.4. The instability in each jet is initially in the flapping mode which is a superposition of right-and left-hand helices (n= + 1, -1). Phase speeds of dominant spectral components calculated from frequency and wavelength measurements are between 58% and 70% of the jet exit velocity. No substantial alteration of the instability's structure appears associated with the transition from subsonic to supersonic instability waves (relative to the ambient acoustic velocity). The growth rates decrease strongly with increasing Mach number and are in reasonable agreement with the theories of Tarn and Morris. The saturation and subsequent decay on the instability is coincident with a drastic decrease in the coherence of the instability. Associated research shows that the rapid growth and decay is of fundamental importance in the noise generation process. c D d f H k k l k r M m n PC r Re St t u U x y 7, d Nomenclature = local speed of sound = speed of sound outside jet = wavespeed in the downstream direction diameter of the jet = effective diameter of the jet = frequency = modified Helmholtz number = M-St =fd/ctj = complex wavenumber = imaginary portion of k = real portion of k = Mach number of the jet exit on the centerline -normalized rnass velocity fluctuations -azimuthal mode number = test chamber pressure = radial distance from jet centerline = radial distance from jet centerline where u = aU 0 = Reynolds number = pUd/fji, based on jet exit conditions = Strouhal number =fd/U = local velocity = mean centerline velocity of the jet at the nozzle exit = mean centerline velocity of the jet at a given x location = downstream distance from nozzle exit = vertical distance from jet centerline = horizontal distance from jet centerline = local shear layer thickness Received Sept. 24, 1979. r = period of the coherent structure co = frequency i? =[r-r(0.5)]/5 6 = azimuthal angle = relative phase p = local density ju, = viscosity X -wavelength of fluctuation O = time averaged quantity ( ) r / ms = room mean square of fluctuating quantity

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Wavelike Eddies in a Turbulent Jet

Cited by 31 publications

References 19 publications

Large-Eddy Simulations of Forced Three-Dimensional Impinging Jets

Large-Eddy Simulations of Forced Three-Dimensional Impinging Jets

Mode spectra of natural disturbances in a circular jet and the effect of acoustic forcing

Instability process in low Reynolds number supersonic jets

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