Tone excited jets, part III: Flow measurements

Lepicovsky, J.; Ahuja, K. K.; Burrin, R. H.

doi:10.1016/s0022-460x(85)80104-8

Cited by 33 publications

(13 citation statements)

References 6 publications

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“…Excitation can result in an amplification of instabilities in the mixing layer and increase the strength of the vortical structures (Crow & Champagne 1971;Moore 1977;Hussain & Zaman 1980). The potential core is also shortened because of the perturbation and is a sign of greater mixing (Lepicovsky, Ahuja & Burrin 1985).…”

Section: Background Literaturementioning

confidence: 99%

Simulation of the blooming phenomenon in forced circular jets

2015

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The bifurcation and the blooming of jets have been numerically investigated at moderate Reynolds numbers. The study is motivated by a review article of Reynolds et al. (Annu. Rev. Fluid Mech., vol. 35, 2003, pp. 295-315) in which flow visualization images of jet blooming have been discussed, when the flow is subjected to inflow perturbations. Dual-mode perturbation, a combination of axisymmetric and helical excitations, has been used at the inflow plane to control the jet structures. In addition to the excitation frequency ratio, the effects of small-scale perturbation, excitation amplitude and initial momentum thickness have been examined. Results obtained at a Reynolds number of 2000 show that the number of branches formed in the blooming jet is strongly dependent on the excitation frequency ratio. For frequency ratios of 2, 2.5, 2.25, 2.4 and 2.22, the number of branches seen is 2, 5, 9, 12 and 20 respectively. In a blooming jet, the offset angle lies in the range 140 • -180 • . An equal number of branches is seen in the time-averaged flow field as well. The range of excitation frequency of the axisymmetric mode of perturbation is found to be 0.45 < St D < 0.525, with an excitation frequency ratio range of 2 < R f < 2.6, for which blooming jets are formed. The role of inlet shear layer thickness is less important as far as the blooming jet is concerned, while increasing excitation amplitude increases entrainment. Time-averaged data show that the blooming patterns persist in time, showing a substantial increase in spreading and entrainment.

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Section: Background Literaturementioning

confidence: 99%

Simulation of the blooming phenomenon in forced circular jets

2015

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“…There have been a few experiments which used active control in supersonic jets (e.g. Troutt & McLaughlin 1982;Morrison 1983;Ahuja and Blakney 1985;Ahuja and Whiffen 1985;Lepicovsky et al 1985a;Lepicovsky, Ahuja & Burrin 1985b). The most relevant conclusion of these works is that both subsonic and supersonic jets support the existence of large turbulence structures; even in the presence of shocks.…”

Section: Flow Controlmentioning

confidence: 99%

A study of Mach wave radiation using active control

2011

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Mach wave radiation is one of the better understood sources of jet noise. However, the exact conditions of its onset are difficult to determine and the literature to date typically explores Mach wave radiation well above its onset conditions. In order to determine the conditions for the onset of Mach wave radiation and to explore its behaviour during onset and beyond, three ideally expanded jets with Mach numbers M j = 0.9, 1.3 and 1.65 and stagnation temperature ratios ranging over T o /T ∞ = 1.0-2.5 (acoustic Mach number 0.83-2.10) were used. Data are collected using a far-field microphone array, schlieren imaging and streamwise two-component particle image velocimetry. Using arc filament plasma actuators to force the jet provides an unprecedented tool for detailed examination of Mach wave radiation. The response of the jet to various forcing parameters (combinations of one azimuthal mode m = 0, 1 and 3 and one Strouhal number St DF = 0.09-3.0) is explored. Phaseaveraged schlieren images clearly show the onset and evolution of Mach wave radiation in response to both changes in the jet operating conditions and forcing parameters. It is observed that Mach wave radiation is initiated as a coalescing of the near-field hydrodynamic pressure fluctuations in the immediate vicinity of the large-scale structures. As the jet exit velocity increases, the hydrodynamic pressure fluctuations coalesce, first into a curved wavefront, then flatten into the conical wavefronts commonly associated with Mach wave radiation. The results show that the largest and most coherent structures (e.g. forcing with m = 0 and St DF ∼ 0.3) produce the strongest Mach wave radiation. Conversely, Mach wave radiation is weakest when the structures are the least coherent (e.g. forcing with m = 3 and St DF > 1.5).

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“…On the other hand, the responses of the coaxial jet upon acoustic excitation were studied by Lepicovsky et al (1985), Tang and Ko (1993; and Wicker and Eaton (1994). also observed the flow structure in the initial region of an excited coaxial jet with the mean velocity ratio of 0.3.…”

Section: Introductionmentioning

confidence: 97%

Flow visualization of vortex structure of an excited coaxial jet

Kiwata

Okajima

2001

J Vis

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This paper describes the results of experimental and numerical studies concerning the nearfield vortical structure and dynamics of a coaxial jet. The effect of excitation of annular and circular jets on the vortical structure in the inner and outer shear-layers was studied. The flow visualization and the measurements of mean and fluctuating velocities, by a hot-film probe and the particle image velocimetry (PIV) technique, were carried out in an open water tank. The results of flow visualization and numerical simulation are in good agreement. With the excitation of a half of the initial vortex frequency, it is found that the vortex-pairing event is promoted by the forced excitation and it results in the rapid expansion of the jet width and the increase of velocity fluctuation and the entrainment rate. For the velocity ratio near unity, the dominant peak frequency coincides with the initial vortex frequency, Le., the lip wake vortex frequency, independent of the forced excitation frequency.

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Tone excited jets, part III: Flow measurements

Cited by 33 publications

References 6 publications

Simulation of the blooming phenomenon in forced circular jets

Simulation of the blooming phenomenon in forced circular jets

A study of Mach wave radiation using active control

Flow visualization of vortex structure of an excited coaxial jet

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