On the effect of initial conditions on the two dimensional turbulent mixing layer

Oster, D.; Wygnanski, I.; Dziomba, B.; Fiedler, H. E.

doi:10.1007/3-540-08765-6_5

Cited by 52 publications

(38 citation statements)

References 6 publications

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“…would also like to thank Professor I. J. Wygnanski for a short discussion in which he brought to our attention the results on the mixing-layer growth by Batt (1975 Note added in proof. Recent experimental investigations (Oster 1976) corroborate the long-term coherence of the shear-layer large structures observed in this experiment. More direct evidence supporting the presence of a feedback mechanism, hypothesized in this paper, was found in the form of a frequency of the order of LIU, ( L = length of shear layer) in the spectrum of the velocity fluctuations at all valzces of the streamwise co-ordinate.…”

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confidence: 86%

The mixing layer at high Reynolds number: large-structure dynamics and entrainment

1976

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A turbulent mixing layer in a water channel was observed at Reynolds numbers up to 3 x los. Flow visualization with dyes revealed (once more) large coherent structures and showed their role in the entrainment process; observation of the reaction of a base and an acid indicator injected on the two sides of the layer, respectively, gave some indication of where molecular mixing occurs. Autocorrelations of streamwise velocity fluctuations, using a laser-Doppler velocimeter (LDV) revealed a fundamental periodicity associated with the large structures. The surprisingly long correlation times suggest time scales much longer than had been supposed; it is argued that the mixing-layer dynamics at any point are coupled to the large structure further downstream, and some possible consequences regarding the effects of initial conditions and of the influence of apparatus geometry are discussed.

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confidence: 86%

The mixing layer at high Reynolds number: large-structure dynamics and entrainment

1976

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“…In the former experiment, the boundary layer was laminar, while in the latter it was turbulent. The association of this increase in shear-layer growth with the state of the splitter-plate boundary-layer (initial) condition was confirmed by the work of Batt (1975), and Oster, Wygnanski & Fiedler (1976). Interestingly, for non-zero velocity ratios, i.e.…”

Section: Introductionmentioning

confidence: 71%

Turbulent shear-layer mixing at high Reynolds numbers: effects of inflow conditions

1998

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We report on the results from a set of incompressible, shear-layer flow experiments, at high Reynolds number (Re δ ≡ ρ ∆U δ T (x)/µ 2 × 10 5 ), in which the inflow conditions of shear-layer formation were varied (δ T is the temperature-rise thickness for chemically-reacting shear layers). Both inert and chemically-reacting flows were investigated, the latter employing the (H 2 +NO)/F 2 chemical system in the kineticallyfast regime to measure molecular mixing. Inflow conditions were varied by perturbing each, or both, boundary layers on the splitter plate separating the two freestream flows, upstream of shear-layer formation. The results of the chemically-reacting 'flip experiments' reveal that seemingly small changes in inflow conditions can have a significant influence not only on the large-scale structure and shear-layer growth rate, as had been documented previously, but also on molecular mixing and chemicalproduct formation, far downstream of the inflow region.

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“…At first, the research was limited to a statistical description of the flow, but since 1970s, it focused on conditional statistics and on coherent structures (Wygnanski & Fiedler 1970, Brown & Roshko 1974, Winant & Browand 1974Browand & Weidman 1976;Wygnanski et al 1979;Hussain 1983 etc.). When it was realized that the coherent structures play a central role in the evolution of the mixing layer, artificial excitation was soon to follow (Oster et al 1978;Oster & Wygnanski 1982;Ho & Huang 1982;Gaster et al 1985;Fiedler & Mensing 1985). Fiedler et al (1981), Oster et al (1982) and Monkewitz and Huerre (1982) used the parallel, linear stability analysis to predict the most amplified frequencies and the amplification rates of the large eddies in the externally excited turbulent mixing layer while others used modeling and numerical simulation to obtain similar results (Patnaik et al 1976;Acton 1976;Ashurst 1979;Riley & Metcalfe 1980, Corcos & Sherman 1984, Inoue & Leonard 1987Inoue 1989).…”

Section: Introductionmentioning

confidence: 99%

The response of a mixing layer formed between parallel streams to a concomitant excitation at two frequencies

Zhou

Wygnanski

2001

J. Fluid Mech.

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1Simultaneous excitation of a turbulent mixing layer by two frequencies, a fundamental and a subharmonic, was investigated experimentally. Plane perturbations were introduced to the flow at its origin by a small oscillating flap. The results describe two experiments that differ only in the amplitudes of the imposed perturbations and both are compared to the data acquired while the mixing layer was forced at a single frequency.Conventional statistical quantities such as: mean velocity profiles, widths of the flow, turbulent intensities, spectra, phase-locked velocity and vorticity fields, as well as streak-lines were computed. The rate of spread of the flow under concomitant excitation at the two frequencies was much greater than under a single frequency although it remained dominated by two-dimensional eddies. The Reynolds stresses and turbulence production are associated with the deformation and orientation of the large coherent vortices. When the major axis of the coherent vortices starts leaning forward on the high velocity side of the flow, the production of turbulent energy changes sign (i.e. becomes negative) and it results in thinning the flow in the direction of streaming. It also indicates that energy is extracted from the turbulence to the mean motion Resonance phenomena play an important role in the evolution of the flow. A vorticity budget showed that the change in mean vorticity was mainly caused by the nonlinear interaction between coherent voracities. Nevertheless the locally dominant frequency scales the mean growth rate, the inclination and distortion of the mean velocity profiles as well as the phaselocked vorticity contours. 14, SIMItCT TtAMSSimultaneous excitation of a turbulent mixing layer by two frequencies, a fundamental and a subharmonic, was investigated experimentally. Plane perturbations were introduced to the flow at its origin by a small oscillating flap. The results describe two experiments that differ only in the amplitudes of the imposed perturbations and both are compared to the data acquired while the mixing layer was forced at a single frequency.Conventional statistical quantities such as: mean velocity profiles, widths of the flow, turbulent intensities, spectra, phase-locked velocity and voracity fields, as well as streak-lines were computed. The rate of spread of the flow under concomitant excitation at the two frequencies was much greater than under a single frequency although it remained dominated by two-dimensional eddies. The Reynolds stresses and turbulence production are associated with the deformation and orientation of the large coherent vortices. When the major axis of the coherent vortices starts leaning forward on the high velocity side of the flow, the production of turbulent energy changes sign (i.e. becomes negative) and it results in thinning the flow in the direction of streaming. It also indicates that energy is extracted from the turbulence to the mean motion. Resonance phenomena play an important role in the evolution of the flow. A vorticity bu...

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On the effect of initial conditions on the two dimensional turbulent mixing layer

Cited by 52 publications

References 6 publications

The mixing layer at high Reynolds number: large-structure dynamics and entrainment

The mixing layer at high Reynolds number: large-structure dynamics and entrainment

Turbulent shear-layer mixing at high Reynolds numbers: effects of inflow conditions

The response of a mixing layer formed between parallel streams to a concomitant excitation at two frequencies

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