Organized large structure in the post-transition mixing layer. Part 1. Experimental evidence

D’Ovidio, A.; Coats, C.M.

doi:10.1017/jfm.2013.553

Cited by 35 publications

(20 citation statements)

References 57 publications

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“…Each of the structures grows continuously and linearly throughout its lifetime, with the diameter of the structures defining the self-similar growth of the mixing layer as a whole. This pattern of continuous linear growth has been reported in experiments, 55 and numerical simulations where the inflow conditions were of the same type as those of Case WN. 23 The continuous linear growth of the structures in Case WN suggests that interactions between the structures has little impact on the growth of the layer.…”

Section: Post-transition Vortical Structure Growth and Interactionsupporting

confidence: 80%

“…We postulate that the three-dimensional coherent structures present in Case WN are of the same form as those observed in the uniform density experiments of D'Ovidio & Coats. 55 It is interesting to note that the uniform density visual thickness growth rates reported by Brown & Roshko 1 are approximately 13% higher than those observed by D'Ovidio & Coats 55 for the uniform density flow. This di↵erence in growth rate is similar to that reported between Cases RRM and WN, where a mixing layer containing quasitwo-dimensional post-transition structures has a 15% higher growth rate than one which contains inherently three-dimensional coherent structures.…”

Section: Discussionmentioning

confidence: 71%

“…52 An alternative interpretation of the evolution of the turbulent mixing layer, however, has also been presented. 55 In these experiments the post-transition vortical structures in the uniform density mixing layer grew continuously and linearly throughout their lifetimes, with structure interactions serving only to reduce the number density of the structures and to facilitate the continuous linear growth. This view of the mixing layer is incompatible with a two-dimensional interpretation of the flow, as there is no obvious mechanism by which the structures can grow continuously if the spanwise vorticity is condensed into (quasi-)two-dimensional clumps.…”

Section: Discussionmentioning

confidence: 94%

“…The diameter of each structure is calculated from the vertical distance between the polar points. This method has been used in previous experimental 55 and numerical 23 investigations into the turbulent mixing layer.…”

Section: Post-transition Vortical Structure Growth and Interactionmentioning

confidence: 99%

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Initial condition effects on large scale structure in numerical simulations of plane mixing layers

McMullan

Garrett

2016

Physics of Fluids

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In this paper Large Eddy Simulations are performed on the spatially developing plane turbulent mixing layer. The simulated mixing layers originate from initially laminar conditions. The focus of this research is on the e↵ect of the nature of the imposed fluctuations on the large-scale spanwise and streamwise structures in the flow. Two simulations are performed; one with low-level three-dimensional inflow fluctuations obtained from pseudo-random numbers, the other with physically-correlated fluctuations of the same magnitude obtained from an inflow generation technique. Where white-noise fluctuations provide the inflow disturbances, no spatially stationary streamwise vortex structure is observed, and the large-scale spanwise turbulent vortical structures grow continuously and linearly. These structures are observed to have a three-dimensional internal geometry with branches and dislocations. Where physically-correlated provide the inflow disturbances a 'streaky' streamwise structure that is spatially stationary is observed, with the large-scale turbulent vortical structures growing with the square-root of time. These large-scale structures are quasi-two-dimensional, on top of which the secondary structure rides. The simulation results are discussed in the context of the varying interpretations of mixing layer growth that have been postulated. Recommendations are made concerning the data required from experiments in order to produce accurate numerical simulation recreations of real flows.

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Section: Post-transition Vortical Structure Growth and Interactionsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 94%

Section: Post-transition Vortical Structure Growth and Interactionmentioning

confidence: 99%

See 2 more Smart Citations

Initial condition effects on large scale structure in numerical simulations of plane mixing layers

McMullan

Garrett

2016

Physics of Fluids

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“…Analysis of flow visualisations of high Reynolds number mixing layer suggests that a significant proportion of the growth of the mixing layer occurs between interactions (Hernan and Jimenez 1982). Recent experimental work by D 'Ovidio and Coats (2013) suggests that both mechanisms exist in the mixing layer; in the pre-transition region the mixing layer grows through pairing-type interactions, whilst in the post-transition region the self-similar growth of the mixing layer is accounted for by the continuous linear growth of the coherent structures (D'Ovidio and Coats 2013). The distinction between the laminar and turbulent regions of the flow is marked by the mixing transition (Konrad 1976).…”

Section: Introductionmentioning

confidence: 99%

Spanwise domain effects on the evolution of the plane turbulent mixing layer

McMullan

2015

International Journal of Computational Fluid Dynamics

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Large Eddy Simulation is used to simulate a series of plane mixing layers. The influence of the spanwise domain on the development of the mixing layer, and the evolution of the coherent structures are considered. The mixing layers originate from laminar conditions, and an idealised inflow condition is found to produce accurate flow predictions when the spanwise computational domain extent is sufficient to avoid confinement effects. Spanwise domain confinement of the flow occurs when the ratio of spanwise domain extent to local momentum thickness reaches a value of ten. Flow confinement results in changes to both the growth mechanism of the turbulent coherent structures, and the nature of the interactions that occur between them. The results demonstrate that simulations of the two-dimensional mixing layer flow requires a three-dimensional computational domain in order that the flow will evolve in a manner that is free from restraints imposed by the spanwise domain.

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Growth of organized flow coherent motions within a single-stream shear layer: 4D-PTV measurements

Gautam,

Livescu,

Mejia-Alvarez

2024

Exp Fluids

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This study investigates the evolution of a single-stream shear layer (SSSL) originating from a wall boundary layer past a backward-facing step. Utilizing a time-resolved 3D-Particle Tracking Velocimetry (4D-PTV) technique, we track the trajectories of fluorescent particles to gain insight into the flow characteristics of the SSSL. A compact water tunnel facility ($$\textrm{Re}_\tau =1\,240$$ Re τ = 1 240 ) is fabricated to obtain an SSSL with a perpendicular slow entrainment stream past the separation edge. A hybrid interpolation approach that combines ensemble binning and Gaussian weighting is implemented to derive minimally filtered mean and instantaneous lower- and higher-order flow field parameters. Spanwise-dominant coherent motion accompanied by finer flow scales is observed to grow due to flow entrainment through “nibbling” actions of small-scale vortices, “engulfing” by large-scale vortices, and vortex pairing events. Furthermore, the non-zero-speed stream edge grows relatively faster than the zero-speed stream edge, showing a strong asymmetry in mixing composition across a mixing layer. The SSSL reaches self-similarity at a streamwise distance of $$\approx 55\,\theta _{0}$$ ≈ 55 θ 0 , where $$\theta _0$$ θ 0 is the initial momentum thickness from the separation edge, i.e., considerably shorter than reported in previous studies. A literature comparison of growth rate parameters raises intriguing questions regarding a potential inclusive growth scaling unifying the free shear layers. A turbulent kinetic energy (TKE) budget analysis reveals a negative production region immediately downstream of the separation edge attributed to a large positive streamwise gradient of streamwise velocity. In the self-similar region, the phase-averaged flow mapping demonstrates a larger concentration of turbulence production rate around the outer edges of spanwise vortices, specifically at the intersection of braids and vortices. Furthermore, a spatial separation exists in the regions of peak production and dissipation rates within the vortex core region favoring dissipation. The braids exhibit a larger concentration of turbulence diffusion rates, indicating their function as a conduit for exchanging turbulence between neighboring coherent motions.

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Organized large structure in the post-transition mixing layer. Part 1. Experimental evidence

Cited by 35 publications

References 57 publications

Initial condition effects on large scale structure in numerical simulations of plane mixing layers

Initial condition effects on large scale structure in numerical simulations of plane mixing layers

Spanwise domain effects on the evolution of the plane turbulent mixing layer

Growth of organized flow coherent motions within a single-stream shear layer: 4D-PTV measurements

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