Organised large structure in the post-transition mixing layer. Part 2. Large-eddy simulation

McMullan, W. A.; Gao, Shian; Coats, C.M.

doi:10.1017/jfm.2014.660

Cited by 26 publications

(80 citation statements)

References 55 publications

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“…24 Whilst these studies were limited to the pre-transition region, more recent research has shown that simulation of initially laminar mixing layers with pseudorandom inflow disturbances leads to post-transition large-scale coherent structures which grow continuously and linearly throughout their lifetimes. 23 Flow visualisation of the high Reynolds number simulated flow shows that streamwise vorticity develops in the mixing layer, and that the streamwise vorticity persists far into the turbulent region. 22,23,26,27 Evidence for the presence of statistically stationary streamwise vorticity, however, appears to be lacking in all of these spatially-developing mixing layer computations.…”

Section: Introductionmentioning

confidence: 95%

“…23 Flow visualisation of the high Reynolds number simulated flow shows that streamwise vorticity develops in the mixing layer, and that the streamwise vorticity persists far into the turbulent region. 22,23,26,27 Evidence for the presence of statistically stationary streamwise vorticity, however, appears to be lacking in all of these spatially-developing mixing layer computations.…”

Section: Introductionmentioning

confidence: 95%

“…Direct Numerical Simulation (DNS) of the high-Reynolds number, spatially-developing mixing layer is now within reach, 21,22 and Large Eddy Simulation (LES) has also been shown to produce accurate mixing layer data on suitably refined meshes. 23 The most challenging aspect of numerical simulation is the specification of accurate time-dependent inflow conditions. To the authors' knowledge, there exists no experimental data for mixing layers where the mean and fluctuating parts of the flow conditions at the splitter plate trailing edge are fully documented.…”

Section: Introductionmentioning

confidence: 99%

“…Initially-laminar spatial mixing layer simulation inflow conditions are typically produced from a base mean velocity profile onto which pseudo-random white noise fluctuations are superimposed at each time step. 21,23,24,25 In the pre-transition region the nature of the imposed disturbances influences the nature of the laminar vortices. Three-dimensional random disturbances result in structures which undergo localised pairings, whilst highly two-dimensional random disturbances produce concentrated streamwise vortices between the primary rollers.…”

Section: Introductionmentioning

confidence: 99%

“…This type of fluctuation environment is commonly used in DNS database simulations, 21,32 and in Large Eddy Simulations of the mixing layer. 23,24 A further simulation is performed where the disturbance environment is generated using a recycling and rescaling method. 30 The origin and evolution of the streamwise vorticity in both simulations will be analysed and compared to relevant experimental data where appropriate.…”

Section: Introductionmentioning

confidence: 99%

See 4 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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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: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 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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Mixing and combustion at low heat release in large eddy simulations of a reacting shear layer

Huang

McMullan

2021

Theor. Comput. Fluid Dyn.

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In this paper, the mixing and combustion at low-heat release in a turbulent mixing layer are studied numerically using large eddy simulation. The primary aim of this paper is to successfully replicate the flow physics observed in experiments of low-heat release reacting mixing layers, where a duty cycle of hot structures and cool braid regions was observed. The nature of the imposed inflow condition shows a dramatic influence on the mechanisms governing entrainment, and mixing, in the shear layer. An inflow condition perturbed by Gaussian white noise produces a shear layer which entrains fluid through a nibbling mechanism, which has a marching scalar probability density function where the most probable scalar value varies across the layer, and where the mean-temperature rise is substantially over-predicted. A more sophisticated inflow condition produced by a recycling and rescaling method results in a shear layer which entrains fluid through an engulfment mechanism, which has a non-marching scalar probability density function where a preferred scalar concentration is present across the thickness of the layer, and where the mean-temperature rise is predicted to a good degree of accuracy. The latter simulation type replicates all of the flow physics observed in the experiment. Extensive testing of subgrid-scale models, and simple combustion models, shows that the WALE model coupled with the Steady Laminar Flamelet model produces reliable predictions of mixing layer diffusion flames undergoing with fast chemistry.

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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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Organised large structure in the post-transition mixing layer. Part 2. Large-eddy simulation

Cited by 26 publications

References 55 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

Mixing and combustion at low heat release in large eddy simulations of a reacting shear layer

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

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