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

Garrett

2016

Physics of Fluids

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.

Section: B Validationsupporting

confidence: 65%

Section: Post-transition Vortical Structuresmentioning

confidence: 99%

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

Garrett

2016

Physics of Fluids

“…This type of secondary structure has been observed in other mixing layer simulation originating from initially-laminar conditions with a white noise disturbance environment. 27,34 Further downstream (Figures 6b-6c) a single row of 'mushroom-shaped' eruptions is visible along the span of the braid region, indicating the presence of a row of streamwise vortices. In Case WNH ( Figure 7) a similar cross-plane scalar evolution is observed, although the wavelength of the secondary instability at x = 0.07m is qualitatively much shorter than that of Case WNL.…”

Section: B Flow Visualisationmentioning

confidence: 99%

Resolved Scalar Mixing in Large Eddy Simulations of a Low Reynolds Number Plane Mixing Layer

Hug

22nd AIAA Computational Fluid Dynamics Conference

2015

In this paper we present Large Eddy Simulations of a low Reynolds number plane mixing layer. The purpose of the research is to assess the effect of inflow conditions on the scalar mixing in the flow. A high-resolution grid is used to study a pre-transition mixing layer originating from initially laminar conditions. Both pseudo-random white noise and physically-correlated fluctuations produced by an inflow generation technique provide the background fluctuations for the simulations. It is found that the scalar statistics are largely spanwise invariant when pseudo-random fluctuations are employed, whilst large spanwise variations in the scalar statistics are observed when physically-correlated fluctuations provide the background disturbances. The large fluctuations are attributed to the presence of organised streamwise vortices in the mixing layer. The implications of this research in terms of the documentation of experimental initial conditions is discussed.

“…The spanwise domain extent is chosen such that the developing mixing layer will be free from any spanwise confinement effects. 37 The spanwise boundaries are periodic in nature. The domain is discretised into 768 × 256 × 256 cells in each direction respectively.…”

Section: Simulation Set-upmentioning

confidence: 99%

The Effect of Initial Conditions on Streamwise Vortices in the Plane Turbulent Mixing Layer

22nd AIAA Computational Fluid Dynamics Conference

Garrett

2015

In this research we investigate the effect of inflow conditions on the streamwise vortices that exist in the plane turbulent mixing layer. Both initially-laminar and initially-turbulent mixing layers are considered here. The effect of the imposed fluctuations is assessed in the initially-laminar mixing layer simulations through the use of a white noise disturbance environment, and a physically-correlated fluctuation environment produced by an inflow generation method. The initially-turbulent mixing layer has its inflow condition produced by the inflow generation method. Each simulation produces good statistical agreement with the experimental data. The initially-laminar simulation with correlated fluctuations predicts the presence of statistically stationary streamwise vortices, whilst the other two simulations do not.