DNS of backward‐facing step flow with fully turbulent inflow

Barri, Mustafa; Khoury, George K. El; Andersson, Helge I.; Pettersen, Bjørnar

doi:10.1002/fld.2176

Cited by 42 publications

(24 citation statements)

References 16 publications

(35 reference statements)

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“…Beyond this threshold, the X r only depends on the ER. In the present paper, and despite the recirculation length increasement with respect to the case studied by Barri et al (2010), the recirculation x 3 /2πh zone remains far enough to be affected by the outflow effects. More information regarding the stream-wise length can be obtained in Section 4.…”

Section: Verification Of the Simulationmentioning

confidence: 54%

“…This simulation time reduction can be attributed to the fact that different time integration techniques are applied. A set of individual quasi-independent flow fields separated by 0.25h/u τ were taken into account by Barri et al (2010), whereas a continuous integration along time is used in the present paper. Apart from that, other factors such as the Re τ could also affect the integration time period.…”

Section: Verification Of the Simulationmentioning

confidence: 99%

“…This author also studied how those structures were related to the X r oscillations. However, few authors carried out research at higher Reynolds numbers and using turbulent inflows, such as Meri & Wengle (2002) and Barri et al (2010). The former studied the effect of 2 nd and 4 th order spatial discretization schemes at Re b = 3300 and a ER = 1.5, while the latter used a Re b = 5600 and ER = 2 by testing its turbulent inflow boundary condition in a configuration with a non-homogeneous stream-wise direction.…”

Section: Introductionmentioning

confidence: 99%

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Direct numerical simulation of backward-facing step flow at and expansion ratio 2

et al. 2019

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Backward-facing step (BFS) constitutes a canonical configuration to study wall-bounded flows subject to massive expansions produced by abrupt changes in geometry. Recirculation flow regions are common in this type of flow, driving the separated flow to its downstream reattachment. Consequently, strong adverse pressure gradients arise through this process, feeding flow instabilities. Therefore, both phenomena are strongly correlated as the recirculation bubble shape defines how the flow is expanded, and how the pressure rises. In an incompressible flow, this shape depends on the Reynolds value and the expansion ratio. The influence of these two variables on the bubble length is widely studied, presenting an asymptotic behaviour when both parameters are beyond a certain threshold. This is the usual operating point of many practical applications, such as in aeronautical and environmental engineering. Several numerical and experimental studies have been carried out regarding this topic. The existing simulations considering cases beyond the above-mentioned threshold have only been achieved through turbulence modelling, whereas direct numerical simulations (DNS) have been performed only at low Reynolds numbers. Hence, despite the great importance of achieving this threshold, there is a lack of reliable numerical data to assess the accuracy of turbulence models. In this context, a DNS of an incompressible flow over a BFS is presented in this paper, considering a friction Reynolds number ($Re_{\unicode[STIX]{x1D70F}}$) of 395 at the inflow and an expansion ratio 2. Finally, the elongation of the Kelvin–Helmholtz instabilities along the shear layer is also studied.

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Section: Verification Of the Simulationmentioning

confidence: 54%

Section: Verification Of the Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Direct numerical simulation of backward-facing step flow at and expansion ratio 2

et al. 2019

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“…x = 3.0η, it is unlikely that the error is very large. Mesh sizes of around 5η are usually reckoned to provide adequate resolution (Kim, Moin & Moser 1987;Barri et al 2010). One can also estimate the minimum value of the Kolmogorov time scale, τ = (Re ) −1/2 = 0.17 using the = 0.0085 value.…”

Section: Deductions From Spectral Datamentioning

confidence: 99%

A turbulent patch arising from a breaking internal wave

2011

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Results of direct numerical simulations of the development of a breaking internal gravity wave are presented. The wave was forced by the imposition of an appropriate bottom boundary shape (a two-dimensional cosine hill) within a density-stratified domain having a uniform upstream velocity and density gradient. The focus is on turbulence generation and maintenance within the turbulent patch generated by the wave breaking. Pathlines, density contours, temporal and spatial spectra, and second moments of the velocity and density fluctuations and turbulent kinetic energy balance terms obtained from the data averaged over the span in the mixed zone are all used in the analysis of the flow. Typical Reynolds numbers, based on the vertical scale of the breaking region and the upstream velocity, were around 6000 and the fully resolved computations yielded sufficient resolution to capture the fine-scale transition processes as well as the subsequent fully developed turbulence. It is shown that globally, within the turbulent patch, there is an approximate balance in the production, dissipation and transport processes for turbulent kinetic energy, so that the patch remains quasi-steady over a significant time. Although it is far from being axially homogeneous, with turbulence generation occurring largely near the upstream bottom part of the patch where the mean velocity shear is particularly large, it has features not dissimilar to those of a classical turbulent wake.

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“…This is explained fully in Yakovenko et al (2011). Note that the Kolmogorov scale η was estimated using the maximum value of the dissipation in the turbulent patch, obtained by time and spatial averaging of the usual relation containing the fluctuating strain tensor, and that mesh sizes of 5η are usually reckoned to provide adequate resolution (Kim, Moin & Moser 1987;Barri et al 2010). The run was performed with Re = Uh/ν = 4000, Pr = 1 and F h = 0.6 and used a (nondimensional) time step of t = 0.0005, satisfying the Courant number restrictions arising from the advection and 'drag' terms.…”

Section: Methodsmentioning

confidence: 99%

Transition through Rayleigh–Taylor instabilities in a breaking internal lee wave

2014

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Results of direct numerical simulations of the transitional processes that characterise the evolution of a breaking internal gravity wave to a fully developed and essentially steady turbulent patch are presented. The stationary lee wave was forced by the imposition of an appropriate bottom boundary shape within a density-stratified domain having a uniform upstream velocity and density gradient, and with the ratio of momentum to thermal (or other) diffusivity defined by Pr = 1. An earlier paper considered the eventual, fully developed turbulent patch arising after the breaking process is complete (Yakovenko et al., J. Fluid Mech., vol. 677, 2011, pp. 103-133); the focus in this paper is on the instabilities in the breaking process itself. The flow is analysed using streamlines, density contours and temporal and spatial spectra, as well as second moments of the velocity and density fluctuations, for a Reynolds number of 4000 based on the height of the bottom topography and the upstream velocity. The computations (on a grid using in excess of 10 9 mesh points) yielded sufficient resolution to capture the fine-scale transition processes as well as the subsequent fully developed turbulence discussed earlier. It is shown that the major instability is of Rayleigh-Taylor type (RTI) with a resulting mixing region depth growing in a manner consistent with more classical RTI studies, despite the much more complicated environment. The resolution was sufficient to capture secondary Kelvin-Helmholtz-type instabilities on the developing RTI structures. Overall evolution towards the fully turbulent state characterised by a significant region of − 5 3 subrange in both velocity and density spectra is very rapid. It is much faster than the long time scale characterising the subsequent evolution of the turbulent patch; this latter time scale is sufficiently large that the turbulent patch can itself be viewed as essentially steady.

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DNS of backward‐facing step flow with fully turbulent inflow

Cited by 42 publications

References 16 publications

Direct numerical simulation of backward-facing step flow at and expansion ratio 2

Direct numerical simulation of backward-facing step flow at and expansion ratio 2

A turbulent patch arising from a breaking internal wave

Transition through Rayleigh–Taylor instabilities in a breaking internal lee wave

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