DNS of an Oscillating Shear Layer Between Two Parallel Couette Flows
01 Jan 2021-pp 241-246
TL;DR: In this article, a nonplanar mixing layer observed between parallel Couette flows by Narasimhamurthy et al. is considered, and simulations are run in order to determine the critical Reynolds number at which the interface between the co-flowing laminar and non-laminar flow becomes unstable exhibiting a meandering motion.
Abstract: A non-planar mixing layer observed between parallel Couette flows by Narasimhamurthy et al. (Phys Rev E 85:036,302, 2012) is considered. Direct numerical simulation is chosen, and simulations are run in order to determine the critical Reynolds number at which the interface between the co-flowing laminar and non-laminar flow becomes unstable exhibiting a meandering motion. The necessary conditions required to trigger the shear-layer instability were also discussed. Different combinations of Reynolds numbers are chosen keeping the Reynolds number ratio between the laminar and non-laminar flows as constant. Preliminary results indicate that the onset of instability occurs, and a meandering motion is observed at the interface when Reynolds number for the non-laminar flow corresponds to 650.
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TL;DR: In this paper , the authors make a detailed analysis of co-flowing plane Couette flows and study the variation of flow quantities from the turbulent to non-turbulent region.
Abstract: The current article aims to make a detailed analysis of co-flowing plane Couette flows. Particularly, the variation of flow quantities from the turbulent to non-turbulent region is studied. While the enstrophy exhibits a sharp jump, the other quantities (e.g., mean velocity, Reynolds normal stress, and kinetic energy) show a continuous variation across the interface. The budget analysis of Reynolds normal stresses reveal that different terms play their role in turbulence transportation, depending on the Reynolds normal stress under study. The terms production, diffusion, and redistribution play an important role in streamwise Reynolds stress (u'u'). In the spanwise Reynolds stress (v'v'), the diffusion terms play a significant role. In the wall-normal Reynolds stress (w'w') only the redistribution term is significant. The influence of one flow over other in the co-flow state was observed through the additional mean velocity and Reynolds normal stress found in the system compared to a standard plane Couette flow (pCf). Comparing the co-flow system with conventional pCf system, the former exhibits greater vorticity, vortex stretching, and kinetic energy. A detailed analysis on the geometry and topology of flow structures was studied using flow invariants.
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TL;DR: In this article, a review of recent developments in the physics and modeling of interfacial layers between regions with different turbulent intensities is presented, focusing on the case of turbulent/nonturbulent interfaces that exist at the edges of jets, wakes, mixing layers, and boundary layers.
Abstract: Recent developments in the physics and modeling of interfacial layers between regions with different turbulent intensities are reviewed. The flow dynamics across these layers governs exchanges of mass, momentum, energy, and scalars (e.g., temperature), which determine the growth, spreading, mixing, and reaction rates in many flows of engineering and natural interest. Results from several analytical and linearized models are reviewed. Particular attention is given to the case of turbulent/nonturbulent interfaces that exist at the edges of jets, wakes, mixing layers, and boundary layers. The geometry, dynamics, and scaling of these interfaces are reviewed, and future lines of research are suggested. The dynamics of passive and active scalars is also discussed, including the effects of stratification, turbulence level, and internal forcing. Finally, the modeling challenges for one-point closures and subgrid-scale models are briefly mentioned.
225 citations
TL;DR: In this paper, a zonal grid algorithm for direct numerical simulation (DNS) of incompressible turbulent flows within a Finite-Volume framework is presented, which uses fully coupled embedded grids and a conservative treatment of the grid-interface variables.
200 citations
TL;DR: In this paper, the Fourier spectrum along the direction of variation of the pattern is presented, and the component corresponding to the pattern wavenumber is investigated as an order parameter.
Abstract: Near transition, plane Couette flow takes the form of large-scale, oblique, and statistically steady alternating bands of turbulent and laminar flow. Properties of these flows are investigated using direct numerical simulation in a tilted computational domain. Four regimes—uniform, intermittent, periodic, and localized—are characterized. The Fourier spectrum along the direction of variation of the pattern is presented, and the component corresponding to the pattern wavenumber is investigated as an order parameter. The mean flow of a periodic pattern is characterized and shown to lead to a relation between the Reynolds number and the wavelength and angle of a pattern.
80 citations
TL;DR: The extensive numerical results for flow in a box of width 2pi and length 8pi presented here show that while the lifetimes increase rapidly with Reynolds number, they do not indicate a divergence and therefore no transition to persistent turbulence.
Abstract: Plane Couette flow, the flow between two parallel plates moving in opposite directions, belongs to the group of shear flows where turbulence occurs while the laminar profile is stable. Experimental and numerical studies show that at intermediate Reynolds numbers turbulence is transient and that the lifetimes are distributed exponentially. However, these studies have remained inconclusive about a divergence in lifetimes above a critical Reynolds number. The extensive numerical results for flow in a box of width 2\ensuremath{\pi} and length 8\ensuremath{\pi} presented here cover observation times up to $12\text{ }000$ units and show that while the lifetimes increase rapidly with Reynolds number, they do not indicate a divergence and therefore no transition to persistent turbulence.
39 citations
TL;DR: In this paper, a bilateral mixing-layer exists in the junction between co-flowing laminar and turbulent plane Couette flows, where the mixing zone varied with the distance from the stationary wall.
Abstract: A new flow configuration has been proposed in which a bilateral mixing-layer exists in the junction between co-flowing laminar and turbulent plane Couette flows. Contrary to a classical plane mixing-layer, the present mixing-layer did neither grow in time nor in streamwise direction. However, the mixing zone varied with the distance from the stationary wall. A direct numerical simulation showed that very-large-scale flow structures were found in the turbulent part of the flow with Reynolds number 1300 based on half the velocity U1 of the fastest-moving wall and half of the distance 2h between the walls. The laminar-turbulent interface exhibited a large-scale meandering motion with frequency 0.014U1/h and wavelength about 25h. Large-scale Taylor-Gortler-like roll cells were observed in the nominally laminar flow region with Reynolds number 260. This tailor-made flow is particularly well suited for explorations of momentum transfer and intermittency in the vicinity of the laminar-turbulent interface.
9 citations