Large-eddy simulation of starting buoyant jets

Wang, Ruo‐Qian; Law, Adrian Wing‐Keung; Adams, E. Eric; Fringer, Oliver B.

doi:10.1007/s10652-010-9201-0

Cited by 24 publications

(9 citation statements)

References 34 publications

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“…The current observation of peaks and humps in the axial concentration profile are consistent with trends from direct numerical (Picano et al 2010) and large eddy (Wang et al 2013) simulations of turbulent particle-laden free jets. The DNS data of Picano et al taken at Sk D = 1.0 and 2.0 are similar to the current measurements at Sk D = 1.4 and 2.8 (see figure 16), with the magnitude and axial location of the peak Θ c /Θ ec approximately equal.…”

Section: Concentration Measurementssupporting

confidence: 85%

The effect of Stokes number on particle velocity and concentration distributions in a well-characterised, turbulent, co-flowing two-phase jet

Lau

Nathan

2016

J. Fluid Mech.

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Simultaneous measurements of particle velocity and concentration (number density) in a series of mono-disperse, two-phase turbulent jets issuing from a long, round pipe into a low velocity co-flow were performed using planar nephelometry and digital particle image velocimetry. The exit Stokes number,$Sk_{D}$, was systematically varied over two orders of magnitude between 0.3 and 22.4, while the Reynolds number was maintained in the turbulent regime ($10\,000\leqslant Re_{D}\leqslant 40\,000$). The mass loading was fixed at$\unicode[STIX]{x1D719}=0.4$, resulting in a flow that is in the two-way coupling regime. The results show that, in contrast to all previous work where a single Stokes number has been used to characterise fluid–particle interactions, the characteristic Stokes number in the axial direction is lower than that for the radial direction. This is attributed to the significantly greater length scales in the axial motions than in the radial ones. It further leads to a preferential response of particles to gas-phase axial velocity fluctuations,$u_{p}^{\prime }$, over radial velocity fluctuations,$v_{p}^{\prime }$. This, in turn, leads to high levels of anisotropy in the particle-phase velocity fluctuations,$u_{p}^{\prime }/v_{p}^{\prime }>1$, throughout the jet, with$u_{p}^{\prime }/v_{p}^{\prime }$increasing as$Sk_{D}$is increased. The results also show that the region within the first few diameters of the exit plane is characterised by a process of particle reorganisation, resulting in significant particle migration to the jet axis for$Sk_{D}\leqslant 2.8$and away from the axis for$Sk_{D}\geqslant 5.6$. This migration, together with particle deceleration along the axis, causes local humps in the centreline concentration whose value can even exceed those at the exit plane.

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Section: Concentration Measurementssupporting

confidence: 85%

The effect of Stokes number on particle velocity and concentration distributions in a well-characterised, turbulent, co-flowing two-phase jet

Lau

Nathan

2016

J. Fluid Mech.

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“…Momentum advection is accomplished with the QUICK scheme of Leonard [] and scalar advection is accomplished with the SHARP scheme [ Leonard , ]. This code has been used for many environmental flow applications, including upwelling flow [ Cui and Street , ], buoyant jets [ Wang et al ., ], sediment transport [ Zedler and Street , ; Chou and Fringer , ], internal gravity waves [ Fringer and Street , ; Arthur and Fringer , ], and internal bolus formation [ Venayagamoorthy and Fringer , ]. Thus, we can assert that this code has been successfully used to study the gravity current hydrodynamics within stratified systems.…”

Section: Methodsmentioning

confidence: 99%

Numerical investigation of split flows by gravity currents into two-layered stratified water bodies

Cortés

Wells

Fringer

et al. 2015

J. Geophys. Res. Oceans

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The behavior of a two‐dimensional (2‐D) gravity current impinging upon a density step in a two‐layered stratified basin is analyzed using a high‐resolution Reynolds‐Averaged Navier‐Stokes model. The gravity current splits at the density step, and the portion of the buoyancy flux becoming an interflow is largely controlled by the vertical distribution of velocity and density within the gravity current and the magnitude of the density step between the two ambient layers. This is in agreement with recent laboratory observations. The strongest changes in the ambient density profiles occur as a result of the impingement of supercritical currents with strong density contrasts, for which a large portion of the gravity current detaches from the bottom and becomes an interflow. We characterize the current partition process in the simulated experiments using the densimetric Froude number of the current (Fr) across the density step (upstream and downstream). When underflows are formed, more supercritical currents are observed downstream of the density step compared to upstream (Fru < Frd), and thus, stronger mixing of the current with the ambient water downstream. However, when split flows and interflows are formed, smaller Fr values are identified after the current crosses the density step (Fru > Frd), which indicates lower mixing between the current and ambient water after the impingement due to the significant stripping of interfacial material at the density step.

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“…Turbulent plume pinch-off and the transition from a pure to a stopping plume (analogous to a 'starting plume' [36,39]) are experimentally examined. A schematic representation of the experimental apparatus is shown in Fig.…”

Section: Experimental Arrangementmentioning

confidence: 99%

Turbulent ‘stopping plumes’ and plume pinch-off in uniform surroundings

Kattimeri

Scase

2014

Environ Fluid Mech

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Observations of turbulent convection in the environment are of variously sustained plume-like flows or intermittent thermal-like flows. At different times of the day the prevailing conditions may change and consequently the observed flow regimes may change. Understanding the link between these flows is of practical importance meteorologically, and here we focus our interest upon plume-like regimes that break up to form thermal-like regimes. It has been shown that when a plume rises from a boundary with low conductivity, such as arable land, the inability to maintain a rapid enough supply of buoyancy to the plume source can result in the turbulent base of the plume separating and rising away from the source. This plume 'pinch-off' marks the onset of the intermittent thermal-like behavior.The dynamics of turbulent plumes in a uniform environment are explored in order to investigate the phenomenon of plume pinch-off. The special case of a turbulent plume having its source completely removed, a 'stopping plume', is considered in particular. The effects of forcing a plume to pinch-off, by rapidly reducing the source buoyancy flux to zero, are shown experimentally. We release saline solution into a tank filled with fresh water generating downward propagating steady turbulent plumes. By rapidly closing the plume nozzle, the plumes are forced to pinch-off. The plumes are then observed to detach from the source and descend into the ambient. The unsteady buoyant region produced after pinch-off, cannot be described by the power-law behavior of either classical plumes or thermals, and so the terminology 'stopping plume' (analogous to a 'starting plume') is adopted for this type of flow. The propagation of the stopping plume is shown to be approximately linearly dependent on time, and we speculate therefore that the closure of the nozzle introduces some vorticity into the ambient, that may roll up to form a vortex ring dominating the dynamics of the base of a stopping plume.

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Large-eddy simulation of starting buoyant jets

Cited by 24 publications

References 34 publications

The effect of Stokes number on particle velocity and concentration distributions in a well-characterised, turbulent, co-flowing two-phase jet

The effect of Stokes number on particle velocity and concentration distributions in a well-characterised, turbulent, co-flowing two-phase jet

Numerical investigation of split flows by gravity currents into two-layered stratified water bodies

Turbulent ‘stopping plumes’ and plume pinch-off in uniform surroundings

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