Advection and Diffusion Simulations Using Lagrangian Blocks

Chu, Vincent H.; Altai, Wihel

doi:10.1615/ichmt.2012.cht-12.270

Cited by 2 publications

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“…The success of the present LES for the buoyancy effect on turbulence is directly attributable to the use of the Lagrangian block simulation method, which has been shown to produce simulation results without cumulative false diffusion error [7]. The Lagrangain block simulation also has been shown to have excellent numerical computational stability in a series of simulations for different problems [7] [12].…”

Section: Resultsmentioning

confidence: 85%

“…The Lagrangain block simulation also has been shown to have excellent numerical computational stability in a series of simulations for different problems [7] [12]. The solid lines are the results of the K-ε modelling simulations obtained from three buoyancy-extended modelling constants.…”

Section: Resultsmentioning

confidence: 97%

“…Occasional switching to a diffusive upwind scheme is one classic strategy to manage the numerical oscillations [1,2,3,4,5]. Lagrangian block simulation (LBS) offers an alternative that could eliminate the spurious numerical oscillations and false diffusive error [6,7]. The blocks move in the direction of the flow.…”

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confidence: 99%

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Lagrangian Block Simulation of Buoyancy at Turbulence Interfaces

Chu

Altai

2015

Comput Thermal Scien

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Simulations of turbulent interfaces produced by positive and negative buoyancy are conducted by moving blocks of fluid in the direction of the flow. The second moment of the blocks increases at a rate proportional to the diffusivity. The block simulation is free of numerical oscillations. Unlike most classical methods, the error associated with Lagrangian block simulation is not cumulative. Artificial diffusion error is negligible. The non-diffusive Lagrangian block simulations have provided reliable data to evaluate the performance of (i) sub-grid scale modelling and (ii) K-ε modelling of turbulent flow under the opposing influence of buoyancy. INTRODUCTIONMost computational fluid-dynamics codes are developed using the Eulerian description. To find the numerical solution, fluxes are estimated on the surface of the finite volume using a truncation series. Spurious numerical oscillations and artificial numerical diffusion are consequences, particularly in regions across flow discontinuities. Diffusion often is introduced synthetically in many schemes to gain computational stability. Occasional switching to a diffusive upwind scheme is one classic strategy to manage the numerical oscillations [1,2,3,4,5]. Lagrangian block simulation (LBS) offers an alternative that could eliminate the spurious numerical oscillations and false diffusive error [6,7]. The blocks move in the direction of the flow. The squares of the block widths expand in proportion to the diffusivities. The block simulation procedure consists of three steps: (i) Lagrangian advection and diffusion, (ii) division into portions, and (iii) reassembly of the portions into new blocks. The blocks are renewed in each time increment to prevent excessive distortion. In this paper simulation of buoyancy at turbulence interfaces has been carried out using the LBS method. In one series of simulations, the Kelvin-Helmholtz instabilities initiate turbulence across

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Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 97%

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Lagrangian Block Simulation of Buoyancy at Turbulence Interfaces

Chu

Altai

2015

Comput Thermal Scien

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“…Tan and Chu [26,27] validated their LBS of wet water on dry bed by the exact analytical solution. Chu and Altai [4][5][6] compared their LBS of the laminar-and-turbulent interfaces with the experimental observations. In this paper, the numerical accuracy is assessed by the energy consideration in Sect.…”

Section: Energy Conservation and Computational Errormentioning

confidence: 99%

“…Fluxes are not estimated so there are no numerical oscillation and diffusion errors from the truncation. Validation of the LBS method has been conducted in the calculation for the advance of wet water on dry bed by Tan and Chu [26,27] and in the simulations for the laminar-and-turbulent interfaces by Chu and Altai [4][5][6]. In the absence of spurious oscillations and false diffusion, the best possible inviscid model of the gravity-current head is constructed by the LBS.…”

Section: Introductionmentioning

confidence: 99%

A two-dimensional inviscid model of the gravity-current head by Lagrangian block simulation

Chu

Altai

2017

Environ Fluid Mech

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A two-dimensional inviscid model of the gravity-current head produced by the release of a relatively small volume of dense fluid from behind a tall lock gate is constructed by Lagrangian block simulation. Three numerical experiments are conducted for the lock's height-to-length aspect ratios H/L o = 8, 4 and 2. The front speeds obtained by the simulations agree with the laboratory observation for a similar range of aspect ratios. The floor velocity in the wake behind these heads is found to be greater than their front speed. The high floor velocity is caused by the impingement of the coherent wake vortex on the floor. It is a condition that permits these gravity-current heads to maintain their structural integrity so that the fine sediments can travel with the head over long distances on the ocean floor. The structural coherence of the current head depends on the lock aspect ratio. The gravity-current head produced by the release from the lock with the highest aspect ratio of H/L o = 8 is most coherent and relatively has the greatest floor velocity and the least trailing current behind the head.Keywords Gravity-current head Á Coherent wake vortex Á 2D inviscid model Á Lagrangian block advection Á Streamfunction and vorticity formulation

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Advection and Diffusion Simulations Using Lagrangian Blocks

Cited by 2 publications

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Lagrangian Block Simulation of Buoyancy at Turbulence Interfaces

Lagrangian Block Simulation of Buoyancy at Turbulence Interfaces

A two-dimensional inviscid model of the gravity-current head by Lagrangian block simulation

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