Numerical study of hydrodynamic coefficients of multiple heave plates by large eddy simulations with volume of fluid method

A numerical study of turbulent channel flow at various Reynolds numbers (Reτ=115, 210, 300) is conducted in order to examine the requirements for a reliable subgrid modelling in large-eddy simulations of wall-bounded flows. Using direct numerical simulation data, the interactions between large and small scales in the near-wall flow are analysed in detail which sheds light on the origin of the inverse cascade of turbulent kinetic energy observed in the buffer layer. It is shown that the correlation of the wall-normal subgrid stress and the wall-normal derivative of the streamwise grid-scale velocity plays the key role in the occurrence of the inverse cascade. A brief a priori test of several subgrid models shows that currently applied models are not capable of accounting properly for the complex interactions in the near-wall flow. A series of large-eddy simulations gives evidence that this deficiency may cause significant errors in important global quantities of the flow such as the mean wall shear stress. A study of the eddy-viscosity ansatz is conducted which reveals that the characteristic scales usually employed for the definition of the eddy viscosity are inappropriate in the vicinity of a wall. Therefore, a novel definition of the eddy viscosity is derived from the analysis of the near-wall energy budget. This new definition, which employs the wall-normal subgrid stress as a characteristic scale, is more consistent with the near-wall physics. No significant Reynolds-number effects are encountered in the present analysis which suggests that the findings may be generalized to flows at higher Reynolds numbers.

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Is the water vapor supersaturation distribution Gaussian?

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0388.1 ◽

2021 ◽

Author(s):

Subin Thomas ◽

Prasanth Prabhakaran ◽

Will Cantrell ◽

Raymond A. Shaw

Keyword(s):

Water Vapor ◽

Large Eddy Simulation ◽

Gaussian Distribution ◽

Numerical Study ◽

Mixing Model ◽

Large Eddy Simulations ◽

Mixing Processes ◽

Eddy Simulation ◽

Large Eddy ◽

Vapor Supersaturation

AbstractWater vapor supersaturation in the atmosphere is produced in a variety of ways, including the lifting of a parcel or via isobaric mixing of parcels. However, irrespective of the mechanism of production, the water vapor supersaturation in the atmosphere has typically been modeled as a Gaussian distribution. In the current theoretical and numerical study, the nature of supersaturation produced by mixing processes is explored. The results from large eddy simulation and a Gaussian mixing model reveal the distribution of supersaturations produced by mixing to be negatively skewed. Further, the causes of skewness are explored using large eddy simulations (LES) and the Gaussian mixing model (GMM). The correlation in forcing of temperature and water vapor fields is recognized as playing a key role.

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Numerical Study of the Turbulent Flow Inside an ORACLES Configuration

Journal of Applied Mechanics ◽

10.1115/1.4006455 ◽

2012 ◽

Vol 79 (5) ◽

Cited By ~ 4

Author(s):

Fethi Bouras ◽

Azeddine Soudani ◽

Mohamed Si-Ameur

Keyword(s):

Eddy Viscosity ◽

Numerical Study ◽

Longitudinal Velocity ◽

Large Eddy Simulations ◽

The European Union ◽

Combustion Chambers ◽

Eddy Simulation ◽

Large Eddy ◽

Recirculation Zones ◽

Air Channels

This numerical investigation deals with the validation of the experimental results in the inert cases of Nguyen et al., obtained in the framework of the European Union-funded research program MOLECULES (Modelling of Low Emissions Combustors Using Large Eddy Simulations). This study is based on the benchmark of testing one rig for accurate comparisons with large eddy simulations configuration (ORACLES), aimed at helping the design of reliable lean premixed prevaporized) combustion chambers and supplied with two identical flows of air channels. Therefore, this study is based on the 3D numerical simulation using large eddy simulation-wall adapting local eddy viscosity (LES-WALE) model that aims to determine the longitudinal velocity, the longitudinal velocity fluctuation and the length of recirculation zone for the three cases of flow in different inlet Reynolds (Re = 25,000, 50,000, 75,000). Calculations are carried out by the FLUENT_CFD. The results obtained are compared with experimental measurements of Nguyen et al. The LES_WALE eddy viscosity computation presents a good agreement with the experimental data where we could observe the asymmetrical flow and also detect the recirculation zones and the differences between the cases of the flow.

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Numerical Study on the Rising Motion of Bubbles near the Wall

Applied Sciences ◽

10.3390/app112210918 ◽

2021 ◽

Vol 11 (22) ◽

pp. 10918

Author(s):

Kaixin Zhang ◽

Yongzheng Li ◽

Qi Chen ◽

Peifeng Lin

Keyword(s):

Numerical Study ◽

Bubble Diameter ◽

Interaction Force ◽

Volume Of Fluid ◽

Volume Of Fluid Method ◽

Wall Surface ◽

Bubble Wall ◽

Wall Distance ◽

Static Water ◽

Double Bubbles

Based on the volume of fluid method (VOF), the rising characteristics of bubbles in near-wall static water are studied. In this study, the influence of the wall on the rising motion of the bubble was studied by changing the distance of the bubble wall, the diameter of the bubble, the arrangement of the bubble and the size ratio, etc. The influence is expressed as the average swing amplitude of the “Z”-shaped motion when the bubble rises. The study found that in the case of a single bubble, the wall surface has a certain influence on the rise of the bubble, and its degree is affected by the bubble wall distance and the bubble diameter. The influence of bubble wall distance is more obvious. The greater the bubble wall distance, the less the bubble is affected by the wall; in the case of double bubbles, the influence of the interaction force between the bubbles is significantly greater than the wall surface.

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