scholarly journals Solid Boundary as Energy Source and Sink in a Dry Granular Dense Flow: A Comparison between Two Turbulent Closure Models

Engineering ◽  
2014 ◽  
Vol 06 (13) ◽  
pp. 960-972
Author(s):  
Chung Fang
Keyword(s):  
Energy Source ◽  
Solid Boundary ◽  
Closure Models ◽  
Turbulent Closure ◽  
Dense Flow ◽  
Source And Sink

Invariance of turbulent closure models

1979 ◽  
Vol 22 (6) ◽  
pp. 1033 ◽  
Author(s):  
Charles G. Speziale
Keyword(s):  
Closure Models ◽  
Turbulent Closure

scholarly journals Pumping of Strong H2O Cosmic Masers

1980 ◽  
Vol 87 ◽  
pp. 591-592
Author(s):  
V. S. Strelnitsky
Keyword(s):  
Energy Source ◽  
Flux Density ◽  
Cross Section ◽  
Rotational Level ◽  
Line Of Sight ◽  
Number Density ◽  
Pump Rate ◽  
Cosmic Masers ◽  
Strong Source ◽  
Source And Sink

All the existing models of H2O masers fail to explain such a strong source as W49 N. Observed and theoretical quantities are related by: nH2OWPℓ3 ≳ 1046 S, where S is the maser flux density (in Janskys), nH2O is the H2O number density (cm−3), Wp is pump rate (s−1), and ℓ is the length of amplification region on the line of sight (cm). Models involving vibrational activation (or deactivation) of H2O by H2 (Goldreich and Kwan, 1974; Norman and Silk, 1979), with the usual cross-section σν ≲ 10−19cm2, require ℓ > 1016 cm for the strongest H2O features (∼104 Jy), which is unacceptable in view of the VLBI results. Besides, because σν is so small, it is questionable if vibrational pumping could control rotational level populations at all. Depending on the energy source and sink there are four possible schemes of rotational pumping: CR, RC, RR, and CC (C - collisional, R - radiative). The first was modelled by de Jong (1973) and by Shmeld et al. (1976). Though difficulties with the sink (Goldreich and Kwan, 1974; 1979) are avoidable in the model by Shmeld et al. (Strelnitsky, 1979), ℓ ≳ 1015 − 1016 cm is still required for the strongest features. Therefore other possibilities of rotational pumping are being investigated. One CC-model is presented below.

scholarly journals Prediction of high-lift flows using turbulent closure models

1997 ◽  
Author(s):  
Christopher Rumsey ◽  
Thomas Gatski ◽  
Susan Ying ◽  
Arild Bertelrud ◽  
Arild Bertelrud ◽  
...  
Keyword(s):  
High Lift ◽  
Closure Models ◽  
Turbulent Closure

Influence of Velocity Slip on Turbulent Features of a Drygranular Dense Flow

2015 ◽  
Vol 31 (4) ◽  
pp. 457-465
Author(s):  
C. Fang
Keyword(s):  
Velocity Slip ◽  
Zero Order ◽  
Dynamic Responses ◽  
Solid Boundary ◽  
Boundary Layer Flows ◽  
Turbulent Dissipation ◽  
Entropy Principle ◽  
Dense Flow ◽  
Gravity Driven ◽  
Gravity Driven Flow

AbstractA zero-order turbulence closure model of a dry granular dense flow is proposed, with the boundary considered an energy source and sink of the turbulent kinetic energy of the grains. Muller-Liu entropy principle is carried out to derive the equilibrium closure relations, with their dynamic responses postulated from the experimental calibrations. A gravity-driven flow with incompressible grains down an inclined moving plane is studied to investigate the influence of velocity slip near solid boundary on the turbulent features of the flow. While the calculated mean porosity and velocity correspond to the experimental outcomes, increasing velocity slip on the boundary tends to enhance the turbulent dissipation nearby. The distribution of the turbulent dissipation shows a similarity with that of conventional Newtonian fluids in turbulent boundary layer flows. Boundary as an energy sink is more apparent in the zero-order model.

scholarly journals Energy Sources Generation and Energy Cascades along the Kuroshio East of Taiwan Island and the East China Sea

2021 ◽  
Vol 9 (7) ◽  
pp. 692
Author(s):  
Ru Wang ◽  
Yijun Hou ◽  
Ze Liu
Keyword(s):  
Energy Source ◽  
State Energy ◽  
Sea Surface ◽  
Energy Sources ◽  
Spectral Energy ◽  
The East China Sea ◽  
Energy Cascades ◽  
Taiwan Island ◽  
The Kuroshio ◽  
Source And Sink

There are multi-spatial-scale ocean dynamic processes in the western boundary current region, so the budget of energy source and sink in the Kuroshio Current area can describe the oceanic energy cycle and transformation more accurately. The slope of the one-dimensional spectral energy density varies between −5/3 and −3 in the wavenumber range of 0.02–0.1 cpkm, indicating an inverse energy cascade in the Kuroshio of Taiwan Island and the East China Sea. According to the steady-state energy evolution, an energy source must be present. The locations of energy sources were identified using the spectral energy transfer calculated by 24 years of Ocean General Circulation Model for the Earth Simulator (OFES) data. At the sea surface, the kinetic energy (KE) sources are mainly within 23.2°–25.6° Nand 28°–29° N at less than 0.02 cpkm and within 23.2°–25° N and 26°–30° N at 0.02–0.1 cpkm. The available potential energy (APE) sources are mainly within 22°–28° N and 28.6°–30° N at less than 0.02 cpkm and within22.6°–24.6° N, 25.4°–28° N and 29.2°–30° N at 0.02–0.1 cpkm. Beneath the sea surface, the energy sources are mainly above 400 m depth. Wind stress and density differences are primarily responsible for the KE and APE sources, respectively. Once an energy source is formed, to maintain a steady state, energy cascades (mainly inverse cascades by calculating spectral energy flux) will be engendered. By calculating the energy flux at 600 m depth, KE changes from inflow (sink) to outflow (source), and the conversion depth of source and sink is 380 m. However, outflow of the APE behaves as the source.

scholarly journals TURBULENCE MODELING IN GEOPHYSICAL FLOWS – PART I – FIRST-ORDER TURBULENT CLOSURE MODELING

2014 ◽  
Vol 32 (1) ◽  
pp. 31
Author(s):  
José Francisco Almeida de Souza ◽  
José Luiz Lima de Azevedo ◽  
Leopoldo Rota de Oliveira ◽  
Ivan Dias Soares ◽  
Maurício Magalhães Mata
Keyword(s):  
Turbulence Modeling ◽  
Turbulence Models ◽  
Transport Equations ◽  
Navier Stokes ◽  
Turbulent Length Scale ◽  
Second Moment ◽  
First Order ◽  
Closure Models ◽  
Turbulent Closure ◽  
Reynolds Averaged Navier Stokes

ABSTRACT. The usage of so-called turbulence closure models within hydrodynamic circulation models comes from the need to adequately describe vertical mixing processes. Even among the classical turbulence models; that is, those based on the Reynolds decomposition technique (Reynolds Averaged Navier-Stokes – RANS), there is a variety of approaches that can be followed for the modeling of turbulent flows (second moment) of momentum, heat, salinity, and other properties. Essentially, these approaches are divided into those which use the concept of turbulent viscosity/diffusivity in the modeling of the second moment, and those which do not use it. In this work we present and discuss the models that employ this concept, in which the viscosity can be considered constant or variable. In this latter scenario, besides those that use the concepts of mixture length, the models that use one or two differential transport equations for determining the viscosity are presented. The fact that two transport equations are used – one for the turbulent kinetic energy and the other for the turbulent length scale – make these latter ones the most complete turbulent closure models in this category. Keywords: turbulence modeling, turbulence models, first-order models, first-order turbulent closure.    RESUMO. A descrição adequada dos processos de mistura vertical nos modelos de circulação hidrodinâmica é o objetivo dos chamados modelos de turbulência, os quais são acoplados aos primeiros. Mesmo entre os modelos clássicos de turbulência, isto é, aqueles que se baseiam na técnica de decomposição de Reynolds (Reynolds Averaged Navier-Stokes – RANS), existe uma variedade de abordagens que podem ser seguidas na modelagem dos fluxos turbulentos (segundos momentos) de momentum, calor, salinidade e outras propriedades. Fundamentalmente estas abordagens dividem-se entre aquelas que utilizam o conceito de viscosidade/ difusividade turbulenta na modelagem dos segundos momentos, e aquelas que não o utilizam. Nesse trabalho são apresentados e discutidos os modelos que empregam este conceito, onde a viscosidade pode ser considerada constante ou variável. No caso variável, além daqueles que utilizam o conceito de comprimento de mistura, são ainda apresentados os modelos que utilizam uma ou duas equações diferenciais de transporte para a determinação da viscosidade. O fato de empregar duas equações de transporte, uma para a energia cinética turbulenta e outra para a escala de comprimento turbulento, fazem destes últimos os mais completos modelos de fechamento turbulento desta categoria. Palavras-chave: modelagem da turbulência, modelos de turbulência, modelos de primeira ordem, fechamento turbulento de primeira orde

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