scholarly journals On the Equivalence of Two Schemes for Convective Momentum Transport

2012 ◽  
Vol 69 (12) ◽  
pp. 3491-3500 ◽  
Author(s):  
David M. Romps
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Mass Flux ◽  
Deep Convection ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Convective Momentum Transport

Abstract The Gregory–Kershaw–Inness (GKI) parameterization of convective momentum transport, which has a tunable parameter C, is shown to be identical to a parameterization with no pressure gradient force and a mass flux smaller by a factor of 1 − C. Using cloud-resolving simulations, the transilient matrix for momentum is diagnosed for deep convection in radiative–convective equilibrium. Using this transilient matrix, it is shown that the GKI scheme underestimates the compensating subsidence of momentum by a factor of 1 − C, as predicted. This result is confirmed using a large-eddy simulation.

Analysis of Submarine Pipeline Scour Using Large-Eddy Simulation of Dense Particle-Liquid Flows

2008 ◽  
Author(s):  
Piroz Zamankhan ◽  
Amir Ali Doolatshahi
Keyword(s):  
Large Eddy Simulation ◽  
Seepage Flow ◽  
Contact Forces ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Submarine Pipeline ◽  
Dense Particle ◽  
Eddy Simulation ◽  
Unidirectional Flow ◽  
Large Eddy

Using large-eddy simulation technique for dense particle-fluid flows, the current-induced scour is predicted for both the mono- and bi-dispersed systems below a horizontal submarine pipeline exposed to unidirectional flow. The simulations are four-way coupled, which implies that both solid-liquid and solid-solid interactions are taken into account. Particles are assumed to behave as visco-elastic solids during interactions with their neighboring particles, and their motion are predicted by a Lagrangian method. The inter-particle normal and tangential contact forces between particles are calculated using a generalized Hertzian model. The other forces on a particle that are taken into account include gravitational, pressure gradient force accounting for the acceleration of the displaced liquid, the drag force resulting from velocity difference with the surrounding liquid, and the Magnus and Saffman lift forces. The predicted scour profiles for monodispersed system are found to compare favorably with the laboratory observations. For the bi-dispersed system, a seepage flow underneath the pipe (which is a major factor to cause the onset of scour below the pipeline) is found to be weakened using an appropriate size for the sand bed. This finding highlights the importance of the bed particle size distribution on the onset of scour below the pipelines.

Analysis of Submarine Pipeline Scour Using Large-Eddy Simulation of Dense Particle-Liquid Flows

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Piroz Zamankhan
Keyword(s):  
Large Eddy Simulation ◽  
Seepage Flow ◽  
Contact Forces ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Submarine Pipeline ◽  
Dense Particle ◽  
Eddy Simulation ◽  
Unidirectional Flow ◽  
Large Eddy

Using large-eddy simulation technique for dense particle-fluid flows, the current-induced scour is predicted for both the mono- and bidispersed systems below a horizontal submarine pipeline exposed to unidirectional flow. The simulations are four-way coupled, which implies that both solid-liquid and solid-solid interactions are taken into account. Particles are assumed to behave as viscoelastic solids during interactions with their neighboring particles, and their motion are predicted by a Lagrangian method. The interparticle normal and tangential contact forces between particles are calculated using a generalized Hertzian model. The other forces on a particle that are taken into account include gravitational pressure gradient force accounting for the acceleration of the displaced liquid, the drag force resulting from velocity difference with the surrounding liquid, and the Magnus and Saffman lift forces. The predicted scour profiles for monodispersed system are found to compare favorably with the laboratory observations. For the bidispersed system, a seepage flow underneath the pipe (which is a major factor to cause the onset of scour below the pipeline) is found to be weakened using an appropriate size for the sand bed. This fiffnding highlights the importance of the bed particle size distribution on the onset of scour below the pipelines.

scholarly journals Sensitivity of Hurricane Intensity Forecast to Convective Momentum Transport Parameterization

2006 ◽  
Vol 134 (2) ◽  
pp. 664-674 ◽  
Author(s):  
Jongil Han ◽  
Hua-Lu Pan
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Momentum Exchange ◽  
Forecast System ◽  
Hurricane Intensity ◽  
Convective Momentum Transport ◽  
The Many

Abstract A parameterization of the convection-induced pressure gradient force (PGF) in convective momentum transport (CMT) is tested for hurricane intensity forecasting using NCEP's operational Global Forecast System (GFS) and its nested Regional Spectral Model (RSM). In the parameterization the PGF is assumed to be proportional to the product of the cloud mass flux and vertical wind shear. Compared to control forecasts using the present operational GFS and RSM where the PGF effect in CMT is taken into account empirically, the new PGF parameterization helps increase hurricane intensity by reducing the vertical momentum exchange, giving rise to a closer comparison to the observations. In addition, the new PGF parameterization forecasts not only show more realistically organized precipitation patterns with enhanced hurricane intensity but also reduce the forecast track error. Nevertheless, the model forecasts with the new PGF parameterization still largely underpredict the observed intensity. One of the many possible reasons for the large underprediction may be the absence of hurricane initialization in the models.

scholarly journals Large-eddy simulation of the zero-pressure-gradient turbulent boundary layer up to Reθ = O(1012)

2011 ◽  
Vol 686 ◽  
pp. 507-533 ◽  
Author(s):  
M. Inoue ◽  
D. I. Pullin
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Turbulent Boundary Layer ◽  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Skin Friction Coefficient ◽  
Smooth Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Near Wall

AbstractA near-wall subgrid-scale (SGS) model is used to perform large-eddy simulation (LES) of the developing, smooth-wall, zero-pressure-gradient flat-plate turbulent boundary layer. In this model, the stretched-vortex, SGS closure is utilized in conjunction with a tailored, near-wall model designed to incorporate anisotropic vorticity scales in the presence of the wall. Large-eddy simulations of the turbulent boundary layer are reported at Reynolds numbers ${\mathit{Re}}_{\theta } $ based on the free-stream velocity and the momentum thickness in the range ${\mathit{Re}}_{\theta } = 1{0}^{3} \text{{\ndash}} 1{0}^{12} $. Results include the inverse square-root skin-friction coefficient, $ \sqrt{2/ {C}_{f} } $, velocity profiles, the shape factor $H$, the von Kármán ‘constant’ and the Coles wake factor as functions of ${\mathit{Re}}_{\theta } $. Comparisons with some direct numerical simulation (DNS) and experiment are made including turbulent intensity data from atmospheric-layer measurements at ${\mathit{Re}}_{\theta } = O(1{0}^{6} )$. At extremely large ${\mathit{Re}}_{\theta } $, the empirical Coles–Fernholz relation for skin-friction coefficient provides a reasonable representation of the LES predictions. While the present LES methodology cannot probe the structure of the near-wall region, the present results show turbulence intensities that scale on the wall-friction velocity and on the Clauser length scale over almost all of the outer boundary layer. It is argued that LES is suggestive of the asymptotic, infinite Reynolds number limit for the smooth-wall turbulent boundary layer and different ways in which this limit can be approached are discussed. The maximum ${\mathit{Re}}_{\theta } $ of the present simulations appears to be limited by machine precision and it is speculated, but not demonstrated, that even larger ${\mathit{Re}}_{\theta } $ could be achieved with quad- or higher-precision arithmetic.

scholarly journals ANÁLISE DA PROPAGAÇÃO E MANUTENÇÃO DOS VÓRTICES GERADOS POR UM MICROBURST ESTÁTICO E ISOLADO

2016 ◽  
Vol 38 ◽  
pp. 41
Author(s):  
Giuliano Demarco ◽  
Vagner Anabor ◽  
Umberto Rizza ◽  
Franciano Scremin Puhales ◽  
Luís Gustavo Nogueira Martins ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Large Eddy Simulation ◽  
Vortex Ring ◽  
Deep Convection ◽  
Extreme Weather Events ◽  
Dynamical Process ◽  
Eddy Simulation ◽  
Wind Gusts ◽  
Weather Events ◽  
Large Eddy

The Southern Brazilian region is specially affected by extreme weather events, very often intense wind gusts coming from deep convection may develop itself as a microburst producing winds higher than 100 km/h. In order to understand the physical and dynamical process evolved in this phenomena, a static and isolated microburst is produced through a Large Eddy Simulation. A quantitative analysis of propagation an maintenance of the microburst vortex ring is performed in order to understand its evolution.

scholarly journals A New Wall Model for Large Eddy Simulation of Separated Flows

Fluids ◽  
2019 ◽  
Vol 4 (4) ◽  
pp. 197 ◽  
Author(s):  
Ahmad Fakhari
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Separated Flows ◽  
Two Dimensional ◽  
Wall Model ◽  
Law Of The Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Immersed Boundaries ◽  
Near Wall

The aim of this work is to propose a new wall model for separated flows which is combined with large eddy simulation (LES) of the flow field in the whole domain. The model is designed to give reasonably good results for engineering applications where the grid resolution is generally coarse. Since in practical applications a geometry can share body fitted and immersed boundaries, two different methodologies are introduced, one for body fitted grids, and one designed for immersed boundaries. The starting point of the models is the well known equilibrium stress model. The model for body fitted grid uses the dynamic evaluation of the von Kármán constant κ of Cabot and Moin (Flow, Turbulence and Combustion, 2000, 63, pp. 269–291) in a new fashion to modify the computation of shear velocity which is needed for evaluation of the wall shear stress and the near-wall velocity gradients based on the law of the wall to obtain strain rate tensors. The wall layer model for immersed boundaries is an extension of the work of Roman et al. (Physics of Fluids, 2009, 21, p. 101701) and uses a criteria based on the sign of the pressure gradient, instead of one based on the friction velocity at the projection point, to construct the velocity under an adverse pressure gradient and where the near-wall computational node is in the log region, in order to capture flow separation. The performance of the models is tested over two well-studied geometries, the isolated two-dimensional hill and the periodic two-dimensional hill, respectively. Sensitivity analysis of the models is also performed. Overall, the models are able to predict the first and second order statistics in a reasonable way, including the position and extension of the downward separation region.

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