scholarly journals Where is the Interface of the Stratocumulus-Topped PBL?

2005 ◽  
Vol 62 (7) ◽  
pp. 2626-2631 ◽  
Author(s):  
C-H. Moeng ◽  
B. Stevens ◽  
P. P. Sullivan
Keyword(s):  
Turbulent Mixing ◽  
Grid Spacing ◽  
Free Atmosphere ◽  
Maximum Gradient ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Vertical Grid ◽  
Fine Resolution ◽  
Local Cloud ◽  
Simulated Flow

Abstract Various locally defined (not horizontal mean) interfaces between the stratocumulus-topped PBL and the free atmosphere are investigated using a fine-resolution large-eddy simulation with a vertical grid spacing of about 4 m. The local cloud-top height is found to be always below the height where the maximum gradient of the local sounding occurs, and the maximum-gradient height is always below the interface where PBL air can reach via turbulent motions. The distances between these local interfaces are of significant amount, a few tens of meters on average. Air between the cloud-top and maximum-gradient interfaces is fully turbulent, unsaturated, but rather moist. Air between the maximum-gradient and turbulent-mixing interfaces consists of turbulent motions that are intermittent in space and time. The simulated flow shows no clearly defined interface that separates cloudy, turbulent air mass from clear, nonturbulent air above, even locally.

scholarly journals Fine-Scale Structures in the Mid-Level Eyewall of Super Typhoon Rammasun (2014) Simulated With the WRF-LES Framework

2022 ◽  
Vol 9 ◽  
Author(s):  
Zhen Gao ◽  
Liguang Wu ◽  
Xingyang Zhou
Keyword(s):  
Tropical Cyclone ◽  
Three Dimensional ◽  
Wrf Model ◽  
Rapid Intensification ◽  
Grid Spacing ◽  
Super Typhoon ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Vertical Grid ◽  
Horizontal Grid

It has been numerically demonstrated that the turbulence above the boundary is important to tropical cyclone intensification and rapid intensification, but the three-dimensional structures of the sub-grid-scale (SGS) eddy have not been revealed due to the lack of observational data. In this study, two numerical simulations of Super Typhoon Rammasun (2014) were conducted with the Advanced Weather Research and Forecast (WRF) model by incorporating the large-eddy simulation (LES) technique, in which the enhanced eyewall convection and the process of rapid intensification are captured. Consistent with previous observational studies, the strong turbulent kinetic energy (TKE) is found throughout the whole eyewall inside of the radius of maximum wind in both experiments. The simulations indicate that the strong TKE is associated with horizontal rolls with the horizontal extent of 2–4 km, which are aligned azimuthally in the intense eyewall convection. It is indicated that the three-dimensional structures of the SGS eddy can be simulated with the vertical grid spacing of ∼100 m when the horizontal grid spacing is 74 m. It is suggested that there is considerable turbulence associated with azimuthally-aligned horizontal rolls in the mid-level eyewall of tropical cyclone.

scholarly journals Implicit large eddy simulation of shock-driven material mixing

2013 ◽  
Vol 371 (2003) ◽  
pp. 20120217 ◽  
Author(s):  
F. F. Grinstein ◽  
A. A. Gowardhan ◽  
J. R. Ristorcelli
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Mixing ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Late Time ◽  
Eddy Simulation ◽  
Geometrical Complexity ◽  
Planar Shock ◽  
Large Eddy ◽  
Implicit Large Eddy Simulation

Under-resolved computer simulations are typically unavoidable in practical turbulent flow applications exhibiting extreme geometrical complexity and a broad range of length and time scales. An important unsettled issue is whether filtered-out and subgrid spatial scales can significantly alter the evolution of resolved larger scales of motion and practical flow integral measures. Predictability issues in implicit large eddy simulation of under-resolved mixing of material scalars driven by under-resolved velocity fields and initial conditions are discussed in the context of shock-driven turbulent mixing. The particular focus is on effects of resolved spectral content and interfacial morphology of initial conditions on transitional and late-time turbulent mixing in the fundamental planar shock-tube configuration.

scholarly journals Large-Eddy Simulation of Roll Vortices in a Hurricane Boundary Layer

2012 ◽  
Vol 69 (12) ◽  
pp. 3558-3575 ◽  
Author(s):  
Mikio Nakanishi ◽  
Hiroshi Niino
Keyword(s):  
Large Eddy Simulation ◽  
Ground Surface ◽  
Internal Gravity Waves ◽  
Eof Analysis ◽  
Free Atmosphere ◽  
Eddy Simulation ◽  
Roll Vortices ◽  
Large Eddy ◽  
Radial Velocity Profile ◽  
Hurricane Boundary Layer

Abstract For the last decade, horizontal roll vortices have been often observed in hurricane boundary layers (HBLs). In this study, a large-eddy simulation is performed to explore the formation mechanism of the horizontal roll vortices and their significance in a near-neutrally stratified HBL at 40 km (R40) and 100 km (R100) from the center of the hurricane. Results are examined through turbulence statistics and empirical orthogonal function (EOF) analysis. The EOF analysis and budgets of turbulent kinetic energy demonstrate that an inflection-point instability in the radial velocity profile is responsible for the roll vortices with horizontal wavelengths of 1.5–2.4 km in the HBL both for R40 and R100. The roll vortices for R40 are nearly aligned with the gradient wind, while those for R100 are oriented slightly to the left of that wind. Also the horizontal distributions of velocity fluctuations suggest the presence of streaklike structures at horizontal intervals of several hundred meters near the ground surface. Internal gravity waves, Kelvin–Helmholtz waves, and entrainments occur above the HBL and are partly coupled with the roll vortices in the HBL, implying an enhancement of vertical transports of momentum and other quantities between the HBL and the free atmosphere.

scholarly journals Stably Stratified Flows: A Model with No Ri(cr)*

2008 ◽  
Vol 65 (7) ◽  
pp. 2437-2447 ◽  
Author(s):  
V. M. Canuto ◽  
Y. Cheng ◽  
A. M. Howard ◽  
I. N. Esau
Keyword(s):  
Numerical Simulation ◽  
Large Eddy Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Mixing ◽  
Stratified Flows ◽  
The Other ◽  
Large Set ◽  
Eddy Simulation ◽  
Stably Stratified Flows ◽  
Large Eddy

Abstract A large set of laboratory, direct numerical simulation (DNS), and large eddy simulation (LES) data indicates that in stably stratified flows turbulent mixing exists up to Ri ∼ O(100), meaning that there is practically no Ri(cr). On the other hand, traditional local second-order closure (SOC) models entail a critical Ri(cr) ∼ O(1) above which turbulence ceases to exist and are therefore unable to explain the above data. The authors suggest how to modify the recent SOC model of Cheng et al. to reproduce the above data for arbitrary Ri.

Analysis and Optimization of Turbulent Mixing With Large Eddy Simulation

2006 ◽  
Author(s):  
Ying Huai ◽  
Amsini Sadiki
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Mixing ◽  
Optimization Procedure ◽  
Impinging Jet ◽  
Computational Domain ◽  
Original Design ◽  
Mixing Processes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Practical Engineering

In this work, Large Eddy Simulation (LES) has been carried out to analyze the turbulent mixing processes in an impinging jet configuration. To characterize and quantify turbulent mixing processes, in terms of scalar structures and degree of mixing, three parameters have been basically introduced. They are “mixedness parameter”, which represents the probability of mixed fluids in computational domain, the Spatial Mixing Deficiency (SMD) and the Temporal Mixing Deficiency (TMD) parameters for characterizing the mixing at different scalar scale degrees. With help of these parameters, a general mixing optimization procedure has then been suggested and achieved in an impinging jet configuration. An optimal jet angle was estimated and the overall mixing degree with this jet angle reached around six times more than the original design. It turns out that the proposed idea and methodology can be helpful for practical engineering design processes.

scholarly journals Dealing with uncertainty: turbulent parameterizations and grid-spacing effects in numerical modelling of deep moist convective processes

2009 ◽  
Vol 9 (6) ◽  
pp. 1871-1880 ◽  
Author(s):  
E. Fiori ◽  
A. Parodi ◽  
F. Siccardi
Keyword(s):  
Weather Prediction ◽  
Predictive Ability ◽  
Grid Spacing ◽  
Eddy Simulation ◽  
Fine Mesh ◽  
Spacing Effects ◽  
Weather Events ◽  
Large Eddy ◽  
Turbulent Closure ◽  
Ground Effects

Abstract. Computer power has grown to the point that very-fine-mesh mesoscale modelling is now possible. Going down through scales is clumsily supposed to reduce uncertainty and to improve the predictive ability of the models. This work provides a contribution to understand how the uncertainty in the numerical weather prediction (NWP) of severe weather events is affected by increasing the model grid resolution and by choosing a parameterization which is able to represent turbulent processes at such finer scales. A deep moist convective scenario, a supercell, in a simplified atmospheric setting is studied by mean of high resolution numerical simulations with COSMO-Model. Different turbulent closures are used and their impacts on the space-time properties of convective fields are discussed. The convective-resolving solutions adopting Large Eddy Simulation (LES) turbulent closure converge with respect to the overall flow field structure when grid spacing is properly reduced. By comparing the rainfall fields produced by the model on larger scales with those at the convergence scales it's possible to size up the uncertainty introduced by the modelling itself on the predicted ground effects in such simplified scenario.

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