scholarly journals Demistify: a large-eddy simulation (LES) and single-column model (SCM) intercomparison of radiation fog

2022 ◽  
Vol 22 (1) ◽  
pp. 319-333
Author(s):  
Ian Boutle ◽  
Wayne Angevine ◽  
Jian-Wen Bao ◽  
Thierry Bergot ◽  
Ritthik Bhattacharya ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Weather Prediction ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Radiation Fog ◽  
Eddy Simulation ◽  
Cloud Droplet Size Distribution ◽  
Large Eddy ◽  
Single Column ◽  
Les Model

Abstract. An intercomparison between 10 single-column (SCM) and 5 large-eddy simulation (LES) models is presented for a radiation fog case study inspired by the Local and Non-local Fog Experiment (LANFEX) field campaign. Seven of the SCMs represent single-column equivalents of operational numerical weather prediction (NWP) models, whilst three are research-grade SCMs designed for fog simulation, and the LESs are designed to reproduce in the best manner currently possible the underlying physical processes governing fog formation. The LES model results are of variable quality and do not provide a consistent baseline against which to compare the NWP models, particularly under high aerosol or cloud droplet number concentration (CDNC) conditions. The main SCM bias appears to be toward the overdevelopment of fog, i.e. fog which is too thick, although the inter-model variability is large. In reality there is a subtle balance between water lost to the surface and water condensed into fog, and the ability of a model to accurately simulate this process strongly determines the quality of its forecast. Some NWP SCMs do not represent fundamental components of this process (e.g. cloud droplet sedimentation) and therefore are naturally hampered in their ability to deliver accurate simulations. Finally, we show that modelled fog development is as sensitive to the shape of the cloud droplet size distribution, a rarely studied or modified part of the microphysical parameterisation, as it is to the underlying aerosol or CDNC.

scholarly journals Demistify: an LES and SCM intercomparison of radiation fog

2021 ◽  
Author(s):  
Ian Boutle ◽  
Wayne Angevine ◽  
Jian-Wen Bao ◽  
Thierry Bergot ◽  
Ritthik Bhattacharya ◽  
...  
Keyword(s):  
Weather Prediction ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Radiation Fog ◽  
Eddy Simulation ◽  
Cloud Droplet Size Distribution ◽  
Single Column ◽  
Research Grade ◽  
Model Variability ◽  
Les Model

Abstract. An intercomparison between 10 single-column (SCM) and 5 large-eddy simulation (LES) models is presented for a radiation fog case study inspired by the LANFEX field campaign. 7 of the SCMs represent single-column equivalents of operational numerical weather prediction (NWP) models, whilst 3 are research-grade SCMs designed for fog simulation, and the LES are designed to reproduce in the best manner currently possible the underlying physical processes governing fog formation. The LES model results are of variable quality, and do not provide a consistent baseline against which to compare the NWP models, particularly under high aerosol or cloud droplet number (CDNC) conditions. The main SCM bias appears to be toward over-development of fog, i.e. fog which is too thick, although the inter-model variability is large. In reality there is a subtle balance between water lost to the surface and water condensed into fog, and the ability of a model to accurately simulate this process strongly determines the quality of its forecast. Some NWP-SCMs do not represent fundamental components of this process (e.g. cloud droplet sedimentation) and therefore are naturally hampered in their ability to deliver accurate simulations. Finally, we show that modelled fog development is as sensitive to the shape of the cloud droplet size distribution, a rarely studied or modified part of the microphysical parametrization, as it is to the underlying aerosol or CDNC.

The Germano Large Eddy Simulation Model Used for the Simulation of Separated Flow

2003 ◽  
Author(s):  
Engin Cetindogan ◽  
Govert de With ◽  
Arne E. Holdo̸
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Computational Study ◽  
Separated Flow ◽  
Local Flow ◽  
Large Eddy Simulation Model ◽  
Slip Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

A computational study of unsteady, separated fluid flow was made using the Large Eddy Simulation (LES). As flow problem the turbulent flow past a circular cylinder at a Reynolds number of Re = 3900 was chosen. The objective of this work was to study the numerical and modelling aspects of the dynamic Germano-LES turbulence model. Before LES can be used for applications of practical relevance, such as the flow around a complete aircraft or automobile, extensive tests must be carried out on simpler configurations to understand the quality of LES. Also, the influence of different grid resolutions was examined. Due to the fact of a low Reynolds number, no-slip boundary conditions were used at solid walls. Two different subgrid scale models were applied. In recent years several simulations were carried out using the Smagorinsky-LES model but there is still a lack of experience using the dynamic Germano-LES model, which takes the local flow parameters into account. Several simulations with different parameters and grid-models were carried out both with the Germano-LES model and the Smagorinsky-LES model. Comparisons were made between these two models as well as with several experimental data taken from literature.

scholarly journals Large-eddy simulation of plume dispersion under various thermally stratified boundary layers

2014 ◽  
Vol 11 (1) ◽  
pp. 75-81 ◽  
Author(s):  
H. Nakayama ◽  
T. Takemi ◽  
H. Nagai
Keyword(s):  
Large Eddy Simulation ◽  
Boundary Layers ◽  
Atmospheric Stability ◽  
Spanwise Direction ◽  
Plume Dispersion ◽  
Convective Boundary ◽  
Gas Dispersion ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Abstract. Contaminant gas dispersion in atmospheric boundary layer is of great concern to public health. For the accurate prediction of the dispersion problem, the present study numerically investigates the behavior of plume dispersion by taking into account the atmospheric stability which is classified into three types; neutral, stable, and convective boundary layers. We first proposed an efficient method to generate spatially-developing, thermally-stratified boundary layers and examined the usefulness of our approach by comparing to wind tunnel experimental data for various thermal boundary layers. The spreads of plume in the spanwise direction are quantitatively underestimated especially at large downwind distances from the point source, owing to the underestimation of turbulence intensities for the spanwise component; however, the dependence of the spanwise spreads to atmospheric stability is well represented in a qualitative sense. It was shown that the large-eddy simulation (LES) model provides physically reasonable results.

scholarly journals Implementing Large-Eddy Simulation Capability in a Compressible Mesoscale Model

2014 ◽  
Vol 142 (8) ◽  
pp. 2733-2750 ◽  
Author(s):  
Nicolas Gasset ◽  
Robert Benoit ◽  
Christian Masson
Keyword(s):  
Large Eddy Simulation ◽  
Mesoscale Model ◽  
Wind Farms ◽  
Test Cases ◽  
Eddy Simulation ◽  
Large Size ◽  
Large Eddy ◽  
Vertical Turbulence ◽  
Les Model ◽  
Future Work

Abstract The large size of modern wind turbines and wind farms triggers processes above the surface layer, which extend to the junction between microscales and mesoscales, and pushes the limits of existing approaches to predict the wind. The main objectives of this study are thus to introduce and evaluate an approach that will better account for physical processes within the atmospheric boundary layer (ABL), and allow for both microscale and mesoscale modeling. The proposed method, in which mathematical model and main numerical aspects are presented, combines a mesoscale approach with a large-eddy simulation (LES) model based on the Compressible Community Mesoscale Model (MC2). It is evaluated relying on a shear-driven ABL case allowing the authors to assess the model behavior at very high resolution as well as more specific numerical aspects such as the vertical discretization and time and space splitting of turbulence-related terms. The proposed LES-capable mesoscale model is shown to perform on par with other similar reference LES models, while being slightly more dissipative. A new vertical discretization of the turbulent processes eliminates a spurious numerical mode in the solution. Finally, the splitting of horizontal and vertical turbulence-related terms is shown to have no impact on the results of the test cases. It is thus demonstrated that the revised MC2 is suitable at both microscales and mesoscales, thus setting a strong foundation for future work.

scholarly journals UCLALES–SALSA v1.0: a large-eddy model with interactive sectional microphysics for aerosol, clouds and precipitation

2017 ◽  
Vol 10 (1) ◽  
pp. 169-188 ◽  
Author(s):  
Juha Tonttila ◽  
Zubair Maalick ◽  
Tomi Raatikainen ◽  
Harri Kokkola ◽  
Thomas Kühn ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Aerosol Size Distribution ◽  
Physical Processes ◽  
Radiation Fog ◽  
Marine Stratocumulus ◽  
Aerosol Cloud ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wet Scavenging

Abstract. Challenges in understanding the aerosol–cloud interactions and their impacts on global climate highlight the need for improved knowledge of the underlying physical processes and feedbacks as well as their interactions with cloud and boundary layer dynamics. To pursue this goal, increasingly sophisticated cloud-scale models are needed to complement the limited supply of observations of the interactions between aerosols and clouds. For this purpose, a new large-eddy simulation (LES) model, coupled with an interactive sectional description for aerosols and clouds, is introduced. The new model builds and extends upon the well-characterized UCLA Large-Eddy Simulation Code (UCLALES) and the Sectional Aerosol module for Large-Scale Applications (SALSA), hereafter denoted as UCLALES-SALSA. Novel strategies for the aerosol, cloud and precipitation bin discretisation are presented. These enable tracking the effects of cloud processing and wet scavenging on the aerosol size distribution as accurately as possible, while keeping the computational cost of the model as low as possible. The model is tested with two different simulation set-ups: a marine stratocumulus case in the DYCOMS-II campaign and another case focusing on the formation and evolution of a nocturnal radiation fog. It is shown that, in both cases, the size-resolved interactions between aerosols and clouds have a critical influence on the dynamics of the boundary layer. The results demonstrate the importance of accurately representing the wet scavenging of aerosol in the model. Specifically, in a case with marine stratocumulus, precipitation and the subsequent removal of cloud activating particles lead to thinning of the cloud deck and the formation of a decoupled boundary layer structure. In radiation fog, the growth and sedimentation of droplets strongly affect their radiative properties, which in turn drive new droplet formation. The size-resolved diagnostics provided by the model enable investigations of these issues with high detail. It is also shown that the results remain consistent with UCLALES (without SALSA) in cases where the dominating physical processes remain well represented by both models.

Large-Eddy Simulation of Marine Atmospheric Boundary Layers above a Spectrum of Moving Waves

2014 ◽  
Vol 71 (11) ◽  
pp. 4001-4027 ◽  
Author(s):  
Peter P. Sullivan ◽  
James C. McWilliams ◽  
Edward G. Patton
Keyword(s):  
Large Eddy Simulation ◽  
Wind Wave ◽  
Small Scale ◽  
Time Varying ◽  
Wave Age ◽  
Near Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wave Induced ◽  
Les Model

Abstract Momentum and scalar transport in the marine atmospheric boundary layer (MABL) is driven by a turbulent mix of winds, buoyancy, and surface gravity waves. To investigate the interaction between these processes, a large-eddy simulation (LES) model is developed with the capability to impose a broadband spectrum of time-varying finite-amplitude surface waves at its lower boundary. The LES model adopts a Boussinesq flow model and integrates the governing equations on a time-varying, surface-fitted, nonorthogonal mesh using cell-centered variables with special attention paid to the solution of the pressure Poisson equation near the wavy boundary. Weakly unstable MABLs are simulated with geostrophic winds increasing from 5 to 25 m s−1 and wave age varying from swell-dominated to wind-wave equilibrium. The simulations illustrate cross-scale coupling as wave-impacted near-surface turbulence transitions into shear-convective rolls with increasing distance from the water. In a regime with swell, low winds, and weak heating, wave-induced vertical velocity and pressure signals are readily observed well above the standard reference height ζa = 10 m. At wind-wave equilibrium, the small-scale wave-induced signals are detectable only near the water surface. Below ζa, a nearly-constant-flux layer is observed where the momentum flux carried by turbulence, form stress, and subgrid-scale motions shifts with varying wave age and distance above the water. The spectral content of the surface form stress is wave-age dependent, especially at low wavenumbers. The LES wind profiles deviate from Monin–Obukhov similarity theory in nonequilibrium wind-wave conditions, and entrainment is greatly enhanced by shear-induced engulfment events.

Large Eddy Simulation of Aerodynamic Forces on a Bridge Pylon

2011 ◽  
Vol 243-249 ◽  
pp. 1578-1582
Author(s):  
Xu Yong Ying ◽  
Fu You Xu ◽  
Zhe Zhang ◽  
Yong Gang Tan
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Wind Tunnel Test ◽  
Navier Stokes ◽  
Aerodynamic Forces ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

In this study, aerodynamic forces on a bridge pylon are investigated by three-dimensional computational fluid dynamics using Large eddy simulation (LES) technology. The main objective is to identify the wind load parameters of the pylon and examine the accuracy of LES model applied to the bluff-body flows. The numerical results were compared with the available wind tunnel test results. Also, a comparison between using LES and Reynolds averaged Navier-Stokes equations with the RNG model have been made. It is found that the LES model competes the RNG model in accuracy for predictions of aerodynamic forces on the pylon.

scholarly journals Large Eddy Simulation of Microphysics and Influencing Factors in Shallow Convective Clouds

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 485
Author(s):  
Zhuangzhuang Zhou ◽  
Chongzhi Yin ◽  
Chunsong Lu ◽  
Xingcan Jia ◽  
Fang Ye ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Influencing Factors ◽  
Vertical Velocity ◽  
Large Scale ◽  
Cloud Droplet ◽  
Relative Dispersion ◽  
Cloud Base ◽  
Convective Clouds ◽  
Eddy Simulation ◽  
Large Eddy

A flight of shallow convective clouds during the SCMS95 (Small Cumulus Microphysics Study 1995) observation project is simulated by the large eddy simulation (LES) version of the Weather Research and Forecasting Model (WRF-LES) with spectral bin microphysics (SBM). This study focuses on relative dispersion of cloud droplet size distributions, since its influencing factors are still unclear. After validation of the simulation by aircraft observations, the factors affecting relative dispersion are analyzed. It is found that the relationships between relative dispersion and vertical velocity, and between relative dispersion and adiabatic fraction are both negative. Furthermore, the negative relationships are relatively weak near the cloud base, strengthen with the increasing height first and then weaken again, which is related to the interplays among activation, condensation and evaporation for different vertical velocity and entrainment conditions. The results will be helpful to improve parameterizations related to relative dispersion (e.g., autoconversion and effective radius) in large-scale models.

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