scholarly journals Explaining the convector effect in canopy turbulence by means of large-eddy simulation

2017 ◽  
Vol 21 (6) ◽  
pp. 2987-3000 ◽  
Author(s):  
Tirtha Banerjee ◽  
Frederik De Roo ◽  
Matthias Mauder
Keyword(s):  
Aerodynamic Resistance ◽  
Sensible Heat Flux ◽  
Canopy Turbulence ◽  
Large Eddy Simulations ◽  
General Description ◽  
Sensible Heat ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Aerodynamic Roughness ◽  
Resistance To Heat

Abstract. Semi-arid forests are found to sustain a massive sensible heat flux in spite of having a low surface to air temperature difference by lowering the aerodynamic resistance to heat transfer (rH) – a property called the canopy convector effect (CCE). In this work large-eddy simulations are used to demonstrate that the CCE appears more generally in canopy turbulence. It is indeed a generic feature of canopy turbulence: rH of a canopy is found to reduce with increasing unstable stratification, which effectively increases the aerodynamic roughness for the same physical roughness of the canopy. This relation offers a sufficient condition to construct a general description of the CCE. In addition, we review existing parameterizations for rH from the evapotranspiration literature and test to what extent they are able to capture the CCE, thereby exploring the possibility of an improved parameterization.

scholarly journals Explaining the convector effect in canopy turbulence by means of large-eddy simulation

2017 ◽  
Author(s):  
Tirtha Banerjee ◽  
Frederik De Roo ◽  
Matthias Mauder
Keyword(s):  
Aerodynamic Resistance ◽  
Sensible Heat Flux ◽  
Canopy Turbulence ◽  
Large Eddy Simulations ◽  
General Description ◽  
Sensible Heat ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Aerodynamic Roughness ◽  
Resistance To Heat

Abstract. Semi-arid forests are found to sustain a massive sensible heat flux in spite of having a low surface to air temperature difference by lowering the aerodynamic resistance to heat transfer (rH) – a property called canopy convector effect (CCE). In this work large-eddy simulations are used to demonstrate that CCE appears more generally in canopy turbulence. It is indeed a generic feature of canopy turbulence: rH of a canopy is found to reduce with increasing unstable stratification, which effectively increases the aerodynamic roughness for the same physical roughness of the canopy. This relation offers a sufficient condition to construct a general description of CCE. In addition, we review existing parameterizations for rH from the evapotranspiration literature and test to what extent they are able to capture the CCE, thereby exploring the possibility of an improved parameterization.

scholarly journals Significant Decrease of Uncertainties in Sensible Heat Flux Simulation Using Temporally Variable Aerodynamic Roughness in Two Typical Forest Ecosystems of China

2012 ◽  
Vol 51 (6) ◽  
pp. 1099-1110 ◽  
Author(s):  
Yanlian Zhou ◽  
Weimin Ju ◽  
Xiaomin Sun ◽  
Xuefa Wen ◽  
Dexin Guan
Keyword(s):  
Heat Flux ◽  
Roughness Length ◽  
Aerodynamic Resistance ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Sensible Heat ◽  
Atmospheric Stratification ◽  
Thermal Roughness Length ◽  
Aerodynamic Roughness ◽  
Simulation Errors

AbstractAerodynamic roughness length zom is an important parameter for reliably simulating surface fluxes. It varies with wind speed, atmospheric stratification, terrain, and other factors. However, it is usually considered a constant. It is known that uncertainties in zom result in latent heat flux (LE) simulation errors, since zom links LE with aerodynamic resistance. The effects of zom on sensible heat flux (SH) simulation are usually neglected because there is no direct link between the two. By comparing SH simulations with three types of zom inputs, it is found that allowing zom temporal variation in an SH simulation model significantly improves agreement between simulated and measured SH and also decreases the sensitivity of the SH model to the heat transfer coefficient Ct, which in turn determines the linkage between zom and thermal roughness length zoh.

scholarly journals THERMAL LARGE EDDY SIMULATION WITH SENSIBLE HEAT FLUX DISTRIBUTION FROM VARIOUS 3D BUILDING GEOMETRIES

2015 ◽  
Vol 71 (4) ◽  
pp. I_433-I_438 ◽  
Author(s):  
Mohammed BAKKALI ◽  
Atsushi INAGAKI ◽  
Yasunobu ASHIE ◽  
Yuma YOSHIDA ◽  
Manabu KANDA ◽  
...  
Keyword(s):  
Heat Flux ◽  
Large Eddy Simulation ◽  
Flux Distribution ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Heat Flux Distribution ◽  
Eddy Simulation ◽  
Large Eddy

Large-Eddy Simulation of Roughened NACA65 Compressor Cascade

2017 ◽  
Author(s):  
Jongwook Joo ◽  
Gorazd Medic ◽  
Om Sharma
Keyword(s):  
Surface Roughness ◽  
Large Eddy Simulations ◽  
Surface Imaging ◽  
Potential Solution ◽  
Discrete Elements ◽  
Compressor Cascade ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Modeling ◽  
The One

Large eddy simulations over a NACA65 compressor cascade with roughness were performed for multiple roughness heights. The experiments show flow separation as airfoil roughness is increased. In LES computations, surface roughness was represented by regularly arranged discrete elements using guidelines from Schlichting. Results from wall-resolved LES indicate that specifying an equivalent sandgrain roughness height larger than the one in experiments is required to reproduce the same effects observed in experiments. This highlights the persisting uncertainty with matching the experimental roughness geometry in LES computations, pointing towards surface imaging and digitization as a potential solution. Some initial analysis of flow physics has been conducted with the aim of guiding the RANS modeling for roughness.

Reliable and Accurate Prediction of Three-Dimensional Separation in Asymmetric Diffusers Using Large-Eddy Simulation

2009 ◽  
Author(s):  
Hayder Schneider ◽  
Dominic von Terzi ◽  
Hans-Jo¨rg Bauer ◽  
Wolfgang Rodi
Keyword(s):  
Experimental Data ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

Reynolds-Averaged Navier-Stokes (RANS) calculations and Large-Eddy Simulations (LES) of the flow in two asymmetric three-dimensional diffusers were performed. The numerical setup was chosen to be in compliance with previous experiments. The aim of the present study is to find the least expensive method to compute reliably and accurately the impact of geometric sensitivity on the flow. RANS calculations fail to predict both the extent and location of the three-dimensional separation bubble. In contrast, LES is able to determine the amount of reverse flow and the pressure coefficient within the accuracy of experimental data.

scholarly journals Atmospheric Stability Influences on Coupled Boundary Layer and Canopy Turbulence

2016 ◽  
Vol 73 (4) ◽  
pp. 1621-1647 ◽  
Author(s):  
Edward G. Patton ◽  
Peter P. Sullivan ◽  
Roger H. Shaw ◽  
John J. Finnigan ◽  
Jeffrey C. Weil
Keyword(s):  
Boundary Layer ◽  
Atmospheric Stability ◽  
Canopy Turbulence ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Atmospheric Boundary Layers ◽  
Eddy Simulation ◽  
Scalar Fluxes ◽  
Large Eddy ◽  
Scale Structures

Abstract Large-eddy simulation of atmospheric boundary layers interacting with a coupled and resolved plant canopy reveals the influence of atmospheric stability variations from neutral to free convection on canopy turbulence. The design and implementation of a new multilevel canopy model is presented. Instantaneous fields from the simulations show that organized motions on the scale of the atmospheric boundary layer (ABL) depth bring high momentum down to canopy top, locally modulating the vertical shear of the horizontal wind. The evolution of these ABL-scale structures with increasing instability and their impact on vertical profiles of turbulence moments and integral length scales within and above the canopy are discussed. Linkages between atmospheric turbulence and biological control impact horizontal scalar source distributions. Decreasing spatial correlation between momentum and scalar fluxes with increasing instability results from ABL-scale structures spatially segregating momentum and scalar exchange at canopy top. In combination, these results suggest the need for roughness sublayer parameterizations to incorporate an additional length or time scale reflecting the influence of ABL-scale organized motions.

Comparison of Partially Averaged Navier–Stokes and Large-Eddy Simulations of the Flow Around a Cuboid Influenced by Crosswind

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Siniša Krajnović ◽  
Per Ringqvist ◽  
Branislav Basara
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Better Than ◽  
Good Agreement ◽  
Near Wall

The paper presents a partially averaged Navier–Stokes (PANS) simulation of the flow around a cuboid influenced by crosswind. The results of the PANS prediction are validated against experimental data and results of a large-eddy simulation (LES) made using the same numerical conditions as PANS. The PANS shows good agreement with the experimental data. The prediction of PANS was found to be better than that of the LES in flow regions where simulations suffered from poor near-wall resolution.

Is the water vapor supersaturation distribution Gaussian?

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.

Large Eddy Simulations of Flow past a Circular Cylinder with/without an Upper Rivulet

2011 ◽  
Vol 90-93 ◽  
pp. 851-856
Author(s):  
Xiao Qing Du ◽  
Yan Zhao
Keyword(s):  
Circular Cylinder ◽  
Large Eddy Simulations ◽  
Wind Pressure ◽  
Wake Flow ◽  
Cable Model ◽  
Flow Zone ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Small Vortex ◽  
Fluctuating Wind

Large eddy simulation (LES) is utilized to simulate flow around a circular cylinder with/without an upper rivulet at Reynolds number 70000. Mean and fluctuating wind pressure coefficients on the artificial upper rivulet and the circular cylinder are obtained. The flow field and the vorticity magnitude in the wake flow zone of the cable model with rivulet at different positions were also investigated. It is found that a small vortex occur near the back of rivulet, when it locates in some particular positions, that might be the reason aerodynamic forces changing dramatically. These results lay foundation for the research on regulation about the influence of rivulet size and shape on cable aerodynamic in future.

Stochastic backscatter in large-eddy simulations of boundary layers

1992 ◽  
Vol 242 ◽  
pp. 51-78 ◽  
Author(s):  
P. J. Mason ◽  
D. J. Thomson
Keyword(s):  
Large Scale ◽  
Flow Simulation ◽  
Surface Region ◽  
Large Eddy Simulations ◽  
Flow Profile ◽  
Mean Velocity ◽  
Near Surface ◽  
Eddy Simulation ◽  
Subgrid Model ◽  
Large Eddy

The ability of a large-eddy simulation to represent the large-scale motions in the interior of a turbulent flow is well established. However, concerns remain for the behaviour close to rigid surfaces where, with the exception of low-Reynolds-number flows, the large-eddy description must be matched to some description of the flow in which all except the larger-scale ‘inactive’ motions are averaged. The performance of large-eddy simulations in this near-surface region is investigated and it is pointed out that in previous simulations the mean velocity profile in the matching region has not had a logarithmic form. A number of new simulations are conducted with the Smagorinsky (1963) subgrid model. These also show departures from the logarithmic profile and suggest that it may not be possible to eliminate the error by adjustments of the subgrid lengthscale. An obvious defect of the Smagorinsky model is its failure to represent stochastic subgrid stress variations. It is shown that inclusion of these variations leads to a marked improvement in the near-wall flow simulation. The constant of proportionality between the magnitude of the fluctuations in stress and the Smagorinsky stresses has been empirically determined to give an accurate logarithmic flow profile. This value provides an energy backscatter rate slightly larger than the dissipation rate and equal to idealized theoretical predictions (Chasnov 1991).

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