scholarly journals Numerical and Wind Tunnel Simulation Studies of the Flow Field and Pollutant Diffusion around a Building under Neutral and Stable Atmospheric Stratifications

2019 ◽  
Vol 58 (11) ◽  
pp. 2405-2420
Author(s):  
Dong-Peng Guo ◽  
Peng Zhao ◽  
Ren-Tai Yao ◽  
Yun-Peng Li ◽  
Ji-Min Hu ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Vertical Direction ◽  
Lateral Spread ◽  
Atmospheric Stratification ◽  
Stable Conditions ◽  
Horizontal Spread ◽  
Neutral Conditions ◽  
Separation Zones

AbstractIn this paper, the k–ε renormalization group (RNG) turbulence model is used to simulate the flow and dispersion of pollutants emitted from a source at the top of a cubic building under neutral and stable atmospheric stratifications, the results of which were compared with corresponding wind tunnel experiment results. When atmosphere stratification is stable, the separation zones on the sides and at the top of a building are relatively smaller than those under neutral conditions, and the effect of the building in the horizontal direction is stronger than that in the vertical direction. The variation in turbulent kinetic energy under stable conditions is significantly lower than that under neutral conditions. The effect of atmospheric stratification on the turbulent kinetic energy becomes gradually more prominent with increased distance. When atmosphere conditions are stable, the vertical distribution of the plume is smaller than that of neutral conditions, but the lateral spread and near-ground concentration are slightly larger than those of neutral conditions, mainly because stable atmospheric stratification suppresses the vertical motions of airflow and increases the horizontal spread of the plume.

Simulation of a propelled wake with moderate excess momentum in a stratified fluid

2011 ◽  
Vol 692 ◽  
pp. 28-52 ◽  
Author(s):  
Matthew B. de Stadler ◽  
Sutanu Sarkar
Keyword(s):  
Kinetic Energy ◽  
Velocity Profile ◽  
Turbulent Kinetic Energy ◽  
Vertical Direction ◽  
Qualitative Change ◽  
Stratified Fluid ◽  
Mean Velocity ◽  
Moderate Amount ◽  
Excess Momentum ◽  
The Mean

AbstractDirect numerical simulation is used to simulate the turbulent wake behind an accelerating axisymmetric self-propelled body in a stratified fluid. Acceleration is modelled by adding a velocity profile corresponding to net thrust to a self-propelled velocity profile resulting in a wake with excess momentum. The effect of a small to moderate amount of excess momentum on the initially momentumless self-propelled wake is investigated to evaluate if the addition of excess momentum leads to a large qualitative change in wake dynamics. Both the amount and shape of excess momentum are varied. Increasing the amount of excess momentum and/or decreasing the radial extent of excess momentum was found to increase the defect velocity, mean kinetic energy, shear in the velocity gradient and the wake width. The increased shear in the mean profile resulted in increased production of turbulent kinetic energy leading to an increase in turbulent kinetic energy and its dissipation. Slightly larger vorticity structures were observed in the late wake with excess momentum although the differences between vorticity structures in the self-propelled and 40 % excess momentum cases was significantly smaller than suggested by previous experiments. Buoyancy was found to preserve the doubly inflected velocity profile in the vertical direction, and similarity for the mean velocity and turbulent kinetic energy was found to occur in both horizontal and vertical directions. While quantitative differences were observed between cases with and without excess momentum, qualitatively similar evolution was found to occur.

scholarly journals A Diagnosis of Excessive Mixing in Smagorinsky Subfilter-Scale Turbulent Kinetic Energy Models

2017 ◽  
Vol 74 (5) ◽  
pp. 1495-1511 ◽  
Author(s):  
Stephan R. de Roode ◽  
Harm J. J. Jonker ◽  
Bas J. H. van de Wiel ◽  
Victor Vertregt ◽  
Vincent Perrin
Keyword(s):  
Kinetic Energy ◽  
Prandtl Number ◽  
Turbulent Kinetic Energy ◽  
Prediction Models ◽  
Weather Prediction ◽  
Small Scale ◽  
Constant Length ◽  
Similarity Relations ◽  
Stable Conditions ◽  
Mixing Functions

Abstract Large-eddy simulation (LES) models are widely used to study atmospheric turbulence. The effects of small-scale motions that cannot be resolved need to be modeled by a subfilter-scale (SFS) model. The SFS contribution to the turbulent fluxes is typically significant in the surface layer. This study presents analytical solutions of the classical Smagorinsky SFS turbulent kinetic energy (TKE) model including a buoyancy flux contribution. Both a constant length scale and a stability-dependent one as proposed by Deardorff are considered. Analytical expressions for the mixing functions are derived and Monin–Obukhov similarity relations that are implicitly imposed by the SFS TKE model are diagnosed. For neutral and weakly stable conditions, observations indicate that the turbulent Prandtl number (PrT) is close to unity. However, based on observations in the convective boundary layer, a lower value for PrT is often applied in LES models. As a lower Prandtl number promotes a stronger mixing of heat, this may cause excessive mixing, which is quantified from a direct comparison of the mixing function as imposed by the SFS TKE model with empirical fits from field observations. For a strong stability, the diagnosed mixing functions for both momentum and heat are larger than observed. The problem of excessive mixing will be enhanced for anisotropic grids. The findings are also relevant for high-resolution numerical weather prediction models that use a Smagorinsky-type TKE closure.

The Budget of Turbulent Kinetic Energy during Premonsoon Season over Kharagpur as Revealed by STORM Experimental Data

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Bhishma Tyagi ◽  
A. N. V. Satyanarayana
Keyword(s):  
Experimental Data ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Atmospheric Stability ◽  
Regional Modeling ◽  
Severe Thunderstorms ◽  
Dissipation Rates ◽  
Turbulence Data ◽  
Neutral Conditions ◽  
Tropical Station

Turbulent kinetic energy (TKE) budget variations during thunderstorm days (TD) and nonthunderstorm days (NTD) of premonsoon seasons of 2007, 2009, and 2010 have been investigated at a tropical station Kharagpur (22°30′N, 87°20′E) using the surface layer turbulence data obtained during severe thunderstorms-observations and regional modeling (STORM) experiment. Significant variations in the contributions of the TKE budget parameters with respect to stability are observed on these contrasting days of weather activity. In highly unstable conditions, smaller dissipation rates are seen on TD compared to NTD, while approaching near neutral conditions, higher dissipation rates are found in TD. New relationships between TKE dissipation rates with respect to atmospheric stability are proposed at Kharagpur for TD and NTD.

scholarly journals Turbulent kinetic energy budgets in a model canopy: comparisons between LES and wind-tunnel experiments

2008 ◽  
Vol 8 (1) ◽  
pp. 73-95 ◽  
Author(s):  
Wusi Yue ◽  
Charles Meneveau ◽  
Marc B. Parlange ◽  
Weihong Zhu ◽  
Hyung Suk Kang ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Budgets ◽  
Wind Tunnel Experiments

scholarly journals Numerical Simulation of the Flow Field and Pollutant Dispersion around a Hill under Different Thermal Stratifications

2020 ◽  
Vol 59 (1) ◽  
pp. 47-64
Author(s):  
Dong-Peng Guo ◽  
Peng Zhao ◽  
Ran Wan ◽  
Ren-Tai Yao ◽  
Ji-Min Hu
Keyword(s):  
Flow Field ◽  
Pollutant Dispersion ◽  
Windward Side ◽  
Wake Region ◽  
High Concentration ◽  
Atmospheric Stratification ◽  
Stable Conditions ◽  
Structure Of Flow ◽  
The Hill ◽  
Neutral Conditions

AbstractThis paper applied a commercial computational fluid dynamics code, STAR-CD, with the renormalization group k–ε turbulence model to simulate the flow and dispersion of contaminants released from a source on the windward side of a hill under different thermal stratifications. In the wake region, the influence of atmospheric stratification on the flow field is inconspicuous under neutral and unstable conditions because of the effect of mechanical disturbance. However, this influence becomes slightly conspicuous under stable conditions. When atmospheric stratification is stable, in the range of z/H < 1.0 (where z is height above the surface and H is height of the hill), the velocity deficits are smaller than those under neutral and unstable conditions. The maximum turbulence kinetic energy (TKE) appears in the wake regions, and the variation in TKE is significantly lower than that under neutral and unstable conditions. When atmospheric stratification is unstable, the vertical and horizontal spread of the plume is slightly greater than that under neutral and stable conditions and the maximum concentration is less than that under neutral conditions. When the Froude number is large (~11; Brunt–Väisälä frequency = 0.52), atmospheric stratification is slightly stable, the structure of flow around the hill is generally similar to that under neutral conditions, and the high-concentration regions are large on the windward side of the hill. Smaller high-concentration regions just appear on the windward side of the hill under unstable conditions. The pollutant concentrations in the wake region of the hill increase as a result of the effect of thermal stability, and the vertical spreading range of the plume along the downwind axis (x axis) is larger than that under neutral and stable conditions.

Estimates of turbulent kinetic energy dissipation rate for a stratified flow in a wind tunnel

2015 ◽  
Vol 431 ◽  
pp. 175-187 ◽  
Author(s):  
Franciano Scremin Puhales ◽  
Giuliano Demarco ◽  
Luis Gustavo Nogueira Martins ◽  
Otávio Costa Acevedo ◽  
Gervásio Annes Degrazia ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Wind Tunnel ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dissipation Rate ◽  
Stratified Flow ◽  
Energy Dissipation Rate

Probability law of turbulent kinetic energy in the atmospheric surface layer

2021 ◽  
Vol 6 (7) ◽  
Author(s):  
Mohammad Allouche ◽  
Gabriel G. Katul ◽  
Jose D. Fuentes ◽  
Elie Bou-Zeid
Keyword(s):  
Surface Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Atmospheric Surface Layer
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