scholarly journals Assessing the Horizontal Homogeneity of the Atmospheric Boundary Layer (HHABL) Profile Using Different CFD Software

Atmosphere ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 1138
Author(s):  
Islam Abohela ◽  
Elsa Aristodemou ◽  
Abas Hadawey ◽  
Raveendran Sundararajan
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Atmospheric Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Dissipation Rate ◽  
Streamwise Velocity ◽  
Computational Domain ◽  
Wall Function ◽  
Wall Boundary Conditions ◽  
Inlet Conditions

One of the main factors affecting the reliability of computational fluid dynamics (CFD) simulations for the urban environment is the Horizontal Homogeneity of the Atmospheric Boundary Layer (HHABL) profile—meaning the vertical profiles of the mean streamwise velocity, the turbulent kinetic energy, and dissipation rate are maintained throughout the streamwise direction of the computational domain. This paper investigates the preservation of the HHABL profile using three different commercial CFD codes—the ANSYS Fluent, the ANSYS CFD, and the Siemens STAR-CCM+ software. Three different cases were considered, identified by their different inlet conditions for the inlet velocity, turbulent kinetic energy, and dissipation rate profiles. Simulations were carried out using the RANS k-ε turbulence model. Slight variations in the eddy viscosity models, as well as in the wall boundary conditions, were identified in the different software, with the standard wall function with roughness being implemented in the Fluent applications, the scalable wall function with roughness in the CFX applications, and the blended wall function option in the STAR-CCM+ simulations. There was a slight difference in the meshing approach in the three different software, with a prism-layer option in the STAR-CCM+ software, which allowed a finer mesh near the wall/ground boundary. The results show all three software are able to preserve the horizontal homogeneity of the ABL—less than 0.5% difference between the software—indicating very similar degrees of accuracy.

scholarly journals Spatiotemporal Dynamics of the Kinetic Energy in the Atmospheric Boundary Layer from Minisodar Measurements

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 421
Author(s):  
Alexander Potekaev ◽  
Liudmila Shamanaeva ◽  
Valentina Kulagina
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Atmospheric Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Time Of Day ◽  
Linear Increase ◽  
Spatiotemporal Dynamics ◽  
Intermediate Layers ◽  
Subsequent Decrease ◽  
Stable Atmospheric Boundary Layer

Spatiotemporal dynamics of the atmospheric kinetic energy and its components caused by the ordered and turbulent motions of air masses are estimated from minisodar measurements of three velocity vector components and their variances within the lowest 5–200 m layer of the atmosphere, with a particular emphasis on the turbulent kinetic energy. The layered structure of the total atmospheric kinetic energy has been established. From the diurnal hourly dynamics of the altitude profiles of the turbulent kinetic energy (TKE) retrieved from minisodar data, four layers are established by the character of the altitude TKE dependence, namely, the near-ground layer, the surface layer, the layer with a linear TKE increase, and the transitive layer above. In the first layer, the most significant changes of the TKE were observed in the evening hours. In the second layer, no significant changes in the TKE values were observed. A linear increase in the TKE values with altitude was observed in the third layer. In the fourth layer, the TKE slightly increased with altitude and exhibited variations during the entire observation period. The altitudes of the upper boundaries of these layers depended on the time of day. The MKE values were much less than the corresponding TKE values, they did not exceed 50 m2/s2. From two to four MKE layers were distinguished based on the character of its altitude dependence. The two-layer structures were observed in the evening and at night (under conditions of the stable atmospheric boundary layer). In the morning and daytime, the four-layer MKE structures with intermediate layers of linear increase and subsequent decrease in the MKE values were observed. Our estimates demonstrated that the TKE contribution to the total atmospheric kinetic energy considerably (by a factor of 2.5–3) exceeded the corresponding MKE contribution.

Structure of Turbulence Around the Trailing Edge of a Rotor Blade

2007 ◽  
Author(s):  
Francesco Soranna ◽  
Yi-Chih Chow ◽  
Oguz Uzol ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Production Rate ◽  
Rotor Blade ◽  
Streamwise Velocity ◽  
Small Region ◽  
Shear Strain Rate ◽  
Suction Surface ◽  
Trailing Edge

This paper focuses on the structure of turbulence around the trailing edge of a rotor blade operating behind a row of Inlet Guide Vanes (IGVs) located upstream of the rotor. High resolution, two-dimensional Particle Image Velocimetry (PIV) measurements are conducted in a refractive index matched turbomachinery facility that provides unobstructed view of the entire flow field. We focus on a small region around the rotor blade trailing edge, extending from 0.04c upstream of the trailing edge to about 0.1c downstream of it, c being the blade chord length. We examine the phase dependent distribution of turbulent kinetic energy (TKE) and its in-plane components of production rate. Impingement of an IGV wake on the suction surface of a rotor blade, near the trailing edge region, reduces the thickness of the boundary layer within the region impinged by the wake. The resulting increase in phase averaged shear strain rate increases the production rate and causes a striking increase in peak turbulent kinetic energy in the near wake. Streamwise velocity gradients, i.e. compression, also contribute to turbulence production, especially when the boundary layer at trailing edge is relatively thick, i.e. when it is not impinged by the IGV wake.

Numerical simulation of the evening transition in the atmospheric boundary layer using LES and RANS models

2021 ◽  
Author(s):  
Ekaterina Tkachenko ◽  
Andrey Debolskiy ◽  
Evgeny Mortikov
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Kinetic Energy ◽  
Atmospheric Boundary Layer ◽  
Decay Rate ◽  
Surface Heat Flux ◽  
Dissipation Rate ◽  
Surface Heat ◽  
Evening Transition ◽  
Rans Models

<div>This study investigates the dynamics of the evening transition in the atmospheric boundary layer (ABL) diurnal cycle, specifically the decay of the turbulent kinetic energy (TKE) taking place there. Generally, the TKE decay is assumed to follow the power law E(t) ~ t<sup>-α,</sup> where E(t) and t are normalized TKE and normalized time, respectively, and the parameter α determines the decay rate. </div><div> <p>Two types of ABL numerical modeling are compared: three-dimensional large-eddy simulation (LES) models and one-dimensional Reynolds-averaged Navier-Stokes (RANS) models. The evening transition is simulated through facilitating the formation of the convective boundary layer (CBL) by having a constant positive surface heat flux, and the subsequent decay of the CBL when the surface heat flux is decreased. </p> <p>Several features of this process have been studied in relative depth, in particular the TKE decay rate at different stages of the evening transition, the sensitivity of the results to the domain size, and the dynamics of the large- and small-scale turbulence during the transition period. LES experiments with different setups were performed, and the results were then compared to those obtained through RANS experiments based on the k-epsilon model (a two-equation model for TKE and dissipation rate, where model constants are chosen to allow for correct simulation of SBL main properties [1], as well as CBL growth rate [2]).</p> <p>This study was funded by Russian Foundation of Basic Research within the project N 20-05-00776 and the grant of the RF President within the MK-1867.2020.5 project.</p> <div>1. Mortikov E. V., Glazunov A. V., Debolskiy A. V., Lykosov V. N., Zilitinkevich S. S. Modeling of the Dissipation Rate of Turbulent Kinetic Energy // Doklady Earth Sciences. 2019. V. 489(2). P. 1440-1443 </div> <p>2. Burchard H. Applied Turbulence Modelling in Marine Waters. Berlin, Germany: Springer, 2002. P. 57-59</p> </div>

Atmospheric boundary layer turbulence in the presence of swell: turbulent kinetic energy budget, Monin-Obukhov similarity theory and inertial dissipation method

2020 ◽  
Author(s):  
Zhongshui Zou
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Atmospheric Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Similarity Theory ◽  
Turbulent Transport ◽  
Ocean Waves ◽  
Turbulent Stress ◽  
Total Stress ◽  
Inertial Dissipation Method

<p><span>Turbulence over the mobile ocean surface has distinct properties compared to turbulence over land. This raises the issue of whether functions such as the turbulent kinetic energy (TKE) budget and Monin-Obukhov similarity theory (MOST) determined over land are directly applicable to ocean surfaces because of the existence of a wave boundary layer (the lower part of atmospheric boundary layer including effects of surface waves. We used the term “WBL” in this article for convenience), where the total stress can be separated into turbulent stress and wave coherent stress. Here the turbulent stress is defined as the stress generated by wind shear and buoyancy, and wave coherent stress accounts for the momentum transfer between ocean waves and atmosphere. In this study, applications of the turbulent kinetic energy (TKE) budget and the inertial dissipation method (IDM) in the context of the Monin-Obukhov similarity theory (MOST) within the WBL are examined. It was found that turbulent transport terms in the TKE budget should not be neglected when calculating the total stress under swell conditions. This was confirmed by observations made on a fixed platform. The results also suggested that turbulent stress, rather than total stress should be used when applying the MOST within the WBL. By combing the TKE budget and MOST, our study showed that the stress computed by the traditional IDM corresponds to turbulent stress rather than total stress. The swell wave coherent stress should be considered when applying the IDM to calculate the stress in the WBL.</span></p>

scholarly journals Lidar Studies of Wind Turbulence in the Stable Atmospheric Boundary Layer

2018 ◽  
Vol 10 (8) ◽  
pp. 1219 ◽  
Author(s):  
Viktor Banakh ◽  
Igor Smalikho
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Atmospheric Boundary Layer ◽  
Dissipation Rate ◽  
Maximum Velocity ◽  
Turbulent Energy ◽  
Integral Scale ◽  
Stable Atmospheric Boundary Layer ◽  
Low Level Jets ◽  
Vertical Size

The kinetic energy of turbulence, the dissipation rate of turbulent energy, and the integral scale of turbulence in the stable atmospheric boundary layer at the location heights of low-level jets (LLJs) have been measured with a coherent Doppler light detection and ranging (lidar) system. The turbulence is shown to be weak in the central part of LLJs. The kinetic energy of turbulence at the maximum velocity heights of the jet does not exceed 0.1 (m/s)2, while the dissipation rate is about 10−5 m2/s3. On average, the integral scale of turbulence in the central part of the jet is about 100 m, which is two to three times less than the effective vertical size of the LLJ.

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