Environmental Fluid Mechanics

Das, Arghyadip; Dalui, Sujit Kumar

2025 Environmental Fluid Mechanics

doi: 10.1007/s10652-025-10050-4

The present study is carried out to find the influence of various composite geometrical configurations along the height of a corner recessed square tall building considering wind flow around the buildings from 0 to 90° due to the symmetry in both plan axes. A series of numerical analyses have been performed using Computational Fluid Dynamics in the ANSYS-FLUENT module to find the mean pressure coefficient at various building faces. Two orthogonal wind force components (along and across directions) are evaluated using LES turbulence model. The length scale is considered 1:300 for preparing different building models. The modelling of dynamic wind forces has been carried out in SAP2000 to investigate the power spectral density of displacements and accelerations in along and across-wind directions. The results are presented graphically and validated against international standards and previously published literature. The investigation reveals that corner recessing in square tall buildings significantly reduces wind-induced responses such as displacements and accelerations, which are critical for occupant comfort.

Rastello, Marie; Marié, Jean-Louis; Collin, Brivaël; Bellot, Hervé; Naaim, Florence

2025 Environmental Fluid Mechanics

doi: 10.1007/s10652-025-10049-x

The aim of the study is to carry out two-phase gravity driven flows of large light particles on submerged steep slopes and, from their characteristics, identify the criteria that govern the transition between a purely dense and a mixed (dense-suspended) regime. For that, volumes of large light particles are released without any initial velocity at the top of a 2D flume immersed in a 20 m3 tank filled with tap water. The particles are spherical, monodisperse, with two different diameters: 10.6 and 14.4 mm. The volume expansion β, the height H and the front velocity \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$U_f$$\end{document} of the heavy flows are investigated varying the volume released between 0.2 and 3 L, and the tilt angle of the flume (θ) between 30 and 60°. Two different regimes are observed, one where all the particles move in close contact with each other (dense regime), and as the volume and/or flume angle increases, another where part of the particles are suspended (mixed regime). We find that the overall dynamics of the flow is governed by a buoyancy/drag equilibrium ruled by the densimetric Froude number \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$Fr=U_f/\sqrt{(\Delta \rho g/\rho _w) H}$$\end{document}, with g the gravity acceleration and \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\Delta \rho =\rho -\rho _w$$\end{document}. \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\rho $$\end{document} is the density of the flow and \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\rho _w$$\end{document} that of the ambient fluid: water. The corresponding drag coefficient exerted on the particles volume is found to vary as \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$C_d\approx 2{Fr^{-1.6}}$$\end{document}. The key parameter for the onset of the flow of some of the particles in suspension and the transition to the mixed regime proves to be \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$St_\theta =St\cos \theta /(1-St\sin \theta )$$\end{document}, with \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$St=v_s/U_f$$\end{document} the Stokes number comparing the settling velocity of the particles to the flow front velocity. While pressure remains hydrostatic within the flow in the dense regime (\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$St_\theta >0.9$$\end{document}), it increases as suspension occurs in the mixed case and \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$St_\theta $$\end{document} decreases. The dynamic pressure at the forehead of the volume then evolves as \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$ P_{s} \approx \Delta \rho gH\cos (\theta )(1.9 - St_{\theta } )^{2} $$\end{document}.

Sin, Chung Hyok; Cui, Peng-Yi; Zhang, Jia-Ni; Wang, Ke-xin; Luo, Yang; Huang, Yuan-dong

2025 Environmental Fluid Mechanics

doi: 10.1007/s10652-025-10051-3

This study examines the effect of wind catchers (WC) on airflow and pollutant dispersion in a street canyon using a validated numerical model based on wind tunnel data. Both low-rise (H/W = 1) and high-rise (H/W = 2) canyons with a length-to-height ratio of 10 and wind catchers covering the entire roof of the upwind building are simulated, taking into account various structural parameters of the wind catchers. The findings emphasize the key role of wind catcher inlet height in influencing induced flow and suggest that wind catchers are more effective in high-rise than low-rise canyons. In both settings, taller inlet heights significantly enhance the net escape velocity (NEV*). The WCs with a low inlet height (a = H /12) are ineffective for diluting traffic pollutants at the pedestrian respiration planes and on the canyon walls. Additionally, introducing a wind catcher with a high inlet height (a = H/6) and increasing the outlet width (c) significantly enhances the NEV*, while the vertical length of the WC (b) has only a negligible impact on the NEV*. Moreover, when a WC with a high inlet height is utilized, pollutant concentrations at the canyon walls and pedestrian respiration planes are minimally affected by variations in the vertical length and outlet width of the wind catcher. Optimal structural parameters are identified for both low-rise and high-rise canyons to minimize pollutant exposure risks.Graphical abstract[graphic not available: see fulltext]This study examines the influence of the structural parameters of wind catchers on airflow and pollutant dispersion within street canyons. It identifies effective design parameters that can significantly reduce pollutant concentrations in both low-rise and high-rise canyons.