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The surface-averaged forced Convective Heat Transfer Coefficient (CHTC avg ) at a windward building facade is influenced by the complex interaction between a wide range of parameters. Existing CHTC expressions, however, consider the impact of these parameters either incompletely or not at all. Earlier studies have shown that this shortcoming can lead to significant errors in Building Energy Simulations. In this paper, therefore, the combined impacts of wind speed (U 10 ), building height (H) and width (W), and wind direction (θ) on the CHTC avg for the windward facade of buildings are systematically investigated. High-resolution CFD simulations of wind flow and forced convective heat transfer, validated with wind-tunnel measurements, are performed for 64 building geometries (10 m ≤ H and W ≤ 80 m), 8 wind directions (0° ≤ θ ≤ 78.75°) and 4 reference wind speeds (1 m/s ≤ U 10  ≤ 4 m/s). The 3D steady RANS equations with the realizable k-ε turbulence model and the low-Re number Wolfshtein model are used. The results show that for a given building geometry and U 10 , the CHTC avg decreases as θ increases from 0° to 78.75°. The maximum reduction of about 42% occurs for the building with H = 8W = 80 m. In addition, for a given θ and U 10 , by increasing H, the CHTC avg increases, while increasing W has the opposite impact on the CHTC avg . Finally, a new generalized CHTC expression is presented as a function of U 10 , H, W and θ, and its accuracy is confirmed by detailed in-sample and out-of-sample evaluations. [ABSTRACT FROM AUTHOR]

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Large eddy simulation (LES) is widely used to investigate the aerodynamics and convective heat transfer (CHT) at the surfaces of sharp-edged bluff bodies for a wide range of Reynolds (Re) numbers. Due to the heavy computational costs associated with implicit filtering in LES at high Reynolds number flows (Re ≥ 105), wall-modeled (WM) rather than wall-resolved (WR) LES is often adopted. However, the performance of LES-WM for such applications has not yet been systematically investigated. Therefore, this study evaluates the performance of LES-WM and LES-WR for the flow and thermal field at the facades of a low-rise building immersed in an atmospheric boundary layer. Four grids are constructed for LES-WM, each employing different resolution at the building surfaces reaching maximum non-dimensional wall distance y+ = 43, 57, 70, and 95. In addition, the performance of two wall functions, namely the Werner and Wengle and the enhanced wall function is investigated. The results show that the use of LES-WM can result in significant deviations in the predicted near-facade flow pattern and the surface convective heat transfer coefficient (CHTC). Grid resolution significantly impacts the CHTC results and deviations go up to 88% (at the base of the windward facade). Considerable deviations among the employed wall functions are apparent only on the finest grid. In this case, the implementation of the enhanced wall function indicates better performance compared to the non-blended law of the wall (combined with the Werner and Wengle) for CHTC in the regions of the leeward facade where the flow remains attached to the wall. The deviation of the enhanced wall function for surface-averaged CHTC is found to be 10.8% against the wall-resolved LES results, while for the non-blended law of the wall this is 19.2%. • Comparing wall-resolved and wall-modeled LES for flow and CHTC at building facades. • Wall-modeled LES shows significantly different near-surface flow pattern predictions. • Wall-modeled LES shows up to 88% deviation in local CHTC due to grid resolution. • LES models lead to 60% and 54% deviations in surface- and building-averaged CHTC. [ABSTRACT FROM AUTHOR]

Previous research indicated that the surface-averaged forced convective heat transfer coefficient (CHTC) at a windward building facade can vary substantially as a function of building width and height. However, existing CHTC expressions generally do not consider the building dimensions as parameters and are therefore strictly only applicable for the building geometry for which they were derived. Most CHTC expressions also categorize facades only as either windward or leeward. This indicates the need for new and more generally applicable CHTC expressions. This paper presents new generalized expressions for surface-averaged forced CHTC at building facades and roofs that contain the reference wind speed, the width and the height of the windward building facade as parameters. These expressions are derived from CFD simulations of wind flow and forced convective heat transfer for 81 different isolated buildings. The 3D Reynolds-averaged Navier-Stokes equations are solved with a combination of the high-Re number realizable k-ε model and the low-Re number Wolfshtein model. First, a validation study is performed with wind-tunnel measurements of surface temperature for a reduced-scale cubic model. Next, the actual simulations are performed on a high-resolution grid with a minimum near-wall cell size of 400 μm to resolve the entire boundary layer, including the viscous sublayer and the buffer layer, which dominate the convective surface resistance. The new CHTC expressions are analytical formulae (trivariate polynomials) that can easily be implemented in Building Energy Simulation (BES) and Building Envelope Heat-Air-Moisture (BE-HAM) transfer programs. The accuracy of the expressions is confirmed by in-sample and out-of-sample evaluations. [ABSTRACT FROM AUTHOR]

Generating economical, high-resolution and high-quality computational grids for Large Eddy Simulation (LES) of wind flow and convective heat transfer (CHT) around surface-mounted obstacles is not straightforward. When the grid size is used as filter, LES grids should ideally consist of cubic cells, while CHT requires a very high near-wall resolution to resolve the thin viscous sublayer and buffer layer that represent the largest resistance to CHT. To avoid very high cell numbers and the need for excessive computational resources, non-conformal grids can be considered. This paper provides a detailed evaluation of the performance of non-conformal grids with cubic cells, for wind flow and CHT around a wall-mounted cubic obstacle. LES results on non-conformal versus conformal grids are compared with each other and with wind-tunnel measurements of wind speed and surface temperature. Moreover, sensitivity analysis is performed concerning the impact of overall grid resolution, subdomain size and grid refinement ratio. Average absolute deviations between LES on non-conformal versus conformal grids are about 0.9% (0.5 °C) for surface temperature on all cube surfaces. Comparison with experiments shows for the non-conformal grid an average and maximum absolute deviation for surface temperature of 2.0% (1.1 °C) and 7.6% (3.6 °C), respectively. The sensitivity analysis shows minor impact of subdomain size on convective heat transfer coefficients (CHTC) where, on average, absolute deviations of less than 2.2% are observed. This study shows that non-conformal grids can strongly reduce the total cell count (here by a factor up to 30.2) without significantly compromising the accuracy of results. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D), two-phase numerical model was developed and presented as a useful tool for investigating oxygen bubble propagation in porous transport layers (PTLs) (otherwise known as gas diffusion layers (GDLs)) of polymer electrolyte membrane (PEM) electrolyzers. The volume-of-fluid (VoF) technique was employed to simulate the liquid-gas interface movement through liquid-saturated porous media designed to be representative of PEM electrolyzer PTLs. The circulation of the liquid within the channel and the porous domain was included in the model. Bubble propagation patterns and bulk saturations for porous material representations of commonly used PTLs were determined as a function of time leading up to the moment of breakthrough. Previously conducted experimental microfluidic investigations were used for model validation, and it was found that the numerical results were in good agreement with the numerical predictions. The validated model was used to calculate pressure variations in bubbles during propagation, and the highest threshold capillary pressure corresponding to a critical throat was introduced as a means to measure the efficacy of oxygen bubble removal. The information obtained from the developed numerical tool can be used for designing and evaluating PTL microstructures for next generation electrolyzer materials. [ABSTRACT FROM AUTHOR]

Urokinase plasminogen activator receptor (uPAR) and its ligands play a major role in many tumors by mediating extracellular matrix degradation and signaling cascades leading to tumor growth, invasion and metastasis. Recently we introduced uPAR decapeptide antagonist with cytotoxic effect on MDA-MB-231 cell line. In this study we assessed the alteration in uPAR downstream signaling following treatment with the peptide antagonist. In this regard, extracellular-signal-regulated kinase (ERK) and p38 from mitogenactivated protein kinase family and Bcl-2, Bim and Bax from Bcl-2 protein family were investigated. Our data revealed that the peptide caused p38 activation and low ERK activation. On the other hand, the peptide induced down-regulation of Bcl-2 and up-regulation of Bim without Bax modulation. Changes in target protein expression/activation explain the apoptotic property of the peptide and highlight its potential to be used as a therapeutic agent in cancerous cells expressing high levels of uPAR. [ABSTRACT FROM AUTHOR]

Metamodels are developed and used for aerodynamic optimization of a ducted opening integrated into a high-rise building to maximize the amplification factor within the duct. The duct consists of a nozzle, a throat, and a diffuser. 211 high-resolution 3D RANS CFD simulations are performed to generate training and testing datasets. The space-filling design and Genetic algorithm are used for data sampling and optimization, respectively. The performance of five commonly-used metamodels is systematically investigated: Response Surface Methodology (RSM), Kriging (KG), Neural Network (NN), Support Vector Regression (SVR), and Genetic Aggregation Response Surface (GARS). The investigation is based on (i) detailed in-sample and out-of-sample evaluations of the metamodels, (ii) annual available power in the wind (P available), and (iii) annual energy production (AEP) for a 3-bladed horizontal-axis wind turbine (HAWT) installed in the mid-throat for the optimum designs obtained by the metamodels. The results show that converging-diverging ducted openings can magnify the experienced wind speed by the turbine and enhance the available wind power. In addition, the use of different metamodels can lead to a variation of up to 153% in the estimated P available. For a small dataset, crude yet still acceptable accuracy can be achieved for Genetic Aggregation Response Surface and Kriging at a very low computational time. • Metamodels are used for the optimization of building-integrated ducted openings. • The performance of different commonly-used metamodels is systematically assessed. • Converging-diverging ducted openings can magnify the annual available wind power. • The use of different metamodels can significantly impact the predicted wind power. • Kriging and Genetic Aggregation Response Surface are recommended as models of choice. [ABSTRACT FROM AUTHOR]

The transport of dissolved contaminants in groundwater is usually described by the advection dispersion equation with reaction. Several numerical methods for solving the one-dimensional are available including finite difference methods, finite volume methods, and finite element methods. Stringent conditions, such as small Peclet (Pe) and Courant (Cr) numbers, must be satisfied to ensure the accuracy and stability of the numerical solutions. The practical finite analytic (PFA) method was applied to the solution of two solute transport problems: 1- One-dimensional advection-dispersion equation with reaction under advectiondominated conditions, and 2- One-dimensional pure advection equation with reaction. A triangular explicit PFA (EPFA) spatial-temporal computational molecule was developed. The EPFA solutions were compared with solutions from the quadratic upwind differencing (QUICK) scheme. For both cases, the EPFA solution gives accurate results as long as the Courant (Cr) was close to one. Stability analysis shows that the EPFA molecule is always stable for high Pe number. [ABSTRACT FROM AUTHOR]

Evaporative cooling by water spray is increasingly used as an efficient and environmentally-friendly approach to enhance thermal comfort in built environments. The complex two-phase flow in a water spray system is influenced by many factors such as continuous phase velocity, temperature and relative humidity patterns, droplet characteristics and continuous phase–droplet and droplet–droplet interactions. Computational Fluid Dynamics (CFD) can be a valuable tool for assessing the potential and performance of evaporative cooling by water spray systems in outdoor and indoor urban environments. This paper presents a systematic evaluation of the Lagrangian–Eulerian approach for evaporative cooling provided by the use of a water spray system with a hollow-cone nozzle configuration. The evaluation is based on grid-sensitivity analysis and validated using wind-tunnel measurements. This paper also presents a sensitivity analysis focused on the impact of the turbulence model for the continuous phase, the drag coefficient model, the number of particle streams for the discrete phase and the nozzle spray angle. The results show that CFD simulation of evaporation by the Lagrangian–Eulerian (3D steady RANS) approach, in spite of its limitations, can accurately predict the evaporation process, with local deviations from the wind-tunnel measurements within 10% for dry bulb temperature, 5% for wet bulb temperature and 7% for the specific enthalpy. The average deviations for all three variables are less than 3% in absolute values. The results of this paper are intended to support future CFD studies of evaporative cooling by water spray systems in outdoor and indoor urban environments. [ABSTRACT FROM AUTHOR]

Considering climate change and the rapid trend towards urbanization, the analysis of urban microclimate is gaining importance. The Urban Heat Island (UHI) effect and summer-time heat waves can significantly affect urban microclimate with negative consequences for human mortality and morbidity and building energy demand. So far, most studies on urban microclimate employed observational approaches with field measurements. However, in order to provide more information towards the design of climate adaptive urban areas, deterministic analyses are required. In this study, Computational Fluid Dynamics (CFD) simulations are performed to predict urban temperatures in the Bergpolder Zuid region in Rotterdam, which is planned to be renovated to increase its climate resilience. 3D unsteady Reynolds-averaged Navier–Stokes (URANS) simulations with the realizable k – ε turbulence model are performed on a high-resolution computational grid. The simulations include wind flow and heat transfer by conduction, convection and radiation. The resulting surface temperatures are validated using experimental data from high-resolution thermal infrared satellite imagery performed during the heat wave of July 2006. The results show that the CFD simulations are able to predict urban surface temperatures with an average deviation of 7.9% from the experimental data. It is concluded that CFD has the potential of accurately predicting urban microclimate. Results from CFD simulations can therefore be used to identify problem areas and to evaluate the effect of climate adaptation measures in these areas such as urban greening and evaporative cooling. [ABSTRACT FROM AUTHOR]

Abstract: High wind speed around high-rise buildings can lead to wind discomfort or wind danger at building balconies. This paper presents the evaluation of a new facade concept that is intended to significantly reduce the wind speed and therefore improve wind comfort on the balconies of high-rise buildings. The concept consists of a staggered semi-open second-skin facade in front of the balconies, which partly shields them from the wind. The concept is evaluated for the new 78 m high Park Tower in the urban area of Antwerp, where it will be implemented. 3D steady Reynolds-averaged Navier–Stokes Computational Fluid Dynamics (CFD) simulations are performed for the case with and without this facade concept. The simulations are made with the realizable k–ε turbulence model on a high-resolution grid. Validation is conducted using wind-tunnel measurements of surface pressure distribution on a building model with balconies. Wind comfort for the Park Tower is assessed with the Dutch wind nuisance standard NEN8100 for the case with and without the second-skin facade concept. The analysis shows that this concept is effective in providing a zone with pressure equalisation at the balconies. The related reduction in pressure gradients across the width of the facade strongly decreases the local wind speed. At many positions along the balconies this yields a wind comfort improvement of one or even two classes in the Dutch wind nuisance standard compared to the situation without implementation of this concept. [Copyright &y& Elsevier]

Abstract: Knowledge of the pressure distribution on building walls is important for the evaluation of wind loads and natural ventilation. Wind-induced pressure distributions are influenced by a wide range of factors including approach-flow conditions, urban surroundings and building geometry. Computational Fluid Dynamics (CFD) can be a valuable tool for determining mean wind pressure coefficients on building facades. However, while many CFD studies of mean wind pressure on buildings have been performed in the past, the vast majority of these studies focused on simple building geometries without facade details such as balconies. These details however can drastically influence the flow pattern and the overall pressure distribution on the facade. This paper presents a systematic evaluation of 3D steady Reynolds-Averaged Navier–Stokes (RANS) CFD for predicting mean wind pressure distributions on windward and leeward surfaces of a medium-rise building with and without balconies. The evaluation is based on a grid-sensitivity analysis and on validation with wind-tunnel measurements. It is shown that building balconies can lead to very strong changes in wind pressure distribution, because they introduce multiple areas of flow separation and recirculation across the facade. The results show that steady RANS, in spite of its limitations, can accurately reproduce the mean wind pressure distribution across the windward facade of the building. The average deviations from the wind-tunnel measurements are 12% and 10% for the building with and without balconies, respectively. In addition, also the important impact of the reference static pressure and the turbulence model are demonstrated. [Copyright &y& Elsevier]

We consider a system of nonlinear equations F(x) = 0. A new iterative method for solving this problem numerically is suggested. The analytical discussions of the method are provided to reveal its sixth order of convergence. A discussion on the efficiency index of the contribution with comparison to the other iterative methods is also given. Finally, numerical tests illustrate the theoretical aspects using the programming package Mathematica. [ABSTRACT FROM AUTHOR]

Experimental wind tunnel and smoke visualization testing was conducted to investigate the performance of a two-sided wind catcher. This type of wind catcher is divided internally into two halves for the purposes of air supply and extract. In this study, the two-sided wind catcher model was constructed of two similar one-sided wind catcher models, which were attached back to back. These one-sided models are 1 : 40 scale models of Kharmani's School wind catcher in the city of Yazd. Experimental investigations were carried out using an open-circuit wind tunnel, and both the induced volumetric airflow into the building and the pressure coefficients around all surfaces of the wind catcher model were measured at various wind angles. Additional experimental tests and computational fluid dynamics simulation of the wind catcher in the wind tunnel were also conducted in order to assess the accuracy of measurement procedures and the uncertainty of experimental results. To evaluate the stack effects on the natural ventilation performance of a two-sided wind catcher system, the results were compared to the corresponding results of a one-sided one. As a result of placing urban full-scale wind catchers in the boundary layer of atmospheric winds, the effect of this phenomenon was also examined experimentally. The experiments were performed when the wind catcher model with an adjoining house was placed in the wake of upstream objects, resembling neighbouring buildings. It was found that for an isolated two-sided wind catcher model, maximum efficiency is achieved at an air incident angle of 90°, and this can only be explained by the domination of a stack effect rather than dynamic pressure. At this air incident angle the wind catcher efficiency is ≈20 per cent more than the one at zero angle. The results show that the approaching air incident angles, the presence of an object upstream of the structure, and the blowing of atmospheric wind, influence phenomena such as pressure coefficients, induced airflow rate, and the airflow pattern of the two-sided wind catcher. The results show the potential of the two-sided wind catcher as a passive device for providing natural ventilation in buildings. [ABSTRACT FROM AUTHOR]

Abstract: Hydrodynamic performance of a one-sided wind catcher was investigated by experimental wind tunnel and smoke visualization testing. Wind catchers or what is called Baud-Geers in Persian language was a main component of buildings in central region of Iran and the neighboring countries. A Baud-Geer is a tower used to capture wind from external air stream and induce it into the building in order to provide natural ventilation and passive cooling. Due to geographical coordinates of the region, wind power and the direction of blowing wind, wind catchers are employed in different heights, cross sections of the air passages and the places and the number of the openings. The one-sided wind catcher has only one channel as a passage of induced air and is often related to the areas where there is prevailing wind. These Baud-Geers are employed to catch the wind blowing at higher elevations and direct it to the building, causing it to leave through windows, doors or other exhausted segments. In this study a 1:40 scale model of Kharmani''s School Baud-Geer was employed and the induced air flow rate into the test room and the pressure coefficients around all surfaces of its channel were measured for different values of approaching air incident angles. Using measured pressure coefficients, the theoretical values of ventilation air flow were estimated to evaluate ability of simplified models in natural ventilation studies. Due to placing of urban full-scale wind catchers in the boundary layer of atmospheric winds, the effect of this phenomenon was also examined. The experiments were conducted when the wind catcher model with adjoining house was placed in the wake of upstream objects, resembling neighboring buildings. It was found that for an isolated wind catcher model, the maximum efficiency is achieved at zero air incident angle. Also it was concluded that the angle of incidence of the wind, the presence of an upstream building around the structure and blowing of atmospheric wind influence the pressure coefficients, the rate and the direction of ventilation air flow. [Copyright &y& Elsevier]

The current work focuses on studying the hydrodynamic characteristics of flow in journal bearings lubricated with ferrofluid. The bearing has an infinite length and operates under incompressible laminar flow and steady conditions. Assuming linear behaviour for the magnetic material of the ferrofluid, the magnetic force was calculated. The displaced current-carrying infinitely long wire is used as a field model. This model gives a field distribution with a gradient in the circumferential and radial directions. The analysis is based on the numerical solution of the full Navier–Stokes equations using computational fluid dynamics techniques. Considering the complexity of the physical geometry, conformal mapping is used to generate an orthogonal grid and the governing equations are transformed in the computational domain. Discretized forms of the transformed equations are obtained by control volume method and solved by the SIMPLE algorithm. In the current study, cavitation effects are also considered by an appropriate cavitation model. To validate the computational results, a modified Reynolds equation has been obtained and solved by finite difference method. The results indicated that comparing with a conventional lubricant, the ferrofluid as a lubricant improves the hydrodynamic characteristics of journal bearings and provides a higher load capacity and a reduced friction coefficient. It will be evident that the other bearing characteristics depend on the applied field model. Numerical results of this analysis can be used to investigate the oil flow pattern and the hydrodynamic characteristics of journal bearings lubricated with ferrofluid. [ABSTRACT FROM AUTHOR]

Façade geometrical details can substantially influence the near-façade airflow patterns and pressures. This is especially the case for building balconies as their presence can lead to multiple separation and recirculation areas near the façades and hence large changes in surface pressure distribution. Computational fluid dynamics (CFD) has been widely used to investigate the impact of building balconies, mainly based on the steady Reynolds-averaged Navier-Stokes (RANS) approach. The objective of the present study is to evaluate the performance of steady RANS and large-eddy simulations (LES) in predicting the near-façade airflow patterns and mean surface pressure coefficients (C p) for a building with balconies for three wind directions θ = 0°, 90°, 180°, where 0° is perpendicular to the façade under study. The evaluation is based on validation with wind-tunnel measurements of C p. The results show that both RANS and LES can accurately predict C p on the windward façade for θ = 0° with average absolute deviations of 0.113 and 0.091 from the measured data, respectively. For the other two wind directions, LES is clearly superior. For θ = 90°, the average absolute deviations for RANS and LES are 0.302 and 0.096, while these are 0.161 and 0.038 for θ = 180°. Large differences are found in the computed flow fields on the balcony spaces. Because RANS systematically underestimates the absolute values of both C p and mean wind speed on the balconies, it is suggested that building design based on RANS might result in excessive ventilation and in too high wind nuisance level. Image 1 • Performance of RANS and LES is evaluated for a high-rise building with balconies. • RANS and LES accurately predict mean static pressure for wind direction 0°. • LES performs better than RANS for wind directions 90° and 180°. • Prediction of wind speed ratios on balcony spaces is systematically investigated. • Design based on RANS will result in too high wind nuisance level. [ABSTRACT FROM AUTHOR]

High-rise buildings can significantly increase the wind speed at pedestrian level, and knowledge of building aerodynamics and pedestrian-level wind (PLW) conditions is therefore imperative in their design. This study aims at evaluating different building geometry modifications to reduce PLW speed around an isolated high-rise building. Numerical simulations with computational fluid dynamics (CFD) are performed to evaluate the effect of canopies, podiums and permeable floors. To the best knowledge of the authors, a systematic study on the impact of these modifications on PLW conditions using validated CFD simulations has not been reported before. Grid-sensitivity analyses are performed and sub-configuration validation is applied using wind-tunnel measurements from the literature. It is shown that a canopy or a podium can significantly reduce the area-averaged PLW speed (up to 29%) and maximum PLW speed (up to 36%) around the high-rise building. In general, the PLW speeds decrease with increasing canopy or podium size. The introduction of a permeable floor to the building can reduce the maximum and area-averaged mean wind speed. However, when low-floor building layers are removed, adverse effects are noted, i.e. the average PLW speed increases (up to 21%) and the lower-speed wake region behind the building is reduced in size. Image 1 • A systematic parametric CFD study on reducing pedestrian-level wind speeds. • Canopies, podiums and permeable floors in various configurations are evaluated. • Mean wind speeds decrease with increasing canopy or podium size. • Permeable floors at mid-lower heights can decrease the maximum mean wind speeds. • Smaller podia and permeable floors at low heights can increase mean wind speeds. [ABSTRACT FROM AUTHOR]