1,771 research outputs found
New initiative : "ten questions" paper series in building and environment
No full text1. Brief description of the initiative Building & Environment is launching a new initiative for a series of "Ten Questions" papers, to be published in a pre-described format. "Ten Questions" papers should deal with a well-defined topic and should be centered around a selection of ten relevant and topical questions. Submissions are based on invitation only by the Editor of the Special Initiative (SI), Prof. Bert Blocken. Papers will be recruited in a way that ensures balanced coverage of all topics in the scope of Building and Environment. The papers should be (co-)authored by established researchers in the field with proven expertise on the topic, typically by an extensive track record of previously published books and/or peer-reviewed journal papers. The questions are selected and answered by the author(s). The questions should be such that the paper is visionary, authoritative and can provide younger researchers directions for future research
Intercomparison of wind-driven rain models based on a case study with full-scale measurements
Full text linkThree different calculation models for wind-driven rain (WDR) are compared: the
semi-empirical model in the ISO standard for WDR (ISO), the semi-empirical model by Straube and Burnett (SB) and the CFD model by Choi, extended by Blocken and Carmeliet. This paper builds further on the comparison of these models for idealized building configurations and fixed wind and rain conditions in [Blocken et al., 2010. Comparison of calculation models for winddriven rain deposition on building facades, Atmospheric Environment 44(14): 1714-1725]. In the present paper, these models are applied to a high-rise monumental tower building, for a transient rain event, and the model results are compared with full-scale measurements. The agreement between the CFD results and the measurements is quite good at the upper part of the facade, while the ISO and SB model show large discrepancies at these facade positions
Energy saving potential of night ventilation: Sensitivity to pressure coefficients for different European climates
Full text linkThe suitability of night ventilation to reduce the cooling demand in buildings can be evaluated by
coupling Airflow Network Models to Building Energy Simulation tools. To estimate wind-induced
ventilation, pressure coefficients (Cp) on the building envelope are key inputs, as well as local wind speed
and direction. Cp data obtained by primary sources such as measurements or CFD simulations are
considered the most reliable but can be difficult to obtain. An easy alternative are Cp secondary sources,
such as databases providing literature data correlations. Therefore an issue arises regarding the choice of
the source of pressure coefficients.
This paper investigates the effects of Cp from primary and secondary sources on the predicted energy
saving potential of night ventilation of an isolated office building for several European climates and some
relevant design conditions and simulation parameters. Different Cp sources produce a dispersion of Cp
data and differences in the calculated night ventilation rates up to 15%. Contrary to what might be
expected, these differences influence only marginally the resulting passive cooling effects. Overall a
stronger impact is observed for the colder climates, where higher temperature differences occur between
desired indoor temperature and night-averaged outdoor temperature. Finally, for the building under
study, the choice of the Cp source appears less crucial than the choice of other building simulation
parameters, such as the internal Convective Heat Transfer Coefficient. This study can support building
designers towards accurate energy simulations of naturally ventilated buildings
Vortex dynamics and radial outflow velocity evolution in downburst-like winds
Full text linkDownbursts can cause severe winds near ground level, potentially damaging buildings and structures. A particular problem is that downburst-induced wind action is not considered in the design stage as it is not included in the building codes. This paper provides an in-depth characterization of a downburst flow field including its vortical structures in both space and time. The analysis is based on Large Eddy Simulations (LES) to reproduce dedicated experiments of a vertical downburst carried out in the test chamber of the WindEEE Dome laboratory. The trajectory of the radial velocity maxima is evaluated, which indicates that the height of the maximum velocity increases with the traveled distance after having produced the strongest wind gusts. The spatial evolution of the convective velocity of the primary vortex across the test chamber is evaluated and three regions are distinguished: the speed-up (up to r/D = 1.25), the slow-down (1.25 < r/D < 2.29) and the deflection region (r/D > 2.29). The analysis indicates that trailing ring vortices produce higher outflow velocities than the primary vortex after a sufficient time span, causing the radial locations between 0.8 and 1.8 r/D to be continuously exposed to strong gusts
Scientification of design and internationalisation of research
No full textThe role of research in the Department of Architecture, Building and Planning is shifting. Design must become more scientific and research more international - and above all, interdisciplinary. In search of greater perspective on this new interpretation of research, this article presents the views of the Department’s Pieter van Wesemael and Bert Blocken.
Designing, developing, researching - on change, trends, innovation, tradition and the scientification of design
Large-scale forcing effects on wind flows in the urban canopy: impact of inflow conditions
Full text linkWind flow modeling in urban areas is usually performed by means of Wind-Tunnel (WT) testing or Computational Fluid Dynamics (CFD) simulations. Results obtained with both techniques can be affected by the boundary conditions. This study aims at investigating how two sets of inflow conditions, termed set 1 and set 2 and calculated respectively using the equations proposed by Richards and Hoxey (1993) and Tominaga et al. (2008), may affect the accuracy of the results in terms of mean wind speed, turbulent kinetic energy, yaw and pitch angles when predicting wind flows in urban areas. 3D steady RANS simulations were performed for a selected urban area (“Quartiere La Venezia” in Livorno, Italy). WT tests on the same urban model were used to validate the CFD simulations. Mean wind profiles at 25 positions in the urban area were compared and the statistical performance was quantified using four metrics for both sets of inflow conditions. The results obtained using the two sets of inflow conditions showed comparable performances in terms of wind flow predictions in the urban canopy, which means that at the building scale there is no need to use more accurate conditions because they are as effective as the simpler ones
Comparison between the Impinging Jet Model and Experimental Stationary Downbursts
No full textThe phenomenon of downdraft from thunderstorm cloud which after the touch-down spreads radially is well-known in both the meteorological and the wind-engineering community and has been under active investigation by a lot of authors since more than 50 years. In this paper, a simple impinging jet simulation has been compared with experimental downbursts in order to understand to which extent this approach can be considered realistic for practical applications.
Wind tunnel experiments have been carried out at the University of Western Ontario’s WindEEE Dome Research Institute. The radial velocity was measured at various locations and the obtained profiles have been used as a reference for the comparison with the impinging jet, simulated by a steady-state Computational Fluid Dynamics (CFD) approach. As downbursts are highly transient phenomena, the impinging jet solution has been compared with the measured velocity profiles, which typically show three parts, i.e. ramp-up, plateau and dissipation, aiming to identify which part (if any) of the downburst lifecycle can be adequatelly represented by the steady-state numerical simulation
Ten iterative steps for model development and evaluation applied to Computational Fluid Dynamics for Environmental Fluid Mechanics
No full textComputational Fluid Dynamics (CFD) is increasingly used to study a wide variety of complex Environmental Fluid Mechanics (EFM) processes, such as water flow and turbulent mixing of contaminants in rivers and estuaries and wind flow and air pollution dispersion in urban areas. However, the accuracy and reliability of CFD modeling and the correct use of CFD results can easily be compromised. In 2006, Jakeman et al. set out ten iterative steps of good disciplined model practice to develop purposeful, credible models from data and a priori knowledge, in consort with end-users, with every stage open to critical review and revision (Jakeman et al., 2006). This paper discusses the application of the ten-steps approach to CFD for EFM in three parts. In the first part, the existing best practice guidelines for CFD applications in this area are reviewed and positioned in the ten-steps framework. The second and third part present a retrospective analysis of two case studies in the light of the ten-steps approach: (1) contaminant dispersion due to transverse turbulent mixing in a shallow water flow and (2) coupled urban wind flow and indoor natural ventilation of the Amsterdam ArenA football stadium. It is shown that the existing best practice guidelines for CFD mainly focus on the last steps in the ten-steps framework. The reasons for this focus are outlined and the value of the additional - preceding - steps is discussed. The retrospective analysis of the case studies indicates that the ten-steps approach is very well applicable to CFD for EFM and that it provides a comprehensive framework that encompasses
and extends the existing best practice guidelines
Characterization of experimentally produced isolated downburst winds by Large Eddy Simulations
No full textCFD simulation of cross-ventilation for a generic isolated building: Impact of computational parameters
No full textAccurate CFD simulation of coupled outdoor wind flow and indoor air flow is essential for the design and evaluation of natural cross-ventilation strategies for buildings. It is widely recognized that CFD simulations can be very sensitive to the large number of computational parameters that have to be set by the user. Therefore, detailed and generic sensitivity analyses of the impact of these parameters on the simulation results are important to provide guidance for the execution and evaluation of future CFD studies. A detailed review of the literature indicates that there is a lack of extensive generic sensitivity studies for CFD simulation of natural cross-ventilation. In order to provide such a study, this paper presents a series of coupled 3D steady RANS simulations for a generic isolated building. The CFD simulations are validated based on detailed wind tunnel experiments with Particle Image Velocimetry. The impact of a wide range of computational parameters is investigated, including the size of the computational domain, the resolution of the computational grid, the inlet turbulent kinetic energy profile of the atmospheric boundary layer, the turbulence model, the order of the discretization schemes and the iterative convergence criteria. Specific attention is given to the problem of oscillatory convergence that was observed during some of these coupled CFD simulations. Based on this analysis, the paper identifies the most important parameters. The intention is to contribute to improved accuracy, reliability and evaluation of coupled CFD simulations for cross-ventilation assessment
- …
