575 publications from this institution
This paper reports on past and ongoing wind-driven rain (WDR) research at the Laboratory of Building Physics, K.U.Leuven. It is based on the philosophy that WDR research consists of two main parts: (1) The assessment of the amount and intensity of WDR impinging on the building facade and (2) The assessment of the contact and surface phenomena that occur after impact of raindrops: splashing, evaporation, adhesion, absorption, runoff. The paper provides a brief overview of research in terms of full-scale measurements and CFD simulations of WDR on the VLIET test building and full-scale measurements with a newly developed test set-up for contact and surface phenomena.
High-rise buildings often give rise to wind discomfort problems. First, some brief general considerations on building aerodynamics and an illustration of wind nuisance are given. Next, the numerical study is presented that was performed to examine wind conditions in the designed Silvertop Tower passages. In a first step, the numerical model (CFD) will be validated by comparison with wind tunnel measurements for a simple slab type building. After that, it is applied to evaluate wind climate in the Silvertop Tower case study. Calculations will indicate that wind comfort in the passages is highly unacceptable. Various remedial measures are suggested and discussed, most of which conflict with the envisaged architectural design. Finally, a rather unconventional solution is suggested and analysed, where sliding doors are mounted at both ends of each passage. The opening and closing of the doors will be controlled based on local wind climate.
In a team time trial (TTT), the main strategy is based on drafting, where team members alternately take the lead while others ride behind the leading cyclist.TTTs can contain up to 9 riders of the same team.To the best of our knowledge, systematic aerodynamic studies of drafting groups from 2 up to 9 riders have not yet been published.Therefore, this paper presents such an analysis for up to 9 drafting cyclists in a single paceline, with wheel-towheel spacings d ¼ 0.05, 0.15, 0.5, 1 and 5 m.A total of 47 Computational Fluid Dynamics (CFD) simulations are performed with the 3D RANS equations, standard k-ε model and scalable wall functions and validated with wind-tunnel measurements.In groups of up to 5 identical riders with d up to 1 m, the last rider has the lowest drag but this is not the case for larger groups.A closely drafting group of 7, 8 or 9 riders has an average drag that is about half that of an isolated rider.However, for much longer theoretical single pacelines, a staggered peloton configuration can yet be about two times more drag efficient.
Natural ventilation is still a commonly applied way in building engineering to ensure a healthy and comfortable indoor climate. In this paper CFD simulations of the natural ventilation of a large semi-enclosed stadium in the Netherlands during the summer are described. Simulations are performed to assess the air exchange rate for a total of eight wind directions. The CFD model consists of both the complex stadium geometry and the urban environment in which the stadium is located. Validation of the CFD model is performed using full-scale 3D wind velocity measurements, furthermore, a grid sensitivity analysis is conducted. Comparison of the calculated air exchange rates showed that the wind direction has a significant effect on the air exchange rate; differences up to 100% were found for the air exchange rate, which can be explained by looking at the presence and size of the buildings that are situated upstream of the stadium.
An athlete's riding posture is a key element for aerodynamic drag in cycling. Tandem cycling has the complication of having two athletes in close proximity to each other on a single tandem bicycle. The complex flow-field between the pilot and stoker in tandem cycling presents new challenges for aerodynamic optimisation. Aerodynamic drag acting on two tandem road race setups and two track time-trial setups were analysed with computational fluid dynamics (CFD) simulations. For validation purposes, wind tunnel measurements were designed providing drag measurements from both tandem athletes simultaneously using a quarter-scale model. A max drag force deviation of 4.9% was found between the wind tunnel experiments and CFD simulations of the quarter-scale geometry. Full-scale CFD simulations of upright, crouched, time-trial and frame-clench tandem setups were performed. The drag force experienced by individual athletes in all investigated tandem setups was compared to that of solo riders to enhance understanding of the aerodynamic interaction between both tandem athletes. The most aerodynamic tandem setup was found to be the frame-clench setup which is unique to tandem cycling and had a CDA of 0.286 m2, and could provide an advantage of 8.1 s over a standard time-trial setup for a 10 km time-trial event.
In Computational Fluid Dynamics (CFD) simulations of the atmospheric boundary layer (ABL) the relation between inflow conditions and wall boundary conditions has been thoroughly investigated for Reynolds-averaged Navier-Stokes (RANS) modeling, whereas it yet needs to be evaluated for Large Eddy Simulations (LES). In the present paper streamwise homogeneity of flow profiles for LES of the neutral ABL over surfaces with different aerodynamic roughness lengths in combination with three different inflow turbulence generation methods is investigated. Specifically, one precursor and two synthetic methods have been considered along with three aerodynamic roughness lengths. The results show that the precursor method satisfactorily preserves the homogeneity of both mean velocity and turbulence kinetic energy, with respective average deviations up to 0.7% and 3.5% from target profiles at the outlet of the domain. Among the synthetic methods, less accurate but also less computationally demanding than the precursor method, the Vortex Method greatly outperforms the Spectral Synthesizer in terms of both mean velocity and turbulence kinetic energy. Lastly, terrain roughness is found to have only a weak influence on the performance of the inflow methods considered.
Climate change is expected to exacerbate urban microclimatic conditions and have adverse effects on human morbidity and mortality. However, there is limited knowledge on the impact of climate change on urban microclimate and human health for actual urban areas. In this study, we investigate the impact of climate change on urban microclimate and pedestrian thermal comfort within a complex district in Nicosia, Cyprus. Two climatic scenarios are considered: (i) current scenario based on meteorological conditions derived from field measurements performed in 2010, and (ii) future scenario for which meteorological conditions of 2050 are based on downscaled Regional Climate Models (RCMs). URANS CFD simulations are performed for the period of 9 to 10 July with a one-hour time-step. The results show that by 2050, the maximum air temperature at the pedestrian height of the case study area can increase by 2.3 °C which can increase heat-related mortality by more than 240%. In addition, the UTCI is expected to significantly increase especially in the afternoon hours with up to a 4.3 °C increase at 20:00. The "very strong heat stress" conditions (UTCI: 38-46 °C) are expected to prevail for a longer period during the day, increasing from 3.3 to 6.6 hours.
