Effects of roof overhangs on wind-driven rain wetting of a low-rise cubic building: A numerical study

Abstract Wind-Driven Rain (WDR) is known to be a major source of moisture loads on building envelopes and is responsible for numerous cases of building envelope failure. Roof overhangs are traditionally used and have been shown to be effective in reducing the exposure of buildings to WDR in certain climates. However, their effects on WDR wetting of facades are not fully understood nor quantified. In this work, CFD-based numerical simulations are employed to investigate the effects of overhangs of various sizes on the wind-driven rain wetting of a low-rise building under various wind and rain conditions. The numerical simulations are validated against experimental and numerical data in the literature. The results provide insights on the protecting mechanisms of overhangs. It has been shown that the introduction of an overhang can significantly change both the amount and the pattern of wind-driven rain wetting of the facade, especially in the upper region. The performance of the overhang is highly dependent upon its size, wind speed and wind angle, while the influence of rainfall intensity is small. A new global measure is introduced to quantify the effectiveness of overhangs in protecting facades from wind-driven rain. This index is shown to give a meaningful measure of the effects of the overhang.

[1]  T. V. Lawson,et al.  On the laboratory representation of rain impingement on buildings , 1972 .

[2]  Christopher J. Roy,et al.  VERIFICATION OF CODES AND SOLUTIONS IN COMPUTATIONAL SIMULATION , 2004 .

[3]  Yu-Ting Wu,et al.  WIND DRIVEN RAIN DISTRIBUTIONS AROUND STREET CANOPIES 1 , 2003 .

[4]  Hua Ge,et al.  Numerical Investigation of the Effects of Different Overhang Configurations on the Wind-Driven Rain Wetting of Building Facades , 2012 .

[5]  J. Carmeliet,et al.  Overview of three state-of-the-art wind-driven rain assessment models and comparison based on model theory , 2010 .

[6]  J. Carmeliet,et al.  A review of wind-driven rain research in building science , 2004 .

[7]  Theodore Stathopoulos,et al.  The numerical wind tunnel for industrial aerodynamics: Real or virtual in the new millennium? , 2002 .

[8]  R. Gunn,et al.  THE TERMINAL VELOCITY OF FALL FOR WATER DROPLETS IN STAGNANT AIR , 1949 .

[9]  Jan Carmeliet,et al.  Spatial and temporal distribution of driving rain on a low-rise building , 2002 .

[10]  Edmund C.C Choi,et al.  Simulation of wind-driven-rain around a building , 1993 .

[11]  R. Martinuzzi,et al.  Energy balance for turbulent flow around a surface mounted cube placed in a channel , 1996 .

[12]  Jan Carmeliet,et al.  On the validity of the cosine projection in wind-driven rain calculations on buildings , 2006 .

[13]  Jan Carmeliet,et al.  Intercomparison of wind-driven rain deposition models based on two case studies with full-scale measurements , 2011 .

[14]  Jan Carmeliet,et al.  Computational Fluid Dynamics simulations of wind-driven rain on a low-rise building : new validation efforts , 2005 .

[15]  J. Carmeliet,et al.  Validation of CFD simulations of wind-driven rain on a low-rise building facade , 2007 .

[16]  Jan Carmeliet,et al.  The mutual influence of two buildings on their wind-driven rain exposure and comments on the obstruction factor , 2009 .

[17]  A. Best,et al.  The size distribution of raindrops , 1950 .

[18]  Horia Hangan,et al.  Wind-driven rain studies. A C-FD-E approach , 1999 .

[19]  Shuzo Murakami,et al.  3-D numerical simulation of airflow around a cubic model by means of the k-ϵ model , 1988 .