Paper 7: Volume 5 No.1 June 2006 Edition
A Study on the Effects of Porosity on Discharge
Coefficient in Cross-Ventilated Buildings Based on Wind Tunnel Experiments
Takashi Kurabuchi1,
Yoshihiko Akamine2, Masaaki Ohba3,
Tomoyuki Endo1,
Tomonobu Goto3 and Motoyasu Kamata2
1Tokyo
University of Science
,
Japan
2University of
Tokyo
,
Japan
3Tokyo
Polytechnic University
,
Japan
Abstract
A study was performed on the effects of
porosity on discharge coefficient and airflow characteristics under the
condition where uniform approaching flow directly faces to and enters the
opening by using wind tunnel experiment and CFD analysis. The evaluation
was performed on porosities in the range 0.4% - 64%. The results of wind
tunnel experiments suggest that the discharge coefficient increases when
the porosity is higher. The results of CFD analysis reveal that the
contraction of airflow when it passes through the opening is correlated
with discharge coefficient, and that the discharge coefficient increases
when flow contraction does not occur. When porosity increases, the
retardment of the streamtube ceases to occur in the region upstream of the
opening, and this leads to the elimination of flow contraction, hence the
increase of discharge coefficient. When we evaluated the limitation of
application of the local dynamic similarity model on porosity, the
effectiveness of the model was confirmed well when the porosity was 16% or
lower regardless of wind direction. The validity of the model was also
confirmed under the condition where airflow goes along the wall surface
before reaching the opening even when the porosity was 36% or more.
Key words: Porosity,
discharge coefficient, wind tunnel experiment, CFD analysis, flow
contraction, local dynamic similarity model.
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