Abstracts
Paper 9: Volume 4 No.3 December 2005 Edition
Local Dynamic Similarity
Concept as Applied to Evaluation of Discharge Coefficients of
Cross-Ventilated Buildings - Part 1 Basic
Idea and Underlying Wind Tunnel Tests; Part
2 Applicability of Local
Dynamic Similarity Concept; Part 3
Simplified Method for Estimating Dynamic Pressure Tangential to
Openings of Cross-Ventilated Buildings
Takashi
Kurabuchi1, Masaaki Ohba2, Tomonobu Goto2,
Yoshihiko Akamine3,
Tomoyuki
Endo1 and Motoyasu Kamata3
1Tokyo
University of Science
,
Japan
2Tokyo
Polytechnic University
,
Japan
3University of
Tokyo
,
Japan
Abstract
A model has been proposed for evaluating the discharge coefficient
according to the flow angle at an inflow opening for cross-ventilation.
This model is based on the fact that the cross-ventilation flow structure
in the vicinity of an inflow opening creates dynamic similarity under the
condition that the ratio of cross-ventilation driving pressure to dynamic
pressure of cross flow at the opening is consistent. It was confirmed from
a wind tunnel experiment that the proposed model can be applied almost
regardless of wind direction and opening position. Change of pressure
along the stream tube of a cross-ventilated flow was estimated from the
results of Large Eddy Simulation, and was set as the basis of model
preparation.
In order to perform detailed evaluation on the
applicability of the local dynamic similarity concept, wind tunnel
experiments were conducted under conditions where the opening positions
and the arrangement of buildings were changed. As a result, it was found
that the discharge coefficient Cd can be predicted accurately
from PR* for most of the opening positions, even if the
approaching flow angle is varied or another building is standing near the
opening. It was also found that there are no substantial problems for
predicting Cd from PR* when the direction of
interfering cross flow is changed or there is wall/floor near the opening
disturbing the diffusion of incoming airflow. However, it should be noted
that the prediction accuracy of Cd is lowered when these
conditions occur simultaneously.
To predict the ventilation flow rate based on the local dynamic similarity
model, it is necessary to estimate the value of dynamic pressure
tangential to openings (Pt). A simplified method was
investigated for estimating the value of Pt by Irwin’s
surface wind sensor. The wind velocity tangential to the wall measured by
this sensor was broadly consistent with the value measured by a hot-wire
anemometer. Moreover, Pt calculated from the wind
velocity measured by the surface wind sensor was compared with the
differential pressure between total pressure (PT) and
wind pressure (PW) measured directly at the opening.
They were broadly consistent with each other. From these results, it is
concluded that we can estimate the value of Pt by the
surface wind sensor very simply.
Key words: Local
dynamic similarity model,
ventilation flow rate, inflow opening, total pressure, wind tunnel
experiment, CFD, LES, cross-ventilation,
discharge coefficient, inflow angle, dynamic pressure.
Kiyota N and Sekine T: (1989) “Experiment
study on pressure loss at the opening of wall surface (Part2)”, J.
Archt. Plann. Environ.
Eng.
, AIJ, 398: pp47-57.
Kurabuchi T, Ohba M, Arashiguchi A and Iwabuchi T: (2000)
“Numerical study of airflow structure of a cross-ventilated model
building”, The 7th International Conference on Air
Distribution in Rooms ‘ROOMVENT 2000’, pp313-318.
Kurabuchi, T. Ohba, M. Endo, T. Akamine, Y. and Nakayama, F: (2004)
“Local Dynamic Similarity Model of Cross-Ventilation Part1-Theoretical
Framework”, The International Journal of Ventilation, 2,
(4), pp371-382.
Ohba
M, Kurabuchi T, Endo T, Akamine Y, Kamata M and Kurahashi A: (2004)
“Local dynamic similarity of cross-ventilation, Part 2 Application of
local dynamic similarity model”, The
International Journal of Ventilation, 2, (4), pp383-393.
Sawachi T, Narita K, Kiyota N, Seto H, Nishizawa S and Ishikawa Y:
(2004) “Wind Pressure and Air Flow in a Full-Scale Building Model under
Cross Ventilation”, The International Journal of Ventilation, 2,
(4), pp343-358.
Vickery BJ and Karakatsanis: (1987) “External wind pressure
distribution and induced internal ventilation flow in low-rise industrial
and domestic structures”, ASHRAE Transactions, 93, Part2,
pp2198-2213.
Wu H. and Stathopoulos T:
(1994) “Further Experiment on Irwin’s Surface Wind Sensor”, Journal
of Wind Engineering and Industrial Aerodynamics, 53, pp441-452.
|
IJV Volume 4 No 3
Contents
Paper
1: Vent Configuration
Paper
2: Passive Cooling
Paper
3: Post Occupancy
Paper
4: Hybrid Ventilation
Paper
5: Bioclimate
Paper
6: Human Factors
Paper
7: CFD Reliability
Paper
8: Wind Pressure
Paper 9: Similarity
Concept
|
