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

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 P _R* 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 C_d from P_R* 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 C_d 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 (P_t). A simplified method was investigated for estimating the value of P_t 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 (P_r) and wind pressure (P_w) 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 P _t by the surface wind sensor very simply.