Investigation on the application of local dynamic similarity model to outflow openings

Variation of discharge coefficients with wind direction and opening position is one of the main factors decreasing accuracy of cross-ventilation flow rate prediction. The local dynamic similarity model was developed to solve this problem, and previous papers had validated it for inflow openings. In the present study, two experiments and a CFD analysis were carried out to investigate its validity for outflow openings. The study showed that discharge coefficient was not always determined uniquely by the dimensionless room pressure P _R*, and there were two types of relationship between discharge coefficient and P _R*. The difference of the relationship was attributed to the thickness of external airflow layer, which passed tangentially to the opening. Therefore discharge coefficient could be predicted from P _R* if either type of relationship was appropriately adopted according to the thickness of external airflow layer in each case. In addition, this study also showed the definition of dynamic pressure tangential to outflow openings, which is necessary to determine the P _R*. It can be concluded from the study that the local dynamic similarity model is valid for outflow openings as well as inflow openings.