Numerical predictions of the discharge coefficient of a window with moveable flap

Discharge coefficient and wind-pressure coefficient are the key input parameters for estimating the airflow rates in naturally ventilated building designs. This paper focuses on the study of the discharge coefficient (CD) in case of a moveable (bottom-hinged) window flap. Computational fluid dynamics (CFD) techniques are used for estimating the airflow through the window. Focus is given to the window on the windward side of the building. The first objective of this study is to validate the k-ε turbulent model for the estimation of airflow rates through the window. It is done by comparing the numerical results with existing results of full-scale measurements under a laboratory conditions. The second objective is to find an accurate method to estimate the airflow rate (using orifice plate equation) in the case of a window with a moveable flap. It is done by using CFD predictions together with the validated turbulent model. A single value of CD (usually 0.6 to 0.65) is not appropriate for the operable window with moveable flap. The results of the simulation validates that the k-ε turbulent model can predict the airflow rates within an acceptable range, when the pressure difference (across the opening) is higher than 0.5 Pa. This study also confirms that the single value of the CD is not sufficient for a window with moveable flap. At the end, a more accurate method is presented for estimating the airflow through a window with moveable flap.