Intake rate through openings in the side wall of the duct

Abstract

© 2020 St-Petersburg State Polytechnical University. All rights reserved. Subject. In technological and general ventilation ducts with a given uniformity of intake is often needed to be designed. The calculation of pressure losses in such ducts is complicated by the lack of reliable information about the characteristics of the flows at the inlet to the intake openings and slots. Intensity of air intake through slot openings located on one and two opposite walls of the duct in a series of sequentially placed slots, which determines the presence of a transit air stream passing by the hole is calculated. The slots are perpendicular to the generatrix panel and can be opposite or offset relative to each other. The presence of a stagnant zone formed when the flow is cut off from a sharp edge at the inlet is taken into account. Methods. The search for a solution is carried out in the framework of ideal fluid jets theory using the Kirchhoff scheme and Chaplygin method of singularities, as well as by the numerical method using Flow3d software package, where the system of equations of plane turbulent motion was ended with "standard" k-e model. Results. The flow rates of the air entering through the slots were found, depending on their width and value of the transit flow. Dependencies for the attached flow with and without flow separation are obtained. The shape of the free streamline separating the jet and vortex zones, the compression coefficients of the jet are determined. Current flow lines are constructed for different values of the geometric parameters of the duct and the hole. Conclusion. Analytical and numerical calculations showed that the kinematics of currents and values of the attached flow rate are very similar, but the size and shape of the stagnant zone are significantly different. A numerical solution gives more physics of stagnant zone formation. It was found that flow separation reduces the associated flow rate. It was also found that the intensity of absorption is minimal with the opposite order of cracks.