Coarse-graining characterization of the room flow circulations due to a fan-array wind generator

Abstract

Fan-array wind generators (FAWGs) are being employed for unmanned aerial vehicle testing. Such testing requires uniform blowing generated from the FAWGs. However, achieving uniform blowing is impeded by the wall effects within the enclosed room. These wall effects also lead to complex flow circulations. Understanding the room flow circulations can provide insight into restoring the uniformity of FAWG blowing. In this study, a coarse-graining characterization methodology is proposed to extract the room flow circulations. The key enabler is discretizing the flow domain into regular boxes as coarse-grained units and reducing the continuous flow field to flow transfers among the units. The flow circulation structure is characterized by kinematic features, i.e., the flow loop paths. The methodology is demonstrated on a numerical simulation of the room flow generated by the world's largest FAWG in the Shenzhen unmanned aerial vehicle test center. First, an analysis of the room flow kinematics shows a deflection and velocity decay of the jet-like flow. Second, two- and three-dimensional kinematic feature identifications indicate that horizontal circulations dominate the room flow. Third, two triangular prisms are introduced to manipulate the whole room circulations to improve the flow characteristics in the drone testing region. The right-angle prism reduces the flow deflection and enhances the flow activity in the test region by orienting flow circulations from horizontal to vertical. Meanwhile, the acute-angle prism creates complex flow circulations. The proposed methodology facilitates the identification and improvement of kinematic features and contributes to the physical understanding of a flow circulation structure in complex configurations.