Visualization of flow patterns induced by an impinging jet issuing from a circular planform

A four-jet impingement flow with application to high-performance VTOL aircraft is investigated. Flow visualization studies were conducted with water as the working medium. Photographs of different cross sections of the flow are presented to describe the properties of the fountain upwash and the stagnation-line patterns. The visualization technique involves the introduction of fluorescein-sodium, a fluorescent dye, into the jet flow and illumination by a sheet of light obtained by spreading a laser beam. Streak-line photographs were also taken using air bubbles as tracer particles. The strength and orientation of the fountain(s) were observed for different heights of the nozzle configuration above the ground and inclination angles of the forward nozzles.