Investigation of circular water film and normal impact force induced by an upward impinging jet on a horizontal plate

When a water jet impinges upward onto a horizontal plate vertically, it creates a circular water film geometrically analogous to a circular hydraulic jump. To explore the relationship between the circular water film and the hydrodynamic performance of the impinging jet, dimensional analysis was used to derive the relationships among the radius of the circular water film, impingement power, and jet impact force. The derived formulas were verified by laboratory experiments using high-speed imaging and force measurement on impinging water jets (nozzle diameters of 1.5-5.0 mm and volumetric flow rates of 0.9-7.2 l/min). The prediction model for the circular hydraulic jump radius proposed by previous researchers was revised with greater jet impingement power by considering the influence of the contact angle. Within a larger range of volumetric flow rates, a new wetting angle model considering the influence of nozzle diameter was proposed. Furthermore, an empirical model was proposed for predicting jet impact force coefficient from nozzle diameter and volumetric flow rate. It was revealed that the jet impact force coefficient also exhibits a weak dependence on the jet Froude number, in addition to the Reynolds number. The present research offers a new comprehensive framework for predicting circular water film and the jet hydrodynamic performance, which has significant implications for various applications of impinging jets.