Movement characteristics of fish in a jet fish pump

The jet fish pump (JFP), a special utilization of annular jet pump, is a potential tool for conveying fish in the aquatic industry because of its simple structure and lesser tendency toward mechanical injury. Based on high speed imaging, we studied the movement of grass carp in a JFP under different operating conditions including recirculation, normal flow and cavitation. Since the fish are prone to move against the main flow before being suctioned into the JFP, most of the fish transferred by the JFP display reverse body orientation. As the fish moves into the diffuser, an extrusion force combined with the circumferential and axial vortex makes the fish turn around or swirl. Moreover, cavitation, including the transient cavity cloud induced on the body of the fish and the stable cavity cloud in the throat and diffuser, results in a hostile environment for the fish and causes great injury to the body of the fish, which should be avoided in practical application. In this paper, we analyzed the possible damages to the body of the fish caused by these two types of cavity cloud. In addition, the influence of the fish themselves on the inner flow details is studied by monitoring the static wall pressure. An apparent pressure peak is captured at every monitored position caused by fish moving through JFP. The peak value corresponds to the moment that the fish blocks the flow in the throat because the resistance caused by the fish is at a maximum at that time. The results of this investigation provide a basis for the design of a JFP that can be used to minimize injuries to fish by optimizing the size of each component or regulating the operating conditions. (C) 2015 Elsevier Ltd. All rights reserved.