Abstract
The cavitation in a vortex diode gives significant influences on a fluidic-pump performance. Its effect is more important in forward-flow state. Therefore it is a crucial aspect to clear the cavitation phenomena in the vortex diode in order to design the fluidic pump.
This paper describes the forward-flow cavitation of the vortex diode. A Zobel-type vortex diode was used as the test diode. According to a preliminary test, the cavitations were observed at both an axial nozzle and a tangential nozzle, and they affect each other. Therefore, experiments were performed in distinct three phases to make clear each cavitation. In phase-I and phase-II, we tried to examine the axial-nozzle cavitation and tangential-nozzle one respectively. And then, in phase-III, an overall test was performed to obtain their mutual interferences.
Through the three phases, states of the cavitations were observed carefully and the cavitation onset conditions were measured for individual cavitations. Then the cavitation onset patterns were analysed graphically and one design criterion for improvement was suggested.
The results obtained here are as follows:
1) The cavitation is generated in the axial nozzle at first, and follows in the tangential one. The cavitation onset leads to a choking state immediately.
2) The axial-nozzle cavitation shows an aspect of fixed cavitation. The tangential-nozzle cavitation consists of three types of cavitation such as travelling, fixed and vortex ones in compliance with down-stream pressure level. The onset cavitation-numbers of those cavitations show the tendencies to have the constant values individually in the experiments.
3) The pressure condition to avoid the cavitation occurrence has been given by a simple analysis.
4) It has been clarified that the value of the ratio of diameters of axial nozzle to tangential one should be 0.87 to improve the cavitation characteristics.
