The influence of nozzle geometries and operating modes on the propulsive performance of continuous unsteady jet

In this paper, the effects of the nozzle geometry, formation time and duty cycle on the propulsive performance of continuous unsteady jets were experimentally investigated. Total of seven types of nozzles with different specific cavity shapes and nozzle lip angles were considered, which can be categorized into straight, contracting and expanding nozzles. The output thrust and input power of continuous unsteady jets in different modes of operation are obtained. Based on the experiment data, the power–thrust ratio was used to evaluate the energy conversion efficiency of continuous unsteady jets. The results indicate that the energy saving effect is positively correlated to the mean jet Reynolds number, which the continuous unsteady jet can have high efficiency in the operating mode with small formation time and duty cycle. Furthermore, it is proved that the small nozzle lip angle is conducive to the energy saving of unsteady jets. Analyzed from energy-optimal perspective, among the different nozzles, the hyperbolic nozzle has optimal propulsive performance under the formation time 3.03 and duty cycle 0.4. At this time, the power–thrust ratio is 0.018 watts per newton. The Vitosinski nozzle works under the formation time 2.82 has the widest duty cycle range for high efficiency operation.