Experimental and numerical investigations into flow features in an intake duct for the waterjet propulsion under mooring conditions

The waterjet propulsion is widely applied in the marine vessels over 30 knots,and the intake duct is considered as an essential component that strongly relates to the propulsion performance.This paper sheds light on the flow features inside an intake duct under mooring conditions by using the particle image velocimetry(PIV)technique with three-dimensional(3D)numerical simulations.The hydraulic loss gradually increase as the flow-rate increases.According to analyses via the Bernoulli equation,the hydraulic loss is composed of the frictional head loss(h_(f)~V^(1.75))and the local head loss(h_(j)~V^(2.0)).A recirculation region is observed near the duct lower wall with a high-velocity flow near the upper wall,and subsequently a shear flow presents in the horizontal straight pipe with an obvious velocity gradient.Three-dimensional simulations demonstrate that the vortex pair is very strong in the recirculation region and then it gradually decreases as the fluid flows downstream.With the flow-rate increasing,the non-uniformity at the duct outlet firstly increases to a peak and then slightly decreases,while the perpendicularity at the duct outlet dramatically decreases to a minimum and then increases.This work not only reveals some physics of the waterjet propulsion under mooring conditions,but also promotes its efficient operation.

Nozzle Optimization for Water Jet Propulsion with A Positive Displacement Pump

In the water jet propulsion system with a positive displacement （PD） pump, the nozzle, which converts pressure energy into kinetic energy, is one of the key parts exerting great influence on the reactive thrust and the efficiency of the system due to its high working pressure and easily occurring cavitation characteristics. Based on the previous studies of the energy loss and the pressure distribution of different nozzles, a model of water jet reactive thrust, which fully takes the energy loss and the nozzle parameters into consideration, is developed to optimize the nozzle design. Experiments and simulations are carried out to investigate the reactive thrust and the conversion efficiency of cylindrical nozzles, conical nozzles and optimized nozzles. The results show that the optimized nozzles have the largest reactive thrust and the highest energy conversion efficiency under the same inlet conditions. The related methods and conclusions are extended to the study of other applications of the water jet, such as water jet cutting, water mist fire suppression, water injection molding.

Research on Flow Loss of Inlet Duct of Marine Waterjets

In the process of performance prediction of waterjet system,the flow loss of inlet duct is usually reckoned by the rule of thumb. But its value is often overestimated to some extent,resulting in error of prediction accuracy. This paper introduces a new method to determine the flow loss by means of computational fluid dynamic (CFD). Firstly,the fluid field around waterjet system is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations using commercial CFD code Fluent. Then an additional User-Defined Scalar (UDS) equation is embedded into Fluent to get the virtual dividing surface between the internal flow ingested into the inlet duct and the external flow beneath the hull,which is named as streamtube. By virtual of the streamtube the flow loss can be calculated according to the difference of total pressure between the duct outlet and the capture area ahead of the intake. The results from CFD calculation show that the flow loss coeflcient of a typical flush-type inlet duct is varying from 0.05 to 0.12 at different operation conditions,being obviously less than the value of 0.2-0.3 from empirical rules. With the results of this paper the prediction accuracy on propulsive performance of the waterjet system can be improved further.