Abstract
The operation of water-jet propulsion can generate nonuniform inflow that may be detrimental to the performance of the water-jets. To reduce disadvantages of the nonuniform inflow, a rim-driven water-jet propulsion was designed depending on the technology of passive magnetic levitation. Insufficient understanding of large performance deviations between the normal water-jets (shaft) and permanent maglev water-jets (shaftless) is a major problem in this paper. CFD was directly adopted in the feasibility and superiority of permanent maglev water-jets. Comparison and discussion of the hydraulic performance were carried out. The shaftless duct firstly has a drop in hydraulic losses ( K1), since it effectively avoids the formation and evolution of the instability secondary vortex by the normalized helicity analysis. Then, the shaftless intake duct improves the inflow field of the water-jet pump, with consequencing the drop in the backflow and blocking on the blade shroud. So that the shaftless water-jet pump delivers higher flow rate and head to the propulsion than the shaft. Eventually, not only can the shaftless model increase the thrust and efficiency, but it has the ability to extend the working range and broaden the high efficiency region as well.
Highlights
In many vessels, water-jets are required to achieve speeds of 30+ knots where conventional propeller solutions are unable to overcome the associated issues of cavitation, which in turn can lead to thrust breakdown and material failure
In order to investigate the feasibility and superiority of the shaftless water-jet propulsion, this paper eliminated the upstream driving shaft and used a passive magnetic pump by rim driven for water-jet system, where the rotor, stator, and intake duct are the major flow components
This paper presents the prototype and model of permanent maglev pump for water-jet propulsion, demonstrates the stable levitation of the water-jet rotor, and discusses the hydraulic performance by theoretical analysis and numerical analysis
Summary
Water-jets are required to achieve speeds of 30+ knots where conventional propeller solutions are unable to overcome the associated issues of cavitation, which in turn can lead to thrust breakdown and material failure. In order to investigate the feasibility and superiority of the shaftless water-jet propulsion, this paper eliminated the upstream driving shaft and used a passive magnetic pump by rim driven for water-jet system, where the rotor, stator, and intake duct are the major flow components. Earnshaw’s theorem is not applied in dynamic equilibrium of permanent maglev There should be another theory to answer the question about whether a rotating passive magnetic levitator can achieve a stable equilibrium. A patented novel passive magnetic bearing [15] was applied in rotary pump and turbine machine; Figure 2 shows that the rotors of these devices could be levitated in a stable manner if the rotating speed is high enough. This paper presents the prototype and model of permanent maglev pump for water-jet propulsion, demonstrates the stable levitation of the water-jet rotor, and discusses the hydraulic performance by theoretical analysis and numerical analysis
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