The pump jet thruster of a ship is commonly referred to as a water jet thruster, but due to the widespread use of shaftless pump propulsion in submarines in China, many people believe that the pump jet thruster is the thruster of submarines. In fact, the pump jet thrusters used on submarines are generally "externally suspended axial flow pump jet thrusters", which belong to a type of jet thrusters and can be suitable for various types of ships (including submarines). Since the pump jet propulsion system of submarines is so well-known, I will briefly explain it today, and then focus on the difference between its front and rear guide wheels.
Nuclear submarines using pump jet propulsion
The structure and principle of pump jet thrusters
The externally suspended axial flow pump water jet thruster (pump water jet thruster) mainly consists of three parts: rotor (impeller), stator (guide wheel), and annular guide pipe. The rotor and stator are both wing shaped circular cross-section blades, with one rotating to perform work and the other fixed to guide flow, both of which are covered by conduits. During operation, the motor (turbine) drives the impeller to do work on the fluid, causing it to spray out at high speed and generate thrust through the reaction force of water.
Internal structure of external suspended axial flow pump water jet thruster
The main advantage of pump jet thrusters lies in the segmentation effect of the duct on the flow field, which enables the impeller of the propulsion pump to work in a uniform flow field and reduces the expansion of the working fluid. If specific conduits and guide wheels are added, the pump jet thruster will have good anti cavitation performance in the high-speed range. Therefore, it improves the noise level and efficiency of submarine thrusters at high cruising speeds. According to statistics, when the speed is above 20 knots, pump jet thrusters have significant advantages. It is precisely because of such advantages that more and more high-speed submarines, especially attack type nuclear submarines, are adopting pump jet thrusters.