Speaking of the shaftless propellers of ships, the most easy to think of are the shaftless pump-jet thrusters of submarines and the magnetic fluid propellers. However, these two types of propellers have inherent shortcomings at ultra-high speeds. For example, the shaftless pump-jet thrusters of submarines have moving parts. Then, at ultra-high speeds, the vibration and cavitation problems of the propellers will be very serious; Although the magnetic fluid thruster has no moving parts, it will heat the sea water, which is low in efficiency and cannot meet the high thrust requirements required for ultra-high speed. I believe everyone is familiar with the superiority of shaftless propellers. So for some ultra-high speed ships, such as high-speed bubble hovercraft with speeds of more than 80 knots, is there a shaftless propeller suitable for it? Today I will talk about a shaftless propeller suitable for ultra-high speed.
What propellers are used for ships with speeds exceeding 80 knots? The efficiency of the ram pump jet thruster is up to 60%
What propellers are used for ships with speeds exceeding 80 knots? The efficiency of the ram pump jet thruster is up to 60%
Propellers are a crucial part of the research of high-performance ships
With the development of super-high-speed surface effect ships, especially the development of high-speed bubble hovercraft, the propulsion of hovercraft becomes increasingly important. At present, high-speed bubble hovercraft mainly adopt two methods: supercavitation propeller and pump jet propulsion (water jet propulsion) driven by a water pump. Both methods can provide reasonable propulsion efficiency at high speeds. At the same time, when the speed of the ship does not exceed 80 knots (for the ship type, this speed is not fixed), the ratio of the weight of the propulsion device to the total weight of the ship It can also be controlled within a reasonable range. However, if you want to further increase the ship's speed, it will cause a sharp increase in the weight of the propulsion device, thereby limiting the ship's speed increase, so there is a critical value for high-speed propellers such as supercavitating propellers and pump-jet propellers.
What propellers are used for ships with speeds exceeding 80 knots? The efficiency of the ram pump jet thruster is up to 60%
What propellers are used for ships with speeds exceeding 80 knots? The efficiency of the ram pump jet thruster is up to 60%
Supercavitation paddle
According to the related formulas derived by G.F. Wislicenus (mainly applicable to hovercraft, the related formulas are not introduced here), it is known that the weight of the propulsion system that generates and transmits thrust is roughly proportional to the square of the speed. This shows that the weight of the machine related to speed is a critical factor. Therefore, if you want to further increase the speed of ships, you must find ways to reduce the weight of the propulsion device of high-speed ships and increase the ratio of the weight of the propulsion system to the total weight of the ship. Therefore, seeking new propulsion devices that are lighter in weight than existing propulsion systems has become the mainstream direction. The development of aviation technology provides a new way of thinking for ship propulsion devices. A new type of ship high-speed propulsion device born out of aviation propulsion device was born. It is a ram pump jet propulsion system with light weight and high speed.
What thruster does a ship with a speed exceeding 80 knots use? The efficiency of the ram pump jet thruster is up to 60%
What thruster does a ship with a speed exceeding 80 knots use? The efficiency of the ram pump jet thruster is up to 60%
Onboard gas turbines has played a big role in the development of high-speed ships
The composition of the ram pump jet thruster:
The underwater ram pump jet thruster (in order to distinguish it from the aviation ramjet engine), it is mainly composed of three parts: the ram water flow inlet, the mixing chamber and the two-phase nozzle.
What thruster does a ship with a speed exceeding 80 knots use? The efficiency of the ram pump jet thruster is up to 60%
What propellers are used for ships with speeds exceeding 80 knots? The efficiency of the ram pump jet thruster is up to 60%
The working principle of ram pump jet thruster
The working principle of the ram pump jet thruster:
During operation, the ram water flow inlet can increase the static pressure of the water flow entering the propulsion system. The method to increase the static pressure is to pre-diffuse the water inward or outward. After passing through the inlet, the water flow enters the mixing chamber, at which time compressed air is sprayed into the water flow. If the velocity of the fluid in the mixing chamber can reach a certain level, the turbulence itself can mix the water and the diffused bubbles, thereby reducing the average density of the working fluid. Connected to the mixing chamber is a two-phase nozzle. The bubbles generated in the mixing stage expand to the surrounding fluid in the two-phase nozzle and do work on the water phase, thereby accelerating the mixing speed. If the nozzle shape of the ram pump injection system is appropriate, the discharge velocity will be greater than the inlet velocity, resulting in forward thrust. This thrust is usually a combination of two forces, one is a positive boost acting on the front of the pipe, and the other is a negative boost acting on the inner and outer walls of the nozzle.
What propellers are used for ships with speeds exceeding 80 knots? The efficiency of the ram pump jet thruster is up to 60%
What thruster does a ship with a speed exceeding 80 knots use? The efficiency of the ram pump jet thruster is up to 60%
Punch pump jet propeller at zero speed
The ram pump jet propulsion system generally uses two types of air compression mixing processes, namely adiabatic mixing process (pressing hot air into the mixing chamber) and isothermal mixing process (compressed air temperature equal to the ambient temperature). Different types of air compression cycles have a very important impact on propulsion efficiency. For large-scale ram pump jet propulsion systems, an isothermal compression cycle should be used because it requires less installation shaft horsepower. However, this system must use multi-stage air compressors, and intercoolers must be installed between the multi-stage compressors. The air compressor can be directly connected with the host, so the whole device is particularly light. Because there is no rotating part in contact with water, the system is not prone to damage due to inhalation of debris.
What propellers are used for ships with speeds exceeding 80 knots? The efficiency of the ram pump jet thruster is up to 60%
What thruster does a ship with a speed exceeding 80 knots use? The efficiency of the ram pump jet thruster is up to 60%
The famous shaftless thruster "Inline Thruster" cannot avoid the problem of blade damage
In fact, the research on the principle of underwater ram pump jet propulsion is not very clear. However, it has a simple structure (composed of a pipe with a simple structure), has no moving parts in the underwater part, and has the characteristics of light weight; and it can form a two-phase jet by spraying compressed air into the high-pressure area of the pipe The expansion of the gas phase causes the fluid passing through the nozzle to gain acceleration to generate forward thrust. These characteristics are recognized by researchers. The ram pump jet propelling this two-phase fluid can be expressed by Euler and Bayleigh's equation of motion of bubbles relative to the water phase and the first law of thermodynamics. The thrust and propulsion efficiency can be calculated by using the computer to solve these equations. The general propulsion efficiency can reach 50%~60%, which is far higher than many traditional conventional propellers, so the ram pump spray device is a propulsion system very suitable for high-speed surface effect ships.
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