There is a component on the submarine that is easy to be ignored by many people. It is the propeller of the submarine. If we observe carefully, we will find that in most cases, the submarine propellers of all countries will not be displayed publicly, and what will be covered.

The dilemma of submarine propeller

The reason why the submarine propeller needs to be shielded is related to the stealth of the submarineThe basic principle of submarine propeller is to push the water forward by rotating the propeller. In this process, water will inevitably have a great flow rate, and the greater the flow rate of water, the lower the pressure, and the lower the liquid pressure, the lower the boiling point.

When the propeller rotates rapidly, the water driven by it will easily boil, resulting in a large number of bubbles. When these bubbles are generated and burst, they will produce noise, which will greatly affect the stealth of submarines. The enemy can locate the submarine by looking for these noises.

At this time, the designer of the submarine is in a dilemma. The speed of the submarine propeller is too fast to produce noise, but too slow speed will slow down the speed of the submarine. So how to drive more water flow when the speed of the submarine propeller is slower becomes the key to maintain the submarine speed and still ensure its invisibility.

Evolution of submarine propellers. Like the Russian nuclear submarine Belgorod, which directly adopts the design of parallel twin propellers, making it quite unique among a number of submarines. However, this design obviously requires the submarine to have a larger width and volume. If the submarine is directly widened and enlarged, it will cause a series of design problems.

So the current mainstream solution is to increase the blades of submarine propellers. With more propeller blades, more water will be carried at one time, so it is not necessary to turn too fast, so that the submarine can ensure enough concealment, and the speed is also fast.

In addition, the diameter of the propeller can not be large. If a large propeller and a small propeller turn the same number of times in the same time, the distance that the blade end of the large propeller will pass will be greater, which also means that the surrounding water flow speed will be faster. Therefore, if the diameter of the submarine propeller is too large, it will also increase the noise of the submarine.

In order to make the propeller drive more water in a limited diameter, the surface area of the blade must be large enough, so the blade of the submarine propeller will be designed with a large inclinationHowever, at this stage, designers from all countries are still not satisfied and still optimize the propeller. For example, some submarines will install hub and cap fins on the propeller.

Hubcap fin is simply to install a small propeller with proper angle on the propeller, which can carry water. When the submarine propeller rotates, the surface water flow will flow straight out along the hub and cap fins and disperse rapidly, which can reduce the flow velocity and thus achieve the purpose of reducing the submarine noise.

Another example is the pumping system. In simple terms, the propeller is covered with a shell, so that the flow of water is concentrated in the shell. The water out of the shell will not flow, or the flow speed is already very low. In this way, the water flow outside the propeller shell is difficult to generate bubbles, thus reducing the noise of the submarine.

In this way, the propeller seems to be a very common part, but the submarine propellers of the major military powers have undergone quite specific design. Once exposed, the diameter, shape and technical route of the submarine propeller can be known

Once you know these things, you can also know the best speed and the quietest speed of the propeller, so as to know a series of information such as engine type and output frequencyIf the information is known, the enemy will spend much less time in anti-submarine operations.

So at present, there are only two kinds of submarine propellers in the world, which will not be covered when they are displayed in public. One is the submarine used for foreign trade, which itself is to show the propellers to other countries. The other is the less advanced submarine. Does other countries know that its performance and technical characteristics are the same.

Noise reduction of submarines

In fact, in order to improve the stealth of submarines, countries have spent more than just on the propeller. For example, if we pay attention to the shape, we will find thatmodern attack nuclear submarines are basically streamlined, such as water droplets, which are large in front and small in backThis design can make the direction of the water flowing through the submarine surface more uniform, without eddy current and other conditions, thus reducing the noise.

For example, the strategic nuclear submarine will also be as streamlined as possible in its shape design. However, a large number of intercontinental missiles need to be installed on strategic nuclear submarines, which greatly occupies the space of submarines, making it difficult for strategic submarines to be streamlined in order to install intercontinental missiles.

However, when countries design strategic submarines, the pursuit of convectional lines is obvious to all. Like the turtle back of our strategic submarines, it is mainly due to the lack of experience in space layout design, and it is impossible to cram more things into the limited space. If our technology is sufficient, we will try our best to make strategic submarines like attack submarines in the shape of water droplets.

Even the design of submarine propellers has not come to an end, and countries are still optimizing their propellersFor example, China has also proposed the shaftless pumping route. In simple terms, it is to directly cancel the traditional shaft used for submarine propellers and drive the blades arranged inside the ring by the motor.

If shaftless pumping solves technical problems and is applied, it will directly make the mechanical noise of submarine propeller disappear, and make the water flow outside the propeller become similar to the situation that we mentioned above that”shaftless pumping” uses a cover to cover the propeller, and the water flow in the cover.

Therefore, the noise reduction of submarines is a very huge project, which requires a lot of technical intervention. In the eyes of many people, the common propeller is also high-tech and highly confidential. As countries further optimize the propeller in the future, the secrecy of the propeller will become stronger and stronger.