"Jimmy, Bob, you know a lot about the structure of car engines, so let me ask you a little question about aircraft engines, of course, this is not a test for the two of you, just answer if you know, forget if you don't know!"

Claire walked up to the huge engine and pointed to something like the fan.

"Do you know what this is?"

Bob looked at it and didn't say anything, of course he knew that this thing was a fan, the thrust of the plane was generated by the fan, the first generation of jet planes had such parts on it, but that kind of is called a propeller engine, obviously the fan in front of him is more precise, the blades are dense and smooth like a knife, today's power systems are all internal combustion type, the output power is much larger, the thrust generated by the strong air flow on the blades can blow the car out, ordinary materials simply can't withstand such power, at least in the material I don't know how much。

"It's supposed to be an airplane fan, but it's a turbofan instead of a regular fan! ”

Liu Lang replied that he was not an immortal, he did not have the ability to predict the future, he had very little contact with the relevant materials about aircraft engines, and he had only seen some rough information in the library, but he had not learned it, and Liu Lang also knew nothing.

"I don't know, okay, then I'll teach you two a lesson!

This is indeed called a turbofan, which was developed from a turboprop jet engine, which is characterized by the large area of the first stage compressor and is also used as an air propeller to push some of the intake air through the periphery of the jet engine. The part through which the air in the core part of the engine passes is called the internal duct, and the outer part of the core through which only the fan air passes is called the outer duct.

The turboprop engine has too low exhaust speed and limited thrust, so it is necessary to improve the efficiency of the jet engine. The efficiency of the engine includes two parts: thermal efficiency and propulsion efficiency, and the thermal efficiency can be improved by increasing the temperature of the gas before the turbine and the boost ratio of the high-pressure compressor. This is because high-temperature, high-density gases contain more energy. ”

Claire was very happy, because it was rare to hear Liu Lang say that he wouldn't.

"That's how turbo engines work! These turbofans must be very different from the previous propeller fans!"

Liu Lang asked again.

"Of course, the air coming out of the turbine can blow a house down, hit ordinary steel, and it will have to be shattered in less than half a year......... Okay, I'm going to tell you about the structure of this turbofan today!"

Claire was in a mood and began to speak.

"The turbine blade is mainly composed of four parts: the crown of the blade, the blade body, the edge plate and the blade root.

This is the crown of the blade, and in order to improve the turbine efficiency, a crown structure similar to the edge plate is often used at the upper end of the blade. Its function is to reduce the air leakage of the blade tip from the blade basin to the back of the blade, reduce the secondary loss, and improve the turbine efficiency; the friction between the crowns of adjacent blades can absorb the vibration energy and play a role in vibration reduction; the crowns of the rotor blades of the same stage are pressed against each other, which can enhance the rigidity of the blade and improve its vibration resistance; and the crowned blades can adopt the thin blade type that is more favorable to aerodynamics. At present, the commonly used crown shapes are mainly parallelogram and zigzag crowns.

The blade body, its function is mainly to realize the aerodynamic characteristics of the blade, the cross-sectional shape of the blade body of different heights is selected by the aerodynamic design, and the airflow channel is formed between the blade bodies of the adjacent blades in the circumference, which is used for high-temperature and high-pressure gas to flow through and expand to do work;

The function of the edge plate is mainly to form an independent airflow channel to ensure that high-temperature gas will not flow into the turbine disk, seal, support and other components with poor temperature resistance outside the airflow channel. The edge plate is between the blade body and the blade root, and generally adopts a square structure, and the upper and lower parts are connected with the blade body and the blade root through the transition section respectively, and the blade edge plate of the same rotor forms a closed annular structure.

The function of the blade root is mainly to connect the blade and the wheel disc in order to transmit power to the rotor shaft connected with the wheel disk. At the lower end of the blade root, the part connected to the turbine disc generally adopts a fir tree-shaped tenon, and its advantages are: the circumferential size of the tenon is small, more blades can be installed on the wheel rim, and the output power is large; a plurality of tooth surface force transmission, strong bearing capacity, large safety margin; large contact area, which is conducive to heat dissipation and friction and vibration reduction; gap fitting, can expand freely after heating, can reduce thermal stress, and is convenient to disassemble and assemble. ”

The two listened very carefully, and Bob took out a piece of paper from his bag and wrote it down, which is Professor Claire's private goods, and not everyone can learn it.

Of course, Liu Lang doesn't use pen and paper, his brain is equivalent to a computer, Bob remembers it very carefully, but he thinks it's nothing, Professor Claire just introduced the composition, which is equivalent to the explanation of nouns, and it is not of great use to the substance.

"I think this kind of blade is very special, the structure is different, and this material is also very tough, such a thin blade is easy to twist when it rotates at extreme speed, Professor, how are the blades of this engine made?"

Liu Lang asked pretending to touch the sharp blade.

"You asked very professionally, this kind of blade is a typical free-form surface parts, this kind of parts have a characteristic, that is, to be thin, but there will be a result, that is, it is easy to deform during processing, so it is very strict in the material, generally speaking, the material is stainless steel, but this is not ordinary stainless steel, Monel alloy, INCONEL, titanium and nickel-based difficult-to-machine alloy materials!"

Claire replied.

"Oh, Monel, the alloy material of titanium and nickel!"

Liu Lang wrote it down.

"Professor, you said that these alloys are very hard materials and are difficult to machine, but this kind of blade is extremely precise, which will put forward higher requirements for the machining process and the tools used for machining, do you know this?"

Liu Lang asked again.

"Haha, Jimmy, this kind of problem can't bother me, okay, then I'll give you a brief explanation of this problem.

In the processing of blades, there are three difficulties in blade processing: milling process circumference, blade root processing, milling ribbed holes......... These blades are hollow, and this casting method is very difficult.

Hollow forging, that can only be done by the lost wax method, and the high-quality ceramic core is the best inner core material for the lost wax casting, which can still remain stable when casting the metal, and can be easily dissolved by the chemical process after the casting is cooled, leaving the required air passage in the blade.

First of all, the mold is placed in the clay liquid and rotated, so that it evenly wraps any part of the model, so that it can be considered qualified.

Then the model is added to a special bellows, sprayed with porcelain clay on the surface to form a thick shell, the casting model after wrapping the clay, and then air-dried, and then heated, the porcelain clay wrapped outside the casting model is fired into a ceramic model, and at the same time, the beeswax inside is discharged to form a casting cavity.

Finally, the produced blades also need to be X-rayed, and each blade is tested from multiple angles to prevent any defects. ”

Although Claire said it very simply, it was all dry goods, and Liu Lang firmly kept these words in mind, which has involved the process of the engine, which belongs to the level of "not being secret".

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