Chapter five hundred and seventy-eight Professor Claire's private goods
"Jimmy, Bob, you know the structure of car engines very well, so let me ask you a little question about aircraft engines. Of course, this is not a test for you two. If you know it, answer it. If you don't know, forget it!"
Claire walked up to the huge engine and pointed at the fan-like thing.
"Do you know what this is?"
Bob looked at it without saying a word. Of course he knew that this thing was a fan. The thrust of the aircraft was generated by the fan. The first-generation jet aircraft had such parts, but it was called a propeller engine. Obviously, the one in front of him
The fan is more precise and the blades are densely packed
Smooth as a knife. Today's power systems are all internal combustion type. The output power is much higher. The thrust generated by the strong airflow hitting the blades can blow the car away. Ordinary materials simply cannot withstand this.
The power, at least in terms of material, has been improved by an unknown amount.
"This should be an airplane fan, but it's different from an ordinary fan. It should be a turbofan! As for the others, I don't know."
Liu Lang replied that he was not a god and did not have the ability to predict the future. He had very little contact with relevant materials about aircraft engines. He had only seen some rough information in the library and had not studied it. Liu Lang also knew nothing about it.
"I don't know, okay, then I'll teach you two a lesson!
This is indeed called a turbofan, developed from a turboprop jet engine. The main feature of this turbofan is the large area of the first stage compressor, which is also used as an air propeller to push part of the inhaled air backward through the periphery of the jet engine.
The part of the engine core where the air passes is called the inner duct, and the outer part of the core where only the fan air passes is called the outer duct.
The exhaust speed of the turboprop engine is too low and the thrust is limited, so the efficiency of the jet engine must be improved. The efficiency of the engine includes two parts: thermal efficiency and propulsion efficiency. By increasing the temperature of the gas in front of the turbine and the boost ratio of the high-pressure compressor, it can
Improve thermal efficiency. Because of high temperature and high density, gas contains more energy."
Claire was eloquent, and he was very happy because it was rare to hear Liu Lang say that he didn't know how to do it.
"This is the principle of a turbine engine! Then these turbofans must be very different from the previous propeller fans!"
Liu Lang asked again.
"Of course, the air flow from the turbine can blow down a house. If it hits ordinary steel, it will be broken into pieces in less than half a year...Okay, today I will tell you about this turbine.
The construction of the fan!”
Claire became interested and started talking.
"The structure of a turbine blade is mainly composed of four parts: the blade crown, the blade body, the edge plate, and the blade root.
This is the blade shroud. In order to improve turbine efficiency, a shroud structure similar to an edge plate is often used on the upper end of the blade. Its function is to reduce air leakage from the blade tip from the blade basin to the blade back, reduce secondary losses, and improve turbine efficiency.
; Friction between the crowns of adjacent leaves can absorb vibration energy
amount, playing a vibration-absorbing effect; the crowns of the rotor blades of the same stage are pressed against each other, which can enhance the rigidity of the blades and improve their vibration resistance; the crowned blades can adopt a thin blade type that is more beneficial to aerodynamics. Currently, commonly used
The leaf crown shapes are mainly parallelogram and zigzag leaf crowns.
The main function of the blade is to realize the aerodynamic characteristics of the blade. The cross-sectional shapes of different heights of the blade are selected through aerodynamic design. An airflow channel is formed between the blades of adjacent blades in the circumferential direction, allowing high-temperature and high-pressure gas to flow through and expand to perform work.
; At the same time, the blade profile also has the function of adjusting the direction of the airflow to ensure uniform axial speed when the airflow enters the exhaust system.
The main function of the edge plate is to form an independent airflow channel to ensure that high-temperature gas does not flow into the turbine disc, 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.
, generally adopts a square structure, and the upper and lower parts are connected through the transition section, the blade body, and the blade root respectively. The blade edge plates of the same-stage rotor form a closed annular structure.
The blade root's main function is to connect the blades and the wheel disk in order to transmit power to the rotor shaft connected to the wheel disk. The upper part of the blade root and the part connected to the edge plate is called the extension root. The lower end of the blade root is connected to the turbine disk.
The parts generally use fir tree-shaped tenons. The advantages are: the circumferential size of the tenons
Smaller, more blades can be installed on the rim, resulting in high output power; multiple tooth surfaces transmit force, strong load-bearing capacity, and large safety margin; large contact area is conducive to heat dissipation and friction and vibration reduction; clearance fit,
It can expand freely after being heated, which can reduce thermal stress; it is easy to disassemble and assemble, etc."
The two of them listened very carefully, and Bob took out a piece of paper from his bag and took notes. This was Professor Claire's private property, and not everyone could learn it.
Of course Liu Lang didn't need paper and pen, his brain was equivalent to a computer. Bob remembered it very carefully, but he felt it was nothing. Professor Claire just introduced the composition, which was equivalent to a noun explanation, and was of little use to the essence.
"I think this kind of blade is very special and unique in structure, and the material is also very tough. Such a thin blade can easily become distorted when rotating at extremely high speeds. Professor, how are the blades of this engine made?"
Liu Lang asked pretending to touch the sharp blade.
"You asked a very professional question. This kind of blade is a typical free-form surface part. When processing such parts, there is a characteristic, that is, it must be thin, but it will produce a result, that is, it is easy to deform during processing, so the material is
It has to be very strict. Generally speaking, the material is stainless steel, but this is not ordinary stainless steel, Monel, INEL, titanium and nickel-based difficult-to-machine alloy materials!"
Claire replied.
"Oh, Monel, an alloy of titanium and nickel!"
Liu Lang wrote it down.
"Professor, you said that these alloys are very hard materials and difficult to process, but this kind of blade is extremely precise, which will put forward higher requirements for the processing technology and processing tools. You
Do you know?"
Liu Lang asked again.
"Haha, Jimmy, this kind of question doesn't trouble me. Okay, let me briefly explain this question.
In the processing of blades, the difficulties in blade processing include the following three aspects: milling of the surrounding area, processing of blade roots, and milling of tie holes... And these blades are all hollow, so this casting method is very difficult.
of.
For hollow forging, only the lost wax method can be used, and a high-quality ceramic core is the best inner core material for lost wax casting. It can still remain stable when casting metal, and can be easily passed through chemical processes after the casting is cooled.
Dissolve, leaving the required air channels in the leaves.
First, place the mold in the clay liquid and rotate it so that it evenly covers any part of the model, only then can it be considered qualified.
Then the model is added to a special bellows, and porcelain clay is sprayed on the outside to form a thick shell. The casting model is wrapped in clay and then air-dried. Then it is heated, and the porcelain clay wrapped on the outside of the casting model is fired into a ceramic model.
At the same time, the beeswax inside is discharged to form a casting cavity.
Finally, the produced blades also need to undergo X-ray inspection, and each blade must be inspected from multiple angles to prevent any defects."
Although Claire's words were very simple, they were all practical information. Liu Lang kept these words firmly in his heart. This already involves the craftsmanship of the engine and is a level that "cannot be taught secretly".