Due to its high development difficulty, high technical content and high industrial returns, the aero-engine is known as the “golden crown†of modern industry. The newly established China Aero Engine Research Institute has signed scientific and technological innovation cooperation agreements with many domestic universities and scientific research institutions to jointly carry out research on aeroengine basic and applied technologies.
On December 28th, China Aviation Engine Research Institute was established in Beijing. The institute was established by the China Aviation Engine Group, which was just established four months ago. It aims to promote the improvement of China's aero-engine independent innovation capability and provide important support for the major research and management of aerospace engines and gas turbines.
On August 28, at the time of the establishment of China Aviation Engine Group Corporation, General Secretary of the CPC Central Committee, President of the State, Chairman of the Central Military Commission Xi Jinping and Premier of the State Council Li Keqiang all made important instructions.
Why did an aero-engine company establish a state with such high standards? Recently, the Science and Technology Daily reporter interviewed Wang Ya-nan, editor-in-chief of Aviation Knowledge magazine, on this issue.
"This is determined by the status of the aero engine. Aeroengine is a technology that draws the limit of classical mechanics in engineering applications. It is an important indicator to measure a country's comprehensive scientific and technological level, the basic strength of science and technology industry and comprehensive national strength." Wang Yanan said.
Wang Yanan believes that the establishment of China Aviation Engine Group Corporation transmits an important signal that China hopes to prepare scientifically sufficient conditions for the development of advanced aerodynamic systems from the top-level structure.
Classical mechanics approaches the limit in engineering applicationsFor a long time, some people have not understood why China’s creation of the Shenzhou spacecraft and the production of the æ¼-20 fighters can not create advanced aviation engines. First understand the principles of aero engines and what kind of technology is this.
Modern aviation jet engines are the same as four-stroke internal combustion engines. The four-stroke internal combustion engine has four working stages of intake, compression, combustion and exhaust, which are realized by reciprocating movement of the piston.
"For the aero jet engine, these four phases of work still exist, except that the reciprocating pistons and cylinders are replaced by a set of rotor systems consisting of coaxial blades, and the reciprocating motion is completely replaced by a seemingly simpler rotational motion. Wang Ya-nan analyzed the working principle of the engine.
Originally, the reason for the engine to generate power is as follows: the intake air is realized through the intake passage, and the air is pressurized by the high-speed rotation of the compressor; the pressurized air is sent to the annular combustion chamber, and the fuel is mixed and ignited to This pushes the turbine to rotate at high speed; finally, the energy is transferred to the compressor and discharged backward through the nozzle to generate a strong forward thrust.
In short, an aero-engine is a thermal machine that powers an aircraft. It needs to work under high temperature, high pressure, and high-speed rotation, and has high requirements for development.
How high is the temperature? The current advanced aero engine operating temperature is 1850K, which greatly exceeds the melting point of the engine's turbine blade nickel-based alloy.
How much pressure is there? The pressure of the engine compressor after pressurization is up to tens of atmospheres, which is equivalent to the pressure at the bottom of the Three Gorges Dam after four or five waters are filled.
How fast is the rotation? The rotor rotates tens of thousands of revolutions per minute, and the centrifugal force on the tip of the blade is equivalent to the pulling force of a 40-ton truck.
High temperature, high pressure and high speed can be solved by some technical means alone. For example, spacecraft and rockets can cover heat-insulating tiles at high temperatures to solve high-temperature problems. Ground and surface power can make the engine bigger and solve pressure and strength problems. Disposable products such as missile power and rocket power do not. Need to consider long life, some problems will be solved, and finally burned or no longer used.
However, the aero-engine is not the same, and its development has the requirements of “small size, light weight, long life and reusableâ€, which means that the difficulty is multiplied. Designing an aero engine is about maximizing performance under these demanding constraints.
"It can be said that the aero engine is a technology that draws the limit of classical mechanics in engineering applications." Wang Yanan said.
The material does not melt at 1850K without deformation and does not break.Manufacturing an engine involves countless technical fields.
“Overall design, advanced metal/non-metallic materials, advanced processing and manufacturing, aerodynamics under high temperature and high pressure conditions, comprehensive test and inspection, advanced technology project management...†Wang Yanan casually lists so many technical fields.
These technical fields are not only complicated, but also cannot be rushed for success. They all need long-term accumulation.
Only one material technology is dazzling.
One of the most important technical indicators to see whether the engine is advanced or not is to look at its thrust-to-weight ratio, which is the ratio of the engine's thrust divided by its weight.
Take the Su-27 AL-31 turbofan engine as an example. Its maximum thrust is 12.5 tons, and two AL-31s can propel the Su-27 to fly at more than 2 times the speed of sound. The AL-31 has a fan diameter of less than 900 mm and a turbine diameter of less than 300 mm. According to the basic physics principle, the forces interact, which means that the fan and turbine of such a small size are in turn subject to a force of 12.5 tons.
The engine must propel the aircraft to fly at 2 times the speed of sound, and the components must withstand the extremely harsh high temperature and high pressure tests.
The more advanced the aero engine, the greater the thrust and the lighter the weight. To achieve this goal, you have to try to increase the temperature before the turbine – an important indicator of thermal efficiency.
The state-of-the-art aerospace engine has a pre-turbine temperature of 1850K, which greatly exceeds the melting point of steel. The material used to make the turbine blades must withstand the high temperatures above the melting point temperature, and at the same time the pressure of the bottom of the Three Gorges Dam after several times of water filling, with a sustained effect of strong centrifugal force at a speed of tens of thousands of revolutions per minute. In such a harsh environment, the materials used in the engine must be: not melted, deformed, and not broken.
"In a word, if the materials industry can't get the best high-temperature materials, the performance of the engine will not go up." Wang Yanan said.
Increased thrust and effort to reduce weight. To do this, you can only reduce the total number of parts, or make the parts small enough, thin enough, and the performance can not be reduced, which requires the overall design technology and materials to be quite strong.
The seventh generation of aviation engines has begun pre-researchJet aircraft engines have evolved to date and have been through four generations.
The first generation of jet engines appeared in the 1940s. It is mainly a turbojet engine, represented by J57 in the United States and RD-9B in the former Soviet Union. Its thrust-to-weight ratio is 3-4, and the pre-turbine temperature is 1200-1300K.
The second generation of jet engines appeared in the 1960s, mainly afterburning turbojet engines and turbofan engines. It is represented by the British Spey MK202 and the US TF30 engine. The thrust ratio is 5-6, and the turbine front temperature is 1400-1500K. ;
The third-generation air jet engine that emerged in the 1970s was an afterburner turbofan engine, represented by the US F100, F110, F404, European RBl99, M88-3, Soviet RD-33 and AL-31F engines. The thrust-to-weight ratio reaches 8, and the pre-turbine temperature is 1600-1700K;
Currently widely used is the fourth generation jet engine, which is characterized by a high thrust-to-weight ratio turbofan engine, represented by the US F119 and the European EJ200 engine, with a thrust-to-weight ratio of 9.5-10 and a pre-turbine temperature of 1850-2000K.
Wang Yanan believes that the next-generation jet engine will adopt the concept of variable-cycle turbofan engine, which uses advanced materials extensively. The temperature before the turbine is expected to exceed 2200K, and the thrust-to-weight ratio is expected to reach 12-15.
According to the data, after 2010, relying on its strong technical research and development capabilities, the United States has launched the development of the sixth generation of aero-engines, and the estimated weight-to-weight ratio will reach 16-18, or even higher. Phased results have been achieved, and the seventh-generation aero engine has also been pre-researched.
“The new generation of aerospace engines demand higher requirements in terms of manufacturing cost, maintainability, operational economy and life cycle cost, challenging the highest level of human turbine engine technology and representing a country’s industrial R&D and manufacturing. The commanding heights of ability." Wang Yanan said.
"Compared with the traditional powers of the United States, Britain, France, Russia and other aerospace engines, China's foundation and experience are still lacking, but we are making rapid progress." Wang Yanan believes.
The domestic Taihang engine, also known as the turbofan 10 series engine, is the third-generation large-scale military aviation turbofan engine produced in China. Pre-research in 1978, project was established in 1987, and design review and assessment was completed on December 28, 2005, which lasted for 27 years.
"The successful development of the Taihang turbofan engine allowed China to complete the entire process of independent research and development, production and improvement of advanced military jet engines for the first time, and accumulated experience and prepared conditions for the subsequent development of the engine industry." Wang Yanan said.
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Aircraft Heaven and Bernoulli Theorem
In the earth's gravity environment, items that are lighter than air can be lifted freely, and vice versa. And if there is wind, this wind can blow away items that are heavier than air.
This wind is the flowing air, also known as the airflow.
An aircraft is an air-heavy aircraft, and naturally requires a force to overcome its own gravity and achieve its purpose of pushing it into the air. When the aircraft is flying in the air, it will generate aerodynamic forces acting on the aircraft. The aircraft is powered by this aerodynamic flight.
The engine is the airflow that is used to push the aircraft to take off.
In 1738, Daniel Bernoulli, the father of fluid mechanics, discovered that in a fluid system, such as airflow or water, the faster the flow rate, the lower the pressure generated by the fluid. This principle, which describes the relationship between flow velocity and pressure in a fluid, is called the Bernoulli's theorem.
The basic content of the Bernoulli theorem: When the fluid flows in a pipe, the pressure is small in the place where the flow rate is large, and the pressure is large in the place where the flow rate is small.
The lift of the aircraft depends on the airflow. The airflow is divided into upper and lower parts by the wing. Due to the up-and-down asymmetry of the cross-section of the wing, the airflow over the wing is longer and the speed is higher in the same time; the lower distance is shorter and the speed is small. Since the pressure at the position where the flow rate is larger in the gas and the liquid is smaller, there is a pressure difference between the upper and lower surfaces of the wing, which causes an upward lift.
This powerful airflow is generated by the relative speed that the engine gives to the aircraft.
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