A brief history of aerodynamic development
The earliest study of aerodynamics can be traced back to various speculations about the forces that birds or projectiles are subjected to during flight and the ways in which the forces act. /kloc-In the late 7th century, the Dutch physicist Huygens first estimated the resistance of an object moving in the air; 1726 Newton applied the principle of mechanics and deductive method to draw the conclusion that the force on an object moving in the air is directly proportional to the square of its velocity, the characteristic area of the object and the density of the air. This work can be regarded as the beginning of the classical theory of aerodynamics.
1755, the mathematician Euler proposed a differential equation to describe the motion of inviscid fluid, namely Euler equation. These dynamic differential equations can be integrated under certain conditions, and the results obtained are of great practical value. /kloc-In the first half of the 9th century, Navid of France and Stokes of Britain put forward a motion equation describing the conservation of momentum of viscous incompressible fluid, which was later called Navid-Stokes equation.
By the end of 19, the foundation of classical fluid mechanics has been formed. Since the 20th century, with the rapid development of aviation, aerodynamics has developed from fluid mechanics and formed a new branch of mechanics.
The primary problem to be solved in aviation is how to obtain the lift required by the aircraft, reduce the drag of the aircraft and improve its flight speed. It is necessary to study the generation and law of force when an aircraft moves relative to the air theoretically and practically. 1894, Lanchester, England, first put forward the circulation theory of infinite-wingspan wing or airfoil to generate lift, and the vortex theory of finite-wingspan wing to generate lift. But Lanchester's idea didn't get widespread attention at that time.
During the period of1901~1910, Kuta and Zhukovsky independently put forward the theory of circulation and lift of airfoil, and gave the mathematical form of lift theory, and established the theory of two-dimensional wing. 1904, Planter of Germany published the famous low-speed flow boundary layer theory. The theory points out that the governing equation can have different simplified forms in different flow regions.
The boundary layer theory has greatly promoted the development of aerodynamics. Pelant also systematized the theory of finite-span three-dimensional wings and gave its mathematical results, thus establishing the theory of lift line of finite-span wings. However, it cannot be applied to stall, sweep angle and small aspect ratio. 1946 The theory of low aspect ratio wing was put forward by Jone of America. Using this theory and boundary layer theory, the pressure distribution and surface friction resistance on the wing can be calculated accurately enough.
The rapid development of modern aviation and jet technology makes the flight speed increase rapidly. In the case of high-speed motion, in order to correctly understand and solve the problems in high-speed aerodynamics, it is necessary to combine fluid mechanics with thermodynamics. During the period of 1887 ~ 1896, the Austrian scientist Mach pointed out that the propagation characteristics of the disturbance caused by projectiles are fundamentally different in different flows less than or greater than the speed of sound.
In high-speed flow, the ratio of velocity to local sound velocity is an important dimensionless parameter. 1929, the German aerodynamist Akelet first associated this dimensionless parameter with Mach's name. Ten years later, Mach, a characteristic parameter, was widely used in gas dynamics.
The propagation of small disturbances in supersonic flow will be superimposed to form a finite jumping shock wave. Shock waves also exist in many practical supersonic flows. When the airflow passes through the shock wave flow field, the parameters suddenly jump, the entropy increases, and the total energy remains unchanged.
1870, British scientist Rankin, 1887, French scientist Xu Hongniu independently established the relationship that airflow should meet when passing through the shock wave, which provided correct boundary conditions for the mathematical treatment of supersonic flow field. 1925, Akelet put forward the theory of two-dimensional linear mechanical wing, and then the theory of three-dimensional wing linearization appeared correspondingly. These linear theories of supersonic flow have successfully solved the influence of small disturbances in flow.
When the flight speed or airflow speed approaches the sound speed, the aerodynamic performance of the aircraft changes sharply, the drag increases sharply, and the lift drops sharply. The maneuverability and stability of aircraft have deteriorated extremely, which is the famous sound barrier in aviation history. The appearance of large thrust engine broke through the sound barrier, but it did not solve the complex transonic flow problem well. It was not until the 1960s that the research on transonic flow was paid more attention and developed greatly due to the development of transonic cruise flight, maneuvering flight and efficient jet engine.
The development of long-range missiles and artificial satellites has promoted the development of hypersonic aerodynamics. In 1950s and 1960s, the hypersonic inviscid flow theory and aerodynamic engineering calculation method were established. In the early 1960s, the numerical calculation of hypersonic flow also developed rapidly. By studying these phenomena and laws, high-temperature gas dynamics, high-speed boundary layer theory and non-balanced flow theory are developed.
It is necessary to study the multiphase flow of high temperature gas because of the ablation of aircraft surface materials and the mass ejection at high temperature. The development of aerodynamics has the characteristics of combining with many disciplines.
Another important aspect of aerodynamic development is experimental research, including the development of various experimental equipment such as wind tunnel and the development of experimental theory, method and testing technology. The world's first wind tunnel was built in 187 1 year, located in Wehnam, England. Up to now, there are dozens of wind tunnels suitable for various simulation conditions, purposes, uses and various measurement methods, and the contents of wind tunnel experiments are extremely extensive.
Since 1970s, the rapid development of laser technology, electronic technology and computer has greatly improved the experimental level and computational level of aerodynamics, and promoted the study of highly nonlinear problems and complex structure flows.
In addition to the above-mentioned development of aerospace industry, the development of aerodynamics has been promoted. Since 1960s, due to the development of transportation, construction, meteorology, environmental protection, energy utilization and other aspects, sub-disciplines such as industrial aerodynamics have emerged.
Research content of aerodynamics
Usually, the research contents of aerodynamics are the variation laws of gas velocity, pressure and density in the flow field of aircraft, missiles and other aircraft under famous flight conditions, aerodynamic forces such as lift and resistance and their variation laws, physical and chemical changes between gas medium or gas and aircraft, and heat and mass transfer laws. In this sense, aerodynamics can be divided into two categories:
Firstly, according to the speed range of fluid movement or the flight speed of aircraft, aerodynamics can be divided into low-speed aerodynamics and high-speed aerodynamics. Usually, the speed of 400 km/h is roughly used as the dividing line. In low-speed aerodynamics, gas medium can be regarded as incompressible, and the corresponding flow is called incompressible flow. When the velocity is greater than this, the compressibility of gas and the change of thermodynamic characteristics of gas must be considered. This flow corresponding to high-speed aerodynamics is called compressible flow.
Secondly, according to whether the viscosity of gas medium must be considered in flow, aerodynamics can be divided into ideal aerodynamics (or ideal aerodynamics) and viscous aerodynamics.
In addition to the above classification, aerodynamics has some marginal branches. Such as rarefied gas dynamics and high temperature gas dynamics.
In low-speed aerodynamics, the change of medium density is very small and can be regarded as a constant. The basic theories used are inviscid two-dimensional and three-dimensional potential flow, airfoil theory, lifting line theory, lifting surface theory and low-speed boundary layer theory. For subsonic flow, inviscid potential flow obeys nonlinear elliptic partial differential equation. The main theories and approximate methods to study this kind of flow include small disturbance linearization method, Planter-Graue separation rule, Carmen- Qian Xuesen formula, hodograph method and compressible boundary layer theory in viscous flow. For supersonic flow, the equation of inviscid flow is nonlinear hyperbolic partial differential equations.
In supersonic flow, the basic research contents include compression wave, expansion wave, shock wave, Plante-Meyer flow, conical flow and so on. The main theoretical treatment methods are supersonic small disturbance theory, characteristic line method and high-speed boundary layer theory. Transonic inviscid flow can be divided into two parts: external flow and internal flow, and the flow changes are complex. The governing equation of flow is a nonlinear mixed partial differential equation, which is difficult to solve theoretically.
The main characteristics of hypersonic flow are high Mach number and large energy. In hypersonic flow, real gas effect and the interaction between shock wave and boundary layer become more important. Hypersonic flow is divided into inviscid flow and hypersonic viscous flow.
Industrial aerodynamics mainly studies the interaction between wind in the atmospheric boundary layer and various structures and human activities, as well as the characteristics of wind in the atmospheric boundary layer, the effect of wind on buildings, the mass transfer caused by wind, the effect of wind on transport vehicles and the utilization of wind energy, and