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Chapter 1 Introduction This chapter mainly introduces the definition of aerodynamics�� research objects and tasks�� research methods and classifications�� and the development history of aerodynamics�� especially the leading role played in the development of modem aircraft. Learning points: (1) Definition�� research object�� research method�� research content�� and classification of aerodynamics. (2) The development history of aerodynamics and its leading role in the development of modem aircraft. 1.1 Aerodynamics Research Tasks There are five basic material forms in nature�� including solid state�� liquid state�� gas state�� plasma state�� and ultra-dense state. Among them�� solid corresponds to solid�� liquid corresponds to liquid�� and gas corresponds to gas. These three forms of matter are common and are jointly determined by the internal microstructure of matter�� molecular thermal motion�� and the force between molecules. The phase diagram of the object is shown in Fig. 1.1. From the perspective of macroscopic force�� the force state of liquid and gas in a static state is the same (almost unable to withstand tensile and shear forces)�� so liquid and gas are called fluids. According to the definition�� mechanics is the subject of studying the laws of equilibrium and mechanical motion of objects and their applications. Therefore�� solid mechanics is the subject of studying the laws of solids in equilibrium and mechanical motion and their applications�� while fluid mechanics is the subject of studying the laws of fluids in equilibrium and mechanical motion and their applications and applied disciplines. Aerodynamics is a branch of fluid mechanics. It is a discipline that studies air in equilibrium and the laws of mechanical motion and its applications. Aerodynamics is also a branch of physics�� which mainly studies the laws of motion and force of air (or objects) when there is relative motion between objects and air. Traditional aerodynamics refers to the aerodynamics of aircraft�� especially the aerodynamics of ordinary airplanes. Part of the force of the air on a moving aircraft is reflected in the lift (perpendicular to the flying direction of the aircraft)�� which acts on the aircraft; the other part is reflected in drag (opposite to the flying direction)�� which hinders the aircraft; and another part is caused by the resultant moment generated by the distributed pressure acting on the surface of the aircraft that controls the attitude of the aircraft. When people study aerodynamics�� they often use the principle of relative flight to equate the movement of the aircraft through the air as the motion of the aircraft moving around the aircraft without moving the air. Using this principle�� study the aerodynamic behavior of an aircraft when it moves in a uniform straight line at a certain speed in still air. The aerodynamic force experienced when bypassing the aircraft is equivalent�� as shown in Fig. 1.2. Relative to the principle of flight�� it provides convenience for the research of aerodynamics�� which is the basis of aerodynamics experiments. During experimental research�� people can fix the aircraft model�� artificially create a straight and uniform airflow through the model�� in order to observe the flow phenomenon�� measure the aerodynamic force received by the model�� conduct aerodynamic experimental research�� and let the airflow in the wind tunnel test. Flow is easier to achieve than moving objects (as shown in Fig. 1.3). In flight mechanics�� the speed relative to the aircraft is called airspeed (incoming flow speed)�� which is used to calculate aerodynamics; and the speed relative to the ground is called ground speed�� which is used to calculate the flying distance of the aircraft. Fig. 1.1 Phase diagram of object When there is no crosswind�� the airspeed and ground speed of the aircraft are equal and opposite; but when there is a crosswind�� the two are different. As a classic textbook�� the main content of aerodynamics foundation includes aerodynamics and dynamics foundation. In low-speed flow�� incompressible ideal fluid (inviscid fluid) two-dimensional and three-dimensional potential flow�� thin wing theory�� lift line and surface theory�� flow around swept wings�� etc. Viscous fluid dynamics equations�� near-wall boundary layer theory�� boundary layer separation�� resistance of circumfluence objects�� multi-section airfoil circumfluence�� etc. In the subsonic flow�� the full-velocity potential function of the compressible ideal potential flow is a nonlinear elliptic partial differential equation�� the theory of perturbation linearization�� the Prandtl��Glauert rule�� and the Carmen��Qian Xuesen formula. Fig. 1.2 Relative flight principle Fig. 1.3 Wind tunnel test In supersonic flow�� small perturbation linear hyperbolic partial differential equations of compressible ideal potential flow velocity potential function�� compression wave�� expansion wave�� shock wave�� Prandtl-Meyer flow�� e