Aerodynamics is a branch of dynamics concerned with the study of the motion of air. It is a sub-field of fluid and gas dynamics, and the term "aerodynamics" is often used when referring to fluid dynamics. Early records of fundamental aerodynamic concepts date back to the work of Aristotle and Archimedes in the 2nd and 3rd centuries BC, but efforts to develop a quantitative theory of airflow did not begin until the 18th century. In 1726 Isaac Newton became one of the first aerodynamicists in the modern sense when he developed a theory of air resistance which was later verified for low flow speeds. Air resistance experiments were performed by investigators throughout the 18th and 19th centuries, aided by the construction of the first wind tunnel in 1871. In his 1738 publication Hydrodynamica, Daniel Bernoulli described a fundamental relationship between pressure, velocity, and density, now termed Bernoulli's principle, which provides one method of explaining lift. Aerodynamics work throughout the 19th century sought to achieve heavier-than-air flight. George Cayley developed the concept of the modern fixed-wing aircraft in 1799, and in doing so identified the four fundamental forces of flight - lift, thrust, drag, and weight. The development of reasonable predictions of the thrust needed to power flight in conjunction with the development of high-lift, low-drag airfoils paved the way for the first powered flight. On December 17, 1903, Wilbur and Orville Wright flew the first successful powered aircraft. The flight, and the publicity it received, led to more organized collaboration between aviators and aerodynamicists, leading the way to modern aerodynamics. Theoretical advances in aerodynamics were made parallel to practical ones. The relationship described by Bernoulli was found to be valid only for incompressible, inviscid flow. In 1757, Leonhard Euler published the Euler equations, extending Bernoulli's principle to the compressible flow regime. In the early 19th century, the development of the Navier-Stokes equations extended the Euler equations to account for viscous effects. During the time of the first flights, several investigators developed independent theories connecting flow circulation to lift. Ludwig Prandtl became one of the first people to investigate boundary layers during this time.
Antiquity to the 19th century
Theoretical foundations Although the modern theory of aerodynamic science did not emerge until the 18th century, its foundations began to emerge in ancient times. The fundamental aerodynamics continuity assumption has its origins in Aristotle's Treatise on the Heavens, although Archimedes, working in the 3rd century BC, was the first person to formally assert that a fluid could be treated as a continuum. Archimedes also introduced the concept that fluid flow was driven by a pressure gradient within the fluid. This idea would later prove fundamental to the understanding of fluid flow. In 1687, Newton's Principia presented Newton's laws of motion, the first complete theoretical approach to understanding mechanical phenomena. In particular, Newton's second law, a statement of the conservation of momentum, is one of three fundamental physical principles used to obtain the Euler equations and Navier-Stokes equations. In 1738, the Dutch-Swiss mathematician Daniel Bernoulli published Hydrodynamica, in which he described the fundamental relationship between pressure and velocity, known today as Bernoulli's principle. This states that the pressure of a flowing fluid decreases as its velocity increases and as such was a significant early advance in the theory of fluid dynamics, and was first quantified in an equation derived by Leonhard Euler. This expression, often called Bernoulli's Equation, relates the pressure, density, and velocity at two points along a streamline within a flowing fluid as follows:
v 1 2 2 + p 1 ρ = v 2 2 2 + p 2 ρ {\displaystyle {v_{1}^{2} \over 2}+{p_{1} \over \rho }={v_{2}^{2} \over 2}+{p_{2} \over \rho }}
Bernoulli's Equation ignores compressibility of the fluid, as well as the effects of gravity and viscous forces on the flow. Leonhard Euler would go on to publish the Euler equations in 1757, which are valid for both compressible and incompressible flows. The Euler equations were extended to incorporate the effects of viscosity in the first half of the 1800s, resulting in the Navier-Stokes equations.
Studies of air resistance
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