Fluid Mechanics(history of fluid mechanics)

Introduction

A fluid cannot resist a shear stress by a static deflection and it moves and deforms continuously as long as the shear stress is applied. Fluid mechanics is the study of fluids either in motion (fluid dynamics) or at rest (fluid statics). Both liquids and gases are classified as fluids. There is a theory available for fluid flow problems, but in all cases it should be backed up by experiment. It is a highly visual subject with good instrumentation. Since the earth is 75% covered with water and 100% with air, the scope of fluid mechanics is vast and has numerous applications in engineering and human activities. Examples are medical studies of breathing and blood flow, oceanography, hydrology, energy generation. Other engineering applications include: fans, turbines, pumps, missiles, airplanes to name a few. The basic equations of fluid motion are too difficult to apply to arbitrary geometric configurations. Thus most textbooks concentrate on flat plates, circular pipes, and other simple geometries. It is possible to apply numerical techniques to complex geometries, this branch of fluid mechanics is called computational fluid mechanics (CFD). Our focus, however, will be on theoretical approach in this course. Viscosity is an internal property of a fluid that offers resistance to flow. Viscosity increases the difficulty of the basic equations. It also has a destabilizing effect and gives rise to disorderly, random phenomena called turbulence.

History of fluid mechanics

Ancient civilization had enough knowledge to solve certain flow problems, e.g. sailing ships with oars, irrigation systems.

• Archimedes (285 – 212 B.C.) postulated the parallelogram law for addition of vectors and the laws of buoyancy and applied them to floating and submerged objects.
• Leonardo da Vinci (1452 – 1519) stated the equation of conservation of mass in one‐dimensional steady‐state flow. He experimented with waves, jets, hydraulic jumps, eddy formation, etc.
• Edme Mariotte (1620 – 1684) built the first wind tunnel and tested models in it.
• Isaac Newton (1642 – 1727) postulated his laws of motion and the law of viscosity of linear fluids, now called newtonian. The theory first yield the frictionless assumption which led to several beautiful mathematical solutions.
• Leonhard Euler (1707 – 1783) developed both the differential equations of motion and their integral form, now called Bernoulli equation.
• William Froude (1810 – 1879) and his son developed laws of model testing and Lord Rayleigh (1842 – 1919) proposed dimensional analysis.
• Osborne Reynolds (1842 – 1912) published the classic pipe experiment and showed the importance of the dimensionless Reynolds number, named after him.
• Navier (1785 – 1836) and Stokes (1819 – 1903) added newtonian viscous term to the equation of motion, the fluid motion governing equation, i.e., Navier‐Stokes equation is named after them.
• Ludwig Prandtl (1875 – 1953) pointed out that fluid flows with small viscosity, such as water flows and airflows, can be divided into a thin viscous layer (or boundary layer) near solid surfaces and interfaces, patched onto a nearly inviscid outer layer, where the Euler and Bernoulli equations apply.