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One of the first engineering problems humankind faced as cities were developed was the supply of water for domestic use and irrigation of crops. Our
urban lifestyles can be retained only with abundant water, and it is clear
from archeology that every successful civilization of prehistory invested in
the construction and maintenance of water systems. The Roman aqueducts,
some of which are still in use, are the best known examples. However, perhaps the most impressive engineering from a technical viewpoint was done
at the Hellenistic city of Pergamon in present-day Turkey. There, from 283 to
133 bc, they built a series of pressurized lead and clay pipelines (Fig. 1–9),
up to 45 km long that operated at pressures exceeding 1.7 MPa (180 m of
head). Unfortunately, the names of almost all these early builders are lost to
history.
The earliest recognized contribution to fluid mechanics theory was made
by the Greek mathematician Archimedes (285–212 bc). He formulated and
applied the buoyancy principle in history’s first nondestructive test to determine the gold content of the crown of King Hiero I. The Romans built great
aqueducts and educated many conquered people on the benefits of clean
water, but overall had a poor understanding of fluids theory. (Perhaps they
shouldn’t have killed Archimedes when they sacked Syracuse.)
During the Middle Ages, the application of fluid machinery slowly but
steadily expanded. Elegant piston pumps were developed for dewatering
mines, and the watermill and windmill were perfected to grind grain, forge
metal, and for other tasks. For the first time in recorded human history, significant work was being done without the power of a muscle supplied by a
person or animal, and these inventions are generally credited with enabling
the later industrial revolution. Again the creators of most of the progress
are unknown, but the devices themselves were well documented by several
technical writers such as Georgius Agricola (Fig. 1–10).
The Renaissance brought continued development of fluid systems and
machines, but more importantly, the scientific method was perfected and
adopted throughout Europe. Simon Stevin (1548–1617), Galileo Galilei
(1564–1642), Edme Mariotte (1620–1684), and Evangelista Torricelli
(1608–1647) were among the first to apply the method to fluids as they
investigated hydrostatic pressure distributions and vacuums. That work was
integrated and refined by the brilliant mathematician and philosopher, Blaise
Pascal (1623–1662). The Italian monk, Benedetto Castelli (1577–1644) was
the first person to publish a statement of the continuity principle for fluids. Besides formulating his equations of motion for solids, Sir Isaac Newton (1643–1727) applied his laws to fluids and explored fluid inertia and
resistance, free jets, and viscosity. That effort was built upon by Daniel
Bernoulli (1700–1782), a Swiss, and his associate Leonard Euler (1707–
1783). Together, their work defined the energy and momentum equations.
Bernoulli’s 1738 classic treatise Hydrodynamica may be considered the first
fluid mechanics text. Finally, Jean d’Alembert (1717–1789) developed the
idea of velocity and acceleration components, a differential expression of continuity, and his “paradox” of zero resistance to steady uniform motion
over a body.
The development of fluid mechanics theory through the end of the eighteenth century had little impact on engineering since fluid properties and
parameters were poorly quantified, and most theories were abstractions that
could not be quantified for design purposes. That was to change with the
development of the French school of engineering led by Riche de Prony
(1755–1839). Prony (still known for his brake to measure shaft power) and
his associates in Paris at the École Polytechnique and the École des Ponts
et Chaussées were the first to integrate calculus and scientific theory into
the engineering curriculum, which became the model for the rest of the
world. (So now you know whom to blame for your painful freshman year.)
Antonie Chezy (1718–1798), Louis Navier (1785–1836), Gaspard Coriolis
(1792–1843), Henry Darcy (1803–1858), and many other contributors to
fluid engineering and theory were students and/or instructors at the schools.
By the mid nineteenth century, fundamental advances were coming on
several fronts. The physician Jean Poiseuille (1799–1869) had accurately
measured flow in capillary tubes for multiple fluids, while in Germany
Gotthilf Hagen (1797–1884) had differentiated between laminar and turbulent flow in pipes. In England, Lord Osborne Reynolds (1842–1912) continued that work (Fig. 1–11) and developed the dimensionless number that
bears his name. Similarly, in parallel to the early work of Navier, George
Stokes (1819–1903) completed the general equation of fluid motion (with
friction) that takes their names. William Froude (1810–1879) almost singlehandedly developed the procedures and proved the value of physical model
testing. American expertise had become equal to the Europeans as demonstrated by James Francis’ (1815–1892) and Lester Pelton’s (1829–1908)
pioneering work in turbines and Clemens Herschel’s (1842–1930) invention
of the Venturi meter.
In addition to Reynolds and Stokes, many notable contributions were made
to fluid theory in the late nineteenth century by Irish and English scientists,
including William Thomson, Lord Kelvin (1824–1907), William Strutt, Lord
Rayleigh (1842–1919), and Sir Horace Lamb (1849–1934). These individuals investigated a large number of problems, including dimensional analysis,
irrotational flow, vortex motion, cavitation, and waves. In a broader sens their work also explored the links between fluid mechanics, thermodynamics, and heat transfer.
The dawn of the twentieth century brought two monumental developments.
First, in 1903, the self-taught Wright brothers (Wilbur, 1867–1912; Orville,
1871–1948) invented the airplane through application of theory and determined experimentation. Their primitive invention was complete and contained
all the major aspects of modern aircraft (Fig. 1–12). The Navier–Stokes equations were of little use up to this time because they were too difficult to solve.
In a pioneering paper in 1904, the German Ludwig Prandtl (1875–1953)
showed that fluid flows can be divided into a layer near the walls, the boundary layer, where the friction effects are significant, and an outer layer where
such effects are negligible and the simplified Euler and Bernoulli equations
are applicable. His students, Theodor von Kármán (1881–1963), Paul Blasius
(1883–1970), Johann Nikuradse (1894–1979), and others, built on that theory
in both hydraulic and aerodynamic applications. (During World War II, both
sides benefited from the theory as Prandtl remained in Germany while his
best student, the Hungarian-born von Kármán, worked in America.)
The mid twentieth century could be considered a golden age of fluid
mechanics applications. Existing theories were adequate for the tasks at
hand, and fluid properties and parameters were well defined. These supported a huge expansion of the aeronautical, chemical, industrial, and
water resources sectors; each of which pushed fluid mechanics in new
directions. Fluid mechanics research and work in the late twentieth century
were dominated by the development of the digital computer in America.
The ability to solve large complex problems, such as global climate modeling or the optimization of a turbine blade, has provided a benefit to our
society that the eighteenth-century developers of fluid mechanics could
never have imagined (Fig. 1–13). The principles presented in the following
pages have been applied to flows ranging from a moment at the microscopic scale to 50 years of simulation for an entire river basin. It is truly
mind-boggling.
Where will fluid mechanics go in the twenty-first century and beyond?
Frankly, even a limited extrapolation beyond the present would be sheer folly.
However, if history tells us anything, it is that engineers will be applying
what they know to benefit society, researching what they don’t know, and
having a great time in the process.
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