History of Fluid Mechanics

History of Fluid Mechanics

Fluid Mechanics In Everyday Life

There is air around us, and there are rivers and seas near us. ‘The flow of a river never ceases to go past, nevertheless, it is not the same water as before.Bubbles floating along on the stagnant water now vanish and then develop but have never remained.’ So stated Chohmei Kamo, the famous thirteenth-century essayist of  Japan,  in the prologue of  Hohjohki, his collection of essays.  In this way,  the air and the water of rivers and seas  are  always moving. Such a movement of gas or liquid (collectively called ‘fluid’) is called the ‘flow’, and the study of this is ‘fluid mechanics’. While the flow of the air and the water of rivers and seas are flows of  our concern, so also are the flows of water, sewage and gas in pipes, in irrigation canals, and around rockets, aircraft, express trains, automobiles and boats.And so  too is the resistance which acts on such flows.

Throwing baseballs and hitting golf balls are all  acts  of  flow.Furthermore,  the movement of people on the platform of a railway station or at the intersection of streets can be regarded as forms of flow. In a wider sense, the movement of social phenomena,  information or history could be regarded as a flow, too. In this way, we are in so close a relationship to flow that the  ‘fluid mechanics’ which studies flow is really a very familiar thing to us.

The Beginning of fluid mechanics

The science of flow has been classified into hydraulics, which developed from experimental studies, and hydrodynamics, which developed through theoretical studies. In recent years, however, both have merged into the single discipline called fluid mechanics.

Hydraulics developed as  a purely empirical science with practical techniques beginning in prehistoric times. As our ancestors settled to engage in farming and their hamlets developed into villages, the continuous supply of  a proper quantity of water and the transport of essential food  and materials posed the most important problems. In this sense, it is believed that hydraulics was born in the utilisation of water channels and ships. Prehistoric relics of irrigation canals were discovered in Egypt  and Mesopotamia, and it  has been confirmed that canals had been constructed more than 4000 years BC.

Water  in cities is  said to have begun in Jerusalem,  where  a  reservoir  to store water and  a masonry channel to  guide the water were constructed. Water canals were  also constructed in Greece and other places. Above all, however,  it  was  the  Romans who constructed channels throughout the Roman Empire. Even today their remains are still visible in many places in Europe .

The city water system in those days guided relatively clear water from far away to fountains, baths and public buildings. Citizens then fetched the water from water supply stations at high street corners etc. The quantity of water a day used by  a citizen in those days is said to be approximately  180litres.Today, the amount of water used per capita per day in an average household is said to be approximately 240 litres. Therefore, even about 2000 years ago, a considerably high level of cultural life occurred.

As  stated above, the history  of the city water system is very  old.  But  in the development process of city water systems, in order to transport water effectively, the shape and size of the water conduit had to be designed and its inclination  or supply pressure had to be adjusted to overcome friction with the  wall of the conduit.  This gave rise  to much invention and progress in overcoming hydraulic problems.

On the other  hand, the origin of  the ship is not clear,  but  it is easy to imagine the course of progress from log to raft, from manual  propulsion  to sails, and from river to ocean navigation.  The Phoenicians and Egyptians built  huge, excellent ships.  The relief work , which was made  about 2700~c, clearly depicts a  ship which existed at that  time.  The Greeks also left various records  of ships. One of them is a beautiful picture of  a  ship depicted on an old Grecian vase. As  these objects indicate,  it was by progress in shipbuilding and also navigation techniques that allowed much  fundamental hydraulic knowledge to  be accumulated.Before proceeding to describe the development of  hydraulics,  the Renaissance  period  of Leonardo da Vinci, in particular, should be recalled.

Popularly  he  is  well  known  as  a  splendid  artist,  but  he  was  an  excellent scientist,  too.  He was so well  versed in  the  laws of  natural  science that  he stated  that  ‘a body  tries  to drop down onto the  earth  through  the  shortest path’,  and also that  ‘a body gives air the same force as the resistance which air gives the body’. These statements preceded Newton’s law of gravity and motion (law of action and reaction).

Particularly  interesting  in  the  history  of  hydraulics  is  Leonardo’s  note where a  vast  description  is  made  of  the  movement  of  water,  eddies, water waves, falling water, the destructive force of water, floating bodies, efflux and the flow in a tube/conduit  to hydraulic machinery.  As examples,is a sketch of the flow around an obstacle, and shows the development of vortices  in the  separation  region.  Leonardo was the first to find the least resistive ‘streamline’ shape.