# Fluid Mechanics and Hydraulic Machines

It is evident that matter exists in two forms, namely fluid and non-fluid (or solid). A fluid is a substance which deforms continuously when subjected to shear forces. The deformation occurs at a finite rate and it can be determined by the applied shear force and fluid properties. The act of continuous deformation is called the flow. Thus, fluid may be defined as a substance which is capable of flowing and it includes liquids and gases.

A fluid does not have its own shape but it conforms to the shape of the container. The mass of a fluid has definite volume at particular temperature and pressure. A liquid is practically considered as incompressible (i.e., density remains constant), but it takes the shape of the container. If the container is of a larger volume, then it forms a free surface. Gases are highly compressible and it takes the shape of the containing vessel but it occupies the whole volume of the container without any free surface. The fluid flow analysis is carried out at macro-level by considering the fluid as a continuum. In this chapter, the basic concepts used in the analysis of fluid flow and the various engineering properties of fluids that are essential in the study of their behaviour are described.

The subject of fluid mechanics deals with the behaviour of the fluids at rest or in motion, as well as its interaction with solids or other fluids at the oundaries. Broadly, this subject is classified into statics, kinematics and dynamics of fluids. Fluid mechanics can also be divided into several categories, such as hydrodynamics, hydraulics, gas dynamics and aerodynamics.

1. Fluid statics: It deals with the behaviour of fluids at rest.
2. Fluid kinematics: It deals with motion of fluids without considering the forces causing flow.
3. Fluid dynamics: It deals with fluid flow subjected to forces.
4. Hydrodynamics: It deals with the motion of incompressible fluids, such as liquids (mainly water) and gases at low speeds.
5. Hydraulics: It deals with liquid flows, for example, flows in pipes and open channel.
6. Gas dynamics: It deals with the fluid flows that undergo significant density changes, for example, flows of gases through nozzles at high speeds.
7. Aerodynamics: It mainly deals with the flow of air over bodies, like automobiles, aircrafts, spacecrafts and rockets.