Ideal fluid
A fluid, which is incompressible and having no viscosity, is known as an ideal fluid. Ideal fluid is only an imaginary fluid as all the fluids, which exist, have some viscosity.
Real fluid
A fluid, which possesses viscosity, is known as real fluid. All the fluids, in actual practice, are real fluids.
Example: Water, Air etc.
Newtonian fluid
A real fluid, in which shear stress indirectly proportional to the rate of shear strain or velocity gradient, is known as a Newtonian fluid.
Example: Water, Benzine etc.
NonNewtonian fluid
A real fluid, in which shear stress is not directly proportional to the rate of shear strain or velocity gradient, is known as a NonNewtonian fluid.
Example : Plaster, Slurries, Pastes etc.
Ideal plastic fluid
A fluid, in which shear stress is more than the yield value and shear stress is proportional to the rate of shear strain or velocity gradient, is known as ideal plastic fluid.
Incompressible Fluid
A fluid, in which the density of fluid does not change which change in external force or pressure, is known as an incompressible fluid. All liquid are considered in this category.
Compressible fluid
A fluid, in which the density of fluid changes while a change in external force or pressure, is known as a compressible fluid. All gases are considered in this category.
Graphical representation of different fluids:
Tabular representation of fluid types:
Types of fluid

Density

Viscosity

Ideal fluid

Constant

Zero

Real fluid

Variable

Non zero

Newtonian fluid

Constant/ Variable

T = u(du/dy)

Non Newtonian fluid

Constant/ Variable

T ≠ u(du/dy)

Incompressible fluid

Constant

Non zero/zero

Compressible fluid

Variable

Non zero/zero

CLASSIFICATION OF FLOWS ON THE BASIS OF MACH NUMBER.
 Incompressible ﬂowM less than 0.3
 Compressible subsonic ﬂowM between 0.3 and 1
 Transonic flowM ranging from values less than 1 and more than 1
 Supersonic ﬂowM greater than 1 but less than 5
 Hypersonic ﬂow – M greater than 5