Fluids can be classified into the following types:
- Ideal fluid
- Real fluid
- Newtonian fluid
- Non-Newtonian fluid
- Ideal plastic fluid.
Ideal Fluid: A fluid which is incompressible and has no viscosity falls in the category of an ideal fluid. Ideal fluid is not found in reality so it is termed as an imaginary fluid since all the fluids that exist in the environment have some viscosity. There is no ideal fluid in reality.
Real Fluid: A fluid which possesses at least some viscosity is termed as real fluid. Actually, all the fluids existing or present in the environment are called real fluids. Some of its examples are petrol, air etc.
Newtonian Fluid: If a real fluid obeys the Newton’s law of viscosity i.e. the shear stress is directly proportional to the shear strain or velocity gradient then it is known as a Newtonian fluid. Some of its examples are water, air, alcohol, glycerol, thin motor oil etc.
Non-Newtonian Fluid: If the real fluid does not obey Newton’s law of viscosity i.e. if the shear stress is not proportional to the shear strain or velocity gradient then it is called Non-Newtonian fluid. Some of its examples blood, saliva, Soap solutions, cosmetics, and toothpaste etc.
Ideal Plastic Fluid: A fluid having the value of shear stress more than the yield value and shear stress is proportional to the rate of shear strain (velocity gradient) is known as ideal plastic fluid.