A fluid is said to be ideal inviscous and incompressible. Ideal fluid An ideal fluid is a fluid that has several properties including the fact that it is: • Incompressible – the density is constant • Irrotational – the flow is smooth, no turbulence • Nonviscous – (Inviscid) fluid has no internal friction ( η = 0) Ideal fluid do not actually exist in nature, but sometimes used for fluid flow problems.