Question

What is the limit between a perfect fluid and a real fluid?

Answer 1

The limits between a perfect fluid and a real fluid.

1. Fluids are classified into two types: Ideal fluids and real fluids.
2. An ideal fluid is incompressible and has no friction during flow.
3. Throughout the flow, the juxtaposed fluid "layers" suffer only normal strains instead of tangential stresses.
4. Here as a result of the lack of friction among layers and consequently the lack of internal resistance to shearing action, a perfect fluid is inviscid. A boundary layer, which would be extremely near to a body immersed in a fluid flow, exhibits real fluid effects.
5. Ideal fluids are fluids that have no viscosity and are incompressible; they do not provide shear resistance.
6. Real fluids are fluids with viscosity. The shear resistance is always provided by these fluids.

Difference:

Characteristic	Ideal fluid	Real fluid
Compressible	No	Yes
Viscosity	No	Yes
Surface tension	No	Yes
Flow type	Laminar	Turbulent
Friction	No	Yes