Question

Which of the following is not an assumption for an ideal fluid flow for which Bernoulli's principle is valid:
A) Steady flow
B) Incompressible
C) Viscous
D) Irrotational

Answer 1

Hint: Bernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. This also means that the total mechanical energy of the moving fluid comprising the gravitational potential energy of elevation, the energy associated with the fluid pressure and the kinetic energy of the fluid motion, remains constant. The only property of liquid that is not involved in this definition is the property that causes a drag force.

Complete step by step answer:
Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. It is applicable in fluid mechanics. This theorem holds well for both compressible and incompressible flows. There are few assumptions which must be met for applying Bernoulli's equation. The flow must be steady. The flow must be incompressible which implies density must remain constant even pressure varies. The friction (viscosity) must be ignored. The significance of this principle is that the total pressure is constant along a streamline. So, we can assume that the flow is irrotational. So, these assumptions are valid for an ideal flow for which Bernoulli's equation is valid.

As we can see only vicious in options is missing in these assumptions, the correct option is option (C) i.e. Viscous.

Additional Information: The applications of Bernoulli's theorem can be seen in wings of aero planes, flying discs, ships, chimneys, etc.

Note: Bernoulli's principle is not valid in the boundary layer.
1. This principle mostly applies to non-viscous fluids.
2. Steady implies the flow parameters should remain constant at any point of time.