Fluid Mechanics Quiz

Fluid mechanics is the study of the behavior of fluids at rest (fluid statics) or in motion (fluid dynamics), and the interaction of fluids with solids or other fluids at the boundaries.
Mechanics is the oldest physical science that studies both stationary and moving bodies under the influence of forces.
Statics is the branch dealing with bodies at rest.
Dynamics is the branch dealing with bodies in motion.

A substance that exists as a liquid or a gas is referred to as a fluid.
A solid can resist shear stress by deforming, whereas a fluid deforms continuously under the influence of shear stress, no matter how small.
In solids, stress is proportional to strain; in fluids, stress is proportional to strain rate.
In a liquid, molecules can move relative to each other, but the volume remains constant due to strong cohesive forces between the molecules.
A gas takes the shape of the container it is in, and it does not form a free surface in a larger container in a gravitational field because the cohesive forces are very small and the gas molecules are widely spaced.

Viscous versus Inviscid Regions of Flow:
- Fluids involve viscous effects to some degree.
- Viscous flows are flows in which the frictional effects are significant.
- Inviscid flow regions (typically regions not close to solid surfaces) allow viscous forces to be negligible compared to inertial or pressure forces.
Internal versus External Flow:
- Internal flow is when the fluid is completely bounded by solid surfaces (e.g., flow in a pipe or duct).
- External flow is when the fluid is unbounded and flows over a surface (e.g., airflow over a car).
Compressible versus Incompressible Flow:
- Incompressible flow assumes the density remains nearly the same throughout the flow.
- Compressible flow accounts for density changes during flow.
Laminar versus Turbulent Flow:
- Laminar flow is highly ordered and characterized by smooth layers of fluid.
- Turbulent flow is highly disordered and characterized by velocity fluctuations.
Natural versus Forced Flow:
- Natural flow is caused by natural means like buoyancy, where warmer lighter fluid rises and cooler denser fluid falls.
- Forced flow is caused by external forces like a pump or a fan.
Steady versus Unsteady Flow:
- Steady flow implies no change at a point with time.
- Unsteady flow implies change at a point with time.
- Uniform flow implies no change with location over a specified region.

Density (p): Mass per unit volume, usually constant for liquids, variable for gases.
Specific weight (w): Weight per unit volume.
Specific Volume: The volume occupied per unit of mass.
Specific Gravity (S): Ratio of the weight density or density of a fluid to the weight density or density of a standard fluid (e.g., water or air)

Viscosity is the property of a fluid that offers resistance to the movement of one layer of fluid over another adjacent layer.
Viscosity is caused by cohesive forces between molecules in liquids and by molecular collisions in gases.
Viscosity of liquids decrease with increasing temperature.
Viscosity of gases increases with increasing temperature.

Ideal Fluid: Incompressible and has no viscosity - A theoretical concept, not found in reality
Real Fluid: Possesses viscosity
- All the fluids in actual practice are real fluids
Newtonian Fluid: Shear stress is directly proportional to the rate of shear strain.
Non-Newtonian Fluid: Shear stress is not proportional to the rate of shear strain. - Examples: blood, paints, and some polymers.

Using control volume for the overall features of a flow (e.g., mass flow rate, net forces)
Using differential analysis to obtain details about the flow at every point in the flow field.

Streamline: line everywhere tangent to the velocity vector (instantaneous)
Pathline: actual path traversed by a given fluid particle
Streakline: locus of particles that have passed through a prescribed point (time dependent)
Timeline: set of fluid particles that form a line at a given instant in time (time dependent)

Variables, including velocity, pressure and temperature are quantified by units.

Gases undergo large variations in density with changes in pressure and temperature.
The relationship between pressure, specific volume, and temperature is given by the equation of state.

Surface tension is the tensile force acting on the liquid surface, similar to a membrane.
Surface tension results from unbalanced cohesive forces of the liquid molecules at the surface.
Capillarity refers to the rise or fall of a liquid surface in a small tube held vertically in the liquid due to the attraction (adhesion) between the wall of the tube and liquid molecules.

Dimensional analysis is crucial in simulating real-world scenarios.
Nondimensional parameters aid in testing and analysis of fluid phenomena.
Geometric similarity, kinematic similarity, and dynamic similarity are essential to successful model testing.

The Bernoulli equation is a statement of the conservation of mechanical energy.
It expresses the relationship between pressure, elevation and velocity in a flowing fluid, subject to certain assumptions.
Includes stagnation tubes, pitot tubes, orifices, and venturi to calculate fluid flow.