Fundamentals of Fluid Flow

Fluid Flow

movement of fluid through a system under the influence of external forces such as gravity, friction, and pressure.

Discharge

Also known as “Flow Rate”, amount of fluid passing through a section per unit of time

Laminar Flow

Based on Flow Pattern, when the path of the individual fluid particles do not cross or intersect. These flow is smooth and orderly and particles move in parallel layers.

Turbulent Flow

Based on Flow Pattern, when the path of the individual particles are irregular and continuously cross each other. The flow is chaotic with irregular fluctuations in velocity and pressure.

Reynolds Number

a dimensionless quantity used to determine the type of fluid flow, whether it is laminar, transitional, or turbulent.

It represents the ratio of inertial forces to viscous forces in a flowing fluid.

Steady Flow

Based on Time Variation, constant with time

Unsteady Flow

Based on Time Variation, varies with time

Compressible Flow

Based on Compressibility, typically occurs with gasses. Changes significantly with pressure and temperature.

Incompressible Flow

Based on Compressibility, typically occurs with liquids. Remains nearly constant, regardless of pressure and temperature changes.

One-Dimensional Flow

Based on Dimension Variation, occurs when direction and magnitude of the velocity at all points are identical.

Two-Dimensional Flow

Based on Dimension Variation, occurs when the fluid particles move in plane or parallel planes and the streamline patterns are identical in each plane.

Three-Dimensional Flow

Based on Dimension Variation, occurs when fluid properties vary in all directions.

Uniform Flow

Based on Uniformity of Flow, average velocity is constant across all sections. Occurs when an incompressible fluid flows through a stream with uniform cross-section.

Non-Uniform Flow

Based on Uniformity of Flow, occurs when the stream changes in velocity and cross-sections

Continuous Flow

Occurs when at any time, the discharge at every section of the stream is the same.

Streamlines

Imaginary curves drawn through a fluid to indicate the direction of motion in various sections of the flow of the fluid system

Streamtubes

Represents elementary portions of a flowing fluid bounded by a group of streamlines which confine the flow

Flow nets

Drawn to indicate flow patterns in case of two-dimensional flow, or even three-dimensional flow

Head

amount of energy per pound or Newton of fluid

Energy

It is the ability to do work

Kinetic Energy

Ability of a mass to do work by virtue of its velocity

Elevation Energy

the energy possessed by a fluid due to its elevation above a chosen datum.

Pressure Energy

energy possessed by the fluid due to its pressure

Total Flow Energy

total energy or head in a fluid flow is the sum of the kinetic and potential energies.

Power

the rate at which work is done

Efficiency

ratio of useful output energy to input energy. It is usually expressed in percentage.

Bernoulli’s Energy Theorem

total energy in a steadily flowing fluid system is constant along the flow path.

Bernoulli’s Principle

the speed of a moving fluid increases, the pressure within that fluid decreases.

Head Loss

reduction in head or pressure. It is a measure of the energy loss in a fluid system.

Hydraulic Grade Line

Also known as Pressure Gradient, Graphical Representation of the potential head. It is the line to which liquid rises in successive tubes.

HGL

• slopes downward in the direction of flow but it may rise or fall due to the change in velocity or pressure

• HGL is parallel to EGL for uniform pipe cross-section

Energy Grade Line

Always above the Hydraulic Grade Line by an equal amount of velocity head. It is the representation of the total energy of flow

EGL

• slopes downward in the direction of flow and will only rise with the presence of pump.

• EGL is parallel to HGL for uniform pipe cross-section