Hydraulics and Hydrology

System

A quantity of matter or region in space specified for analysis

Boundary

The real or imaginary surface that separates the system from its surroundings: can be fixed or movable

Closed System

A fixed amount of mass; no mass can cross its boundary

Open System

A properly selected region in space; flow crosses the boundary; also called a control volume

Property

Characteristics of a system

List the properties

Pressure, Temperature, volume, and mass

Intensive property

Intendent of system mass

Extensive property

Dependent on mass of system

Specific property

Extensive property per unit mass or volume

Density

mass of substance/ volume of substance

Specific weight

weight of substance / volume of substance

Specific gravity

density of substance/ density of water at 4 degrees Celsius

Viscosity

property that represents the internal resistance of a fluid to motion, or its fluidity

Dynamic viscosity

the proportionality constant between the shear stress and the strain rate

No-slip condition

fluid in motion comes to a complete stop at the surface and assumes a zero velocity relative to the surface: the direct contact with a solid “sticks” to the surface, and there is no slip

Pressure

Normal force exerted by a fluid per unit area; the same in all directions at any point in a fluid; has magnitude but no specified direction, and is therefore a scalar quantity

Absolute Pressure

actual pressure at a given point relative to absolute vaccum (absolute zero)

Gauge Pressure

pressure relative to atmospheric pressure

Atmospheric pressure

barometric pressure within the atmosphere of Earth

Hydrostatic

due only to the weight of the fluid; for an incompressible fluid, varies linearly with depth

Hydrostatic Force

hydrostatic pressure at the centroid of the surface upon which it is acting, multiplied by the area of the surface

Viscous flow

Flow in which frictional effects are significant

Inviscid flow region

regions of flow in which viscous forces are negligibly small compared to inertial or pressure forces

Internal Fluid

Fluid is completely bounded by solid surfaces; dominated by the influence of viscosity throughout the flow field; flow in a pipe or duct that is flowing full

External Flow

Flow of unbounded fluid over a surface; viscous effects are limited to boundary layers near solid surfaces and wake regions downstream of bodies

Incompressible Flow

Density of fluid remains constant or nearly throughout (the volume of every portion of fluid remains unchanged over the course of its motion); liquid flow

Compressible Flow

Density of fluid changes between portions of fluid; some gaseous flows

Steady Flow

No change in fluid properties at a point with time

Unsteady Flow

Change in fluid properties at a point with time

Uniform flow

No change in fluid properties with location over a specified region

Turbulence

Fluid flow is streamlined at low velocities and becomes chaotic as the velocity is increased above a critical value

Turbulent Flow

velocity fluctuations and highly disordered motion

Transitional Flow

flow fluctuates between laminar and turbulent flows

Laminar Flow

smooth streamlines and highly ordered motion

Streamline

A curve that is everywhere tangent to the instantaneous local velocity vector

Static Pressure

does not incorporate any dynamic effects; represents the actual thermodynamic pressure of the fluid

Dynamic Pressure

represents the pressure rise when the fluid in motion is brought to a stop

Hydrostatic Pressure

accounts for the elevation effects, i.e fluid weight on pressure

Internal Flow (closed-conduit flow)

fluid is completely bounded by solid surfaces; dominated by the influence of viscosity throughout the flow field; flow in a pipe or duct that is flowing full