Hydraulics Exam 2

Control point

Hydraulic structures and large changes in channel slop are sometimes called a ___________, where the flow characteristics change rapidly

Opening and closing valves, turning on pump

Hydraulic systems often experience sudden changes in flows when

Froude Number

A dimensionless number that represent the importance of the inertial forces to the field (gravity) forces in a flow field

Water hammer

Abrupt changes in dynamic closed conduit hydraulic systems create pressure waves that are known as

Compressibility of water and the pipe

Affects how quickly waves associated with water hammer are dissipated

Slows

As the compressibility of a fluid increases, the wave speed

Protect foundation lower water level

Bridge protection

Along the wetted perimeter

By what mechanism is energy dissipated in open channel flows

Intake of pump

Cavitation is likely to occur near the

Vapor pressure

Cavitation occurs when the absolute pressure in a hydraulic system drops below the _________________ of water

Trapezoids

Commonly employed in large-scale engineered channels

Along channel perimeter

Energy losses in open channel flow occurs

Static head

Energy needed to lift the water

Rivers, canals, sewer, treatment plants

Examples of open channel flow systems

Slope

Factors influencing open channel flow that can NOT be controlled is

Geometry and material

Factors influencing open channel flow that can be controlled are

Passes through critical depth

Flow measurement

Shape that has smallest perimeter for given area

For a given slope and material, what characteristics of the geometry will produce the biggest velocity

DeltaH(Qo + DeltaQ) ~ (2)(ki)(Qo)(DeltaQ) + (ki)(Qo^2)

Formula to approximate the headloss at Qo + DeltaQ based on a linear approximation of the function starting from a flow of Qo

Sub-critical

Fr < 1

Super-critical

Fr > 1

Dynamic head

Frictional losses that depend on flow rate

Geometry

In closed conduits, this is fixed In open channels, this varies in the direction of flow

Pressure

In closed conduits, this varies moving in the direction of flow. In open channels, this is fixed.

Maximum hydraulic radius

In rigid channels, the goal of the design is to maximize the velocity that is accomplished by

Downstream to upstream

In sub-critical flows, a disturbance in the flow goes from

Upstream to downstream

In super-critical flows, a disturbance in the flow goes from

Raise water level to ensure availablility

Irrigation

Runout

Maximum flow rate that can be delivered to a pump is its

Shut off head

Maximum head that can be supplied by a pump is known as the

Net positive suction head (NPSH)

Minimum head above the vapor pressure required to prevent cavitation within a given pump

Specific energy

Open channel flows are analyzed in terms of the

Gravity

Open channel flows are driven by

Turbulent, because big.

Open channel flows are primarily ___________. Why?

Centrifugal pumps

Operate at high pressures and low flows, most efficient kinds of pumps

Critical Depth

Over the top of the weir, the flow will pass through its

Head, power, and efficiency as a function of the flow rate

Pump curves typically depict

Energy

Pumps provide a mechanism to move water uphill by adding

Free board

Safety factor added to the minimum depth to ensure that the flow does not exceed the channel banks

Surge tanks

Structures that are open to the atmosphere that are placed near control points in hydraulic systems to reduce sudden changes in pressure due to valve closures

Bulk Modulus of Elasticity

The compressibility of a fluid is characterized by its

Critical depth

The depth associated with the minimum specific energy for a given discharge rate in a channel is known as

Normal depth

The depth associated with uniform, steady flows

Rated capacity

The flow rate corresponding to the point of highest efficiency is known as a pump's

Depth

The hydraulic radius of a very wide channel is best approximated by the

Surge tanks and closing the valve slowly

The two principal ways to mitigate the effects of water hammer:

Sound

The waves propagate through hydraulic systems at the speed of

Conservation of energy

Used to solve for flows in a network around loops

Conservation of mass

Used to solve for flows in a network at junctions

Fracture pipe walls and cause system failures

Water hammer can

Head (energy)

Water moves from a state of higher to lower

Axial flow pumps

Water on the suction side of the pump moves faster and experience lower pressures than on the discharge side, less efficient and provide less power

Flow, head average, capital cost of pump, operating costs for energy

What are major considerations that affect pump selection

Water temperature, elevation, height of pump above water, strainers

What are some factors that affect the propensity of cavitation for a hydraulic system

Semi-circle (complete)

What cross-section demonstrates flow with the greatest hydraulic efficiency

Normal depth

What do we get from Manning's equation

All energy losses are along the perimeter

What does it mean for the flow to vary "gradually"

Force gets big

What happens when velocity changes over a very short period of time

Pipe characteristics

When 1/Eb << Dk/Ep*e, the _________________ controls the wave speed

Fluid characteristics

When 1/Eb >> Dk/Ep*e, the _______________ controls the wave speed

Drawn down

When the flow transitions from sub-critical to super-critical this occurs

Hydraulic jump

When the flow transitions from super-critical to sub-critical this occurs

Flooding, erosion, structures

Why do engineers modify channel characteristics?

Energy losses inside the pump increase as flow/velocity increase

Why does the pump head curve slope downward