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Hydraulics 2 > Channel flow > Flashcards

Channel flow Flashcards

1
Q

What is steady uniform flow

A

Occurs when gravity balances friction force

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2
Q

What are the conditions of steady uniform flow

A
  • Flow is steady
  • Bed slope is positive
  • Artificial channel with constant roughness
  • Channel is long, without any obstacle disturbances
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3
Q

What are two types of non-uniform open channel flow?

A

Rapid varied flow

Gradually varied flow

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4
Q

What is rapid varied flow?

A

Flow changes ins hort lengths of channel where friction can be ignored

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5
Q

What is gradually varied flow?

A

Flow changes in long lengths of channel where friction dominates

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6
Q

What is a flow control?

A

a device which creates a unique relationship between depth and discharge

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7
Q

What are the energy losses in open channel flow?

A
  • Friction losses, accumulate with distance

- local energy losses, due to sudden changes in channel cross-sections

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8
Q

over short reaches of a channel what is the total head?

A

Constant

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9
Q

What is plotted on a specific energy curve?

A

Specific energy (E) vs. depth (y) for a fixed discharge (Q)

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10
Q

What is critical flow?

A

The point of minimum specific energy and maximum discharge

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11
Q

What is critical velocity?

A

The velocity corresponding to the critical flow

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12
Q

On a specific energy diagram where does super-critical flow occur?

A

below the critical flow line

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13
Q

On a specific energy diagram where does sub-critical flow occur?

A

Above the critical flow line

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14
Q

What does the froude number define?

A

The regime of flow (FR=1; critical flow)

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15
Q

Is uniform flow condition a flow control

A

Yes it is

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16
Q

Will both total head and specific energy reduce along the channel, and why?

A

Specific energy is part of total head, which reflects flow characteristics.
The difference between them is , the level of channel bed
-The total head would reduce, due to friction, but specific energy is related to the channel bed so could go up down or stay the same….

17
Q

Equation for critical water depth (yc) when we have a constant q?

A

yc=(q^2/g)^(1/3)

18
Q

Equation for critical water flow (yc) when we have a constant E (total head)

A

yc=2/3 E

19
Q

Equation for critical velocity

A

Vc=(gyc)^0.5

20
Q

What is E

A

Specific energy

21
Q

What’s the equation to get the depth corresponding to critical flow for non-rectangular channels?

A

Q^2/g=A^3/B where B is the top width of the channel and this is because dA/dy=approx. B

22
Q

What’s the equation for the Froude Number?

A

Fr=V/SQRT(gy)

23
Q

What does a flow control do

A

Defines the depth at which water will flow in an open channel; often transitions a flow from subcritical to supercritical

24
Q

What are some examples of engineered flow controls:

A
  • Sluice Gates
  • Weirs
  • Flumes….
25
Q

What occurs during flow under a sluice gate

A

No energy loss, depths remain same

26
Q

What occurs during flow over a weir?

A

There is a change in height (Z)

27
Q

What occurs in a Venturi Flume constriction

A

It is designed to produce critical; depth, so flow measurements can be taken

28
Q

What’s the area of a trapezoidal cross section?

A

(b+my)y

29
Q

What is the most economic cross-section

A

The cross section that will give maximum discharge for a given area.

30
Q

How can the most economic cross section be calcualted?

A

For a given A and S, Q will be maximum for a maximum Rh
Rh=A/P so max Rh means having a minimum P
Use dp/dy=0 to find these values

31
Q

What are non-erodible channels?

A

A technique of minimising lining material costs by creating teh most economic cross-section

32
Q

What are erodible channels?

A

based on the principles of maximum permissible velocity, creating a stable hydraulic section.

33
Q

What is Manning’s equation (velocity)

A

V=1/n Rh ^2/3 S^1/2

Hydraulics 2 (1 decks)

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