WK 6

Question 1

Define temporal variaitons

Answer 1

Variations with time

Question 2

When does steady flow occur?

Answer 2

when the various parameters at anypoint do not change with time.

Question 3

when does unsteady flow occur?

Answer 3

when the various parameters (e.g.the flow depth and velocity) at any point change with time. This makes unsteady flow far more complex – often too complex to solve analytically.

Question 4

label the diagram

Answer 4

Question 5

the 3 categories that unsteady falls into

Answer 5

1. the flow changes slowly e.g. the continuous filling or emptying of a reservoir.
2. the flow changes rapidly e.g. reciprocating machinery such as positive displacement pumps and in hydraulic and pneumatic servo-mechanisms.
3. the flow changes so quickly that elastic forces become significant e.g. sudden opening/closing of a valve.

Question 6

example of water hammer disaster

Answer 6

Steam Explosion, New York City 2007

Question 7

what is water hammer

Answer 7

independent phenomenon, which occur when pipe flow adjustments occur.

when abruptly reducing flow in pipe, pulses of pressure generated which travel back along the pipe.

Can damage pipe/control valve (pressure known as water hammer)

Question 8

how can you reduce water hammer effect?

Answer 8

• reduce velocity of liquid inside pipe by increasing pipe diameter
  (if flow rate is fixed- if not adjust flow rate)
• increase time over change in momentum occur (add flywheels to pumps, so spin slower/ close valve slowly)
• adjust speed of sound through fluid, increase flexibility by adding an anti-surge device.