2017-10-20

Question 1

Explain the physical meaning of each term of the momentum equation and provide examples where each term is zero (or could be neglected)

Answer 1

Body forces: Fb
Surface forces: Fs

Steady flow → Body forces Fb = 0
Uniform flow → If the velocity across the inlet or outlet of the CV is uniform we could simply take it outside the integral.

Question 2

Starting from the Bernoulli equation in one point of a river cross section
(see white dot in the figure below), demonstrate that the total energy of water in that cross section can be written as:

Answer 2

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Question 3

a) In what circumstances(flow regimes)do you expect to have a hydraulic jump in a river?

b) Does the flow lose or gain energy during a hydraulic jump? Explain why.

c) draw the water depths upstream and downstream of hydraulic jump taking place between section 1 and 2.

d) Sketch on the figure the energy grade line from section A to section B

Answer 3

a) When the flow goes from supercritical to subcritical.

b) **There is an energy loss in the hydraulic jump. **When the flow goes from Supercritical Fr > 1 to Subcritical Fr < 1, the velocity decreases. The Specific energy is partially conserved by an increase in the depth of flow, however due to the turbulent nature of the hydraulic jump some frictional head loss occurs too. This friction means that kinetic energy from the system is lost due to heat produced during the hydraulic jump.

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