Rapidly Varied Flows Flashcards
How can Froude number be calculated?
Fr=U/√gh_m
What is the shallow water wave velocity?
The speed at which a small free-
surface disturbance propagates up- or down-stream in an open
channel flow
What does sub-critical flow encounter?
Sub-critical flow encounters increased slope or vice versa
What is controlled in sub-critical flow?
Downstream
What is the flow like in sub-critical conditions?
‘Tranquil’ or ‘slow’
What part of the channel is controlled in super-critical flow?
Upstream
What defines rapidly varied flows in fluid mechanics?
Rapid changes in depth and velocity over short distances, characterized by complex fluid phenomena
What is the significance of the Froude number in scale modelling of flows?
It represents the dynamics of the flow, ensuring lab models accurately capture those dynamics by matching the Froude number with the full-scale
How is the scale factor in fluid dynamics defined?
The ratio of characteristic length at full scale to the corresponding length in the model
What is the critical depth in open channel flow?
The depth at which the Froude number equals 1, distinguishing between sub-critical and super-critical flows
How does the flow change at critical depth?
Below critical depth, the flow is super-critical (faster); above it, the flow is sub-critical (slower)
What characterizes a hydraulic jump?
A rapid transition from super-critical to sub-critical flow, with sudden change in depth, air entrainment, and energy dissipation
What factors contribute to energy dissipation in a hydraulic jump?
Mixing, air entrainment, and the formation of a ‘roller’ contribute to energy loss
What are the typical efficiencies of energy dissipation in a hydraulic jump?
Between 15-55%
What purposes do control structures like sluice gates serve?
Controlling water depth, bed stabilization, and flood control
Under what assumption is Bernoulli’s equation applied to sluice gates?
Energy losses due to friction are negligible
How can you calculate the energy dissipated in the jump per unit time?
P_d=⍴g∆H_1Q
How does velocity scale?
√𝜆
How can scale factor be found?
𝜆=L_F/L_M
In a supercritical flow what is affected?
Downstream only
What are most river flows in England classified as?
Sub-critical
If h>h_c then flow is?
Subcritical
If h<h_c then flow is?
supercritical
If s>s_c the slope is?
Steep
