More Related Content
Similar to Rapidly variying flow (20)
![BBC NW_Tech Facilities_30 Odd Yrs Ago [J].pdf](https://cdn.slidesharecdn.com/ss_thumbnails/bbcnwtechfacilities30oddyrsagoj-250830230619-0d747bd6-thumbnail.jpg?width=560&fit=bounds)
Rapidly variying flow
- 1. Babaria Institute Of Technology, Vadodara. Applied Fluid Mechenics. A Presentation on ‘Rapidly Variying Flow’ By:- Milan Sheta(130050106109) Vikram Sindhav(130050106111)
- 2. Introduction • Rapidly-varied flow is a significant change in water depth over a short distance (a few times water depth). • It occurs where there is a local disturbance to the balance between gravity and friction (e.g. at a weir, venturi, sluice, free overfall, sudden change in slope, ...) or a mismatch between the depths imposed by upstream and downstream conditions (hydraulic jump).
- 3. • Often there is a critical flow transition between deep, slow flow (subcritical; Fr < 1) and shallow, fast flow (supercritical; Fr > 1). • The assumption that the flow varies rapidly over a relatively short distance means that bed friction is unimportant. Thus, for a smooth transition (e.g. weir, venturi or sluice), the total head is usually assumed constant through this short region.
- 4. • For an abrupt transition (hydraulic jump) there may be significant head loss, but it is associated with high levels of turbulence, not bed friction. • Note that the hydrostatic pressure assumption can only be applied where near-parallel flow has been re-established, either side of the rapidly-varying-flow region.
- 5. Hydraulic Jump • A hydraulic jump is an abrupt change from a shallow, high-speed flow to a deep, low-speed flow of lower energy. • It occurs when a depth difference is imposed by upstream and downstream conditions. Rapid, shallow flow may be created by, for example, a steep spillway or sluice. • A slower and deeper downstream flow may be controlled by a downstream weir or by a reduction in slope.
- 6. • The triggering of a hydraulic jump at the base of a spillway is desirable to remove surplus kinetic energy in order to reduce downstream erosion. V1 h2 h1 V2
- 9. Across a hydraulic jump • Mass is conserved. • The momentum principle is satisfied. • Mechanical energy is lost (mostly as heat).
- 10. Assume, for simplicity • Small slope (downslope component of weight of can be neglected). • Wide or rectangular cross-section. • Velocity uniform over upstream and downstream cross-sections.
- 11. • The length of the jump is short (so that bed friction can be neglected).
- 12. Thank You