Chapter Five RAPIDLY VARIED FLOW (RVF)

1. Chapter Five RAPIDLY VARIED FLOW (RVF) 5.1 Characteristics of the Flow • Rapidly varied flow has very pronounced curvature of the streamlines. • The change in curvature may become so abrupt that the flow profile is virtually broken, resulting in a state of high turbulence ; this is rapidly varied flow of discontinuous profile, of which the hydraulic jump is an example. • In view of the contrast with-gradually varied flow, the following characteristic features of rapidly varied flow should be noted: 1.The Curvature of the flow is so pronounced that the pressure distribution cannot be assumed to be hydrostatic. 2. The rapid variation in flow regime often takes place in' a relatively short reach. Accordingly, the boundary friction, which would play primary role in a gradually varied flow, is comparatively small and in most. Cases insignificant. WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

2. 5.1 Characteristics of the Flow 3. When rapidly varied flow occurs in a sudden transition structure, the physical characteristics of the flow are basically fixed by the boundary geometry of the structure as well as by the state of the flow. 4. When rapid changes in water area occur in rapidly varied flow the The velocity distribution coefficient alpha and beta are usually far greater than unity and can not be accurately determined. WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

3. Cont… 5. Separation zones, eddies, and rollers that may occur in rapidly varied flow tend to complicate the flow pattern and to distort the actual velocity distribution in the stream. • In such cases, the flow is actually confined by one or more separation zones rather than solid boundaries. WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

4. 5.2 FLOW over spillways • Reading Assignment • Refer Open channel hydraulics books. • You will learn in dam eng.II WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

5. Hydraulic Jump • Hydraulic jump is one subject which has extensively been studied in the field of hydraulic engineering . • The Italian engineer Bidone (1818) first credited the first experimental investigation of this phenomena. • Since the n considerable research has undergone intio the study of this study. • The main reason for such continued interst in this topic is its immense utility in Hydraulic engineering and allied fields. WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

6. Hydraulic Jump • The theory of jump developed in early days is for horizontal or slightly inclined channels in which the weight of water in the jump has little effect upon the jump behavior and hence is ignored in the analysis. • The results thus obtained, however, applied to most channels encountered in engineering problems. • For channels large slope, the weight effect of water in the jump may become so pronounced that. it must be included in the analysis. WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

7. Practical applications • A hydraulic jump primarily serve as energy disssipator to dissipate the excess energy of flowing water down stream of hydraulic structures, such as spillways, and sluice gates. • Practical applications of the' hydraulic jump are many; some of the other uses are: 1.dissipate energy in water flowing over: dams, weir and other hydraulic structures mid thus prevent scouring of channels downstream from the structures. WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

8. Practical applications 2. to recover head or raise t he water level all the dovvn stream side of a measuring flume and thus maintain high water level in the channel for irrigation or other water-distribution purposes; 3. to increase weight on an a. pron and thus reduce uplift pressure under a masonry structure by raising the water depth on the apron; WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

9. Practical applications 4. to increase the· discharge' of a sluice by holding back tail water, since the effective head will be reduced if the tail water is allowed to drown the jump. 5. indicate special flow conditions, such as the existence of supercritical flow or the presence of a control section 0 that a gauging station may be located; 6. to mix chemicals used for water purification and so forth 7.to aerate water for city water supplies; and 8. to remove air pockets from water-supply lines and thus prevent air locking WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

10. Jump in horizontal rectangular channel • For supercritical flow in a horizontal rectangular channel, the energy of flow is dissipated through frictional resistance along the channel, resulting in a decrease in velocity and an increase in depth in the direction of flow. • A hydraulic jump will form in the channel if the -Froude number Fl of the flow, the flow depth YI; and a downstream depth y2 satisfy the equation WOU/KIOT, Department of WRIE Prepared by Gurmu D. Open channel Lecture Note

11. Interesting, right? This is just a sneak preview of the full presentation. We hope you like it! To see the rest of it, just click here to view it in full on PowerShow.com. Then, if you’d like, you can also log in to PowerShow.com to download the entire presentation for free.