SPATIAL HYDRAULIC JUMP IN GRADUAL AND SUDDEN EXPANSIONS

Abstract

Significance Of The Spatial Hydraulic Jumps 1.1.1 Hydraulic jump may be defined as a hydraulic phenomenon by means of which the flow passes in an abrupt manner from shooting to streaming condition causing a sudden discontinuity in the flow. This discontinuity is accompanied by vt lent impact and consists of an abrupt rise of water surface in the region of impact between the rapidly moving and slow moving streams. 1.1.2 Due to the rapid and abrupt change in the state of flow, there are energy losses. The greater and more abrupt the changes in the flow, greater will be the energy loss in the jump. A hydraulic jump is the most effective device for the dissipation of excessive energy below hydraulic structures, and it prevents the undesirable • effects of scouring down-stream, which would otherwise endanger the existence of these structures• The hydraulic Jump used for energy dissipation is usually confined to the stilling basin, constructed immediately down-stream of the hydraulic structure. The bottom of the stilling basin is constructed to resist scouring• 1.1.3 The energy dissipation within the Jump is a function of the conjugate depth at the end of the jump and the depth of flov before the jump. In practice in most cases the depth of flow available in the down-stream channel is much less than the conjugatb depth required for the jump to form within the stilling basins, and thus requiring excavation of the hard rocks resulting in excessive expenditure. In order to effect economy in the construction of the -stilling basins, it is essential that it should be laid' as high as possible. This can only be achieved through the increased energy dissipation within the jumpy since more the energy dissipation lesser the conjugate depth. 1.1.4 To achieve this -aim, the mechanics of the hydraulic jump and energy dissipation process should be well understood. During the formation of the hydraulic jump the kinetic energy of flow is conver• ted into turbulence and finally into heat energy, which can not be converted into potential or pressure energy back. Till recently energy dissipation was assumed to be inherent phenomenon in the flow itself and was considered that it could not be appreciably increased. 4 However the theories put forth by Kalinske and Hunter Rouse3 gave better insight into the mechanism of energy dissipation in the hydra.. ulic jump. In 1946 Kalinske4 in his experimental studies showed that the energy dissipation occurs mainly in the shear layers, which are the same as dividing layers or discontinuity layers between the main flow entering the expansion and the back flow on the side of the expansion. Rouse3 in 1958 colloborated Kalinske's findings. Rouse further says that the much of the energy dissipation within the jump occurs at the beginning of the jump itself in the shear layers lying between the top eddies and the main stream under-heath it....