Hydraulic Energy Dissipators - A Review
Hydraulic Energy dissipators are devices to protect downstream areas of basin from erosion by reducing the velocity of flow up to an acceptable limit. The stilling basins are transition structures fabricated to dissipate excess energy confined by flow with high velocity at the outlet of conduit or tunnel so that the flow beyond the basin does not threaten the firmness of bed and banks of downstream channel in structures like culvert spillways, canal, etc. from scouring. Henceforth proper attention needed by hydraulic engineers for t he design of energy dissipators so as to obtain optimum energy dissipation at outlet. The type of stilling basin most suitable at a particular location mainly depends upon initial velocity of flow and initial Froude Number. This paper describe about the different type of energy dessipators with different appurtanances used in hydraulic structures for protection work.
EFFECT OF BAFFLE BLOCKS ON THE PERFORMANCE OF RADIAL HYDRAULIC JUMP
The effect of baffle block (sill) on a radial hydraulic jump (R.H.J.) has been investigated and analyzed, in order to derive the limiting design parameters for this type of jump in expanding channels. The limiting design conditions refer to the radial hydraulic jump, when it occurs entirely on the horizontal bed, with a sill liable to move in both horizontal and vertical directions. This study was carried out in the laboratory for Froude number ranged from 2 to 6.5 to find non-dimensional relationships between the design parameters of radial hydraulic jump for different height of local baffle blocks. Generally the obtained results showed a good fitting between the different' parameters. Also results indicated that the energy loss and the sequent depth for a radial hydraulic jump are affected by baffle blocks. INTRODUCTION Hydraulic jump is one of the classical problems in the field of applied hydraulics. It was first investigated experimentally by Bidonein in 1818. This led Belanger in 1828 to distinguish between mild (subcritical) and steep (supercritical) slopes. Hydraulic jump is frequently produced by barrier in originally uniform flow. There after abundant studies were made and the results were quoted by many Fourth International Water Technology Conference IWTC 99, Alexandria, Egypt 256 writers. Although most hydraulic jumps in stilling basins are rectangular in plan, there are several stilling basins that have diverging sidewalls. The term radial hydraulic jump refers to a jump in a stilling basin with diverging walls, i.e. radially expanding flow. The radial hydraulic jump can be controlled or affected by sills of various designs, such as sharp-crested weir, broad crested weir, and abrupt rise and drop in channel floor. The function of the sill is to ensure the formation of a jump and to control its position under all probable operating conditions. The energy loss in the radial hydraulic jump is slightly higher than the corresponding one in rectangular jump. In practice, the stilling basin is seldom designed to confine the entire length of a free hydraulic jump on the paved apron, because such a basin would be too expensive. Consequently, accessories to control the jump are usually installed in the basin. Baffles and sills are used simply as safety devices and the basin is designed to have the full, free jump sequent depth [7,8]. There are other designs for a reduced sequent depth in rectangular jump by assuming that appurtenances to dissipate a portion of the excess energy [1,6]. A few studies of diverging flow basins with baffle blocks have been reported in the literature. Moore and Meshgin in 1970 studied the use of the radial hydraulic Jump as an energy dissipator for culvert outlets, the Froude numbers in their experiments were relatively low (Fr < 3) while their flare angles were large (20<θ<60). Nettleton and McCorquodale [9] studied the effect of baffle blocks on the performance of the radial hydraulic jump. His results indicated that an end sill would improve the performance of the radial stilling basin. Therefore, in this study an attempt is made to explore design parameters for radial hydraulic jump on a horizontal slope with Fourth International Water Technology Conference IWTC 99, Alexandria, Egypt 257 affecting baffle blocks.
Force on Sill of Forced Jump
The mean force on a continuous sill in a forced hydraulic jump has been measured directly by a transducer for a wide range of experimental conditions. Four sills of heights expressed as multiples of the sluice opening are 1.0, 1.5, 2.0, and 3.0. The Froude number based on the flow at the sluice opening is varied from 3.99 to 9.09. The sills are situated at various distances from the sluice gate. The state of the flow is governed by the depth downstream of the sill. Maximum force is exerted when the supercritical stream impinges directly on the sill. The force reaches an asymptotic value at high submergence and it could be predicted for high sills using an elementary dynamic pressure model. The scale effect due to Froude number of the flow is discussed.