Papers by Keyword: Stilling Basin

Abstract: In stilling basins there is a change in flow regime from supercritical to subcritical flow; this transition is called a hydraulic jump. To control and stabilize the position of the jump, it is necessary to place a sill across the flow. A bibliographical analysis showed that when the controlled hydraulic jump is entirely formed upstream of the stilling basin, the sill has no effect on the configuration of the jump. However, when the jump length stretches beyond the sill position, this results in jump compactness and leads to several configurations of the latter, until it completely disappears. The main objective of this study is to determine the effect of the hydraulic jump compactness on the main jump features in a trapezoidal horizontal channel. Dimensionless empirical relationships depending on the jump compactness are obtained. Through this study, we aim to show the advantages of the jump compactness on the channel dimension. Indeed, the hydraulic jump is led to its most reduced form, before disappearing, in terms of tail water depth and jump length. Thus, the obtained results are useful for dimensioning the stilling basin.

Abstract: 3D numerical simulation is carried out for the water flow in stilling basin with X shaped flaring gate pier when the radial gate uses four different opening velocities. The space-time change law of hydraulic characteristics is obtained. The water level in the stilling basin is relatively higher while using lower opening velocities during the processes. The negative pressure exists on weir surface while the relative opening degree is less than 0.55; the maximal pressure on the slab of ogee section and stilling basin increases and moves to downstream with the gate opening. The results can provide important basis for shape optimization of practical engineering.

Abstract: 3-D numerical simulation is carried out for the water flow when the three overflow radial gates use different opening velocities. The space-time change law of hydraulic characteristics is obtained. The water surface profile in the stilling basin fluctuates greatly during the processes; the maximum pressure on the slab of stilling basin increases and moves to downstream with the gates opening; the velocity near the slab of stilling basin corresponding to the left orifice is much larger than that corresponding to the right one. The calculated water surface profile is in good agreement with the results obtained in experiments. The results can provide important basis for operation mode of radial gate.

Abstract: Based on hydraulic and acoustic theory, a model test of broad-crested weir was carried out, and the fluctuating pressure and corresponding noise values of stilling pool base slab were measured and recorded with three schemes of different flow rates. The results showed that the fluctuating pressure and noise value of water flow increased with the increasing of flow rate, the fluctuating pressure have certain correlation with the noise value, where the largest fluctuating pressure appeared had the same section with the noise value, yet the fluctuating pressure change trend was not identical to the noise value. The main reasons of producing flow noise were the interaction of flow and solid bottom and the flow turbulence.

Abstract: The principle of energy dissipation in stilling basin is based on hydraulic jump formation. Due to the inherent fluctuating characteristic of the hydraulic jump, basin floor is subjected to variations of pressure, resulting in unstableness due to uplift forces. To increase the efficiency of the stilling basins and improve the energy dissipation rate, one or two rows of baffle blocks are applied on the basin floor. Causing a forced hydraulic jump, tension and compression forces are exerted by pressure fluctuations of rotating roller zone of hydraulic jump. In this investigation, to observe the impacts of baffle blocks on pressure fluctuations on basin floor, a standard USBR basin model type III was constructed, and then a second row of blocks was added to the basin. A set of pressure tubes was fixed along the axis of the basin to measure the static and dynamic pressures on basin floor. The results were expressed in dimensionless parameters including C-p, C+p, C’p, Cp. Also, power spectra of pressure fluctuations were calculated. The results show a decreasing trend in root mean square of pressure fluctuations as distancing from toe of jump along the basin with and without baffle blocks. Also, mean pressure increases when water jet strokes the basin then decreases under roller zone of jump and increases again after sequent depth. The spectral analysis indicates that the dominant frequency is between 10 rad/s and 35 rad/s and pressure fluctuations have low frequency characteristics.

Abstract: To protect downstream of hydraulic structures against erosion and degradation, must dipress water energy. one of the most comon methods to achive this purpose is constructing the stilling basin at the downstream of such structures. In stilling basin, the water energy dissipated by taking place of hydraulic jump. When a hydraulic jump occurs, the hydrodynamic and hydrostatic forces effect on the stilling basin floor slab. These forces include the force due to water weight and the up lift force affected the slab below which these forces are classified in hydrostatic. also the other force is hydrodynamic force due to pressure fluctions below the hydraulic jump. To keep the stilling basin stabillity from liffting up and destruction must the resistant forces be equal to destroyer forces. In this study after discution about the hydraulic jump and its resultant forces, a equation has been offerd to determine the thickness of stilling basin floor slab using buckingham theory andsoftware DATAFIT. Finaly the slab which evaluated by physical model, simulated using mathematical model(software ANSYS 10) and studied. The stress and strain diagrams were extracted. Results showed that physical and mathematical models were matched very good.

Abstract: Abrupt changes of the channel bed elevation in hydraulic systems, e.g. in chutes, drops and steeped spillways, results to create a sever flow kinematic energy. This excess energy, can tend to different phenomena, such as tremendous forces, scouring and degrading the channel bed, resulting to destruction of the downstream hydraulic structures. The most important source to cause this phenomena is the the existence of sequent vertical drops along the the channel. In this study, the energy dissipation efficiency was increased by installing a new type of dissipaters namely netting dissipater on the crest of the vertical drops based on model experimtation. Also, the features of hydraulic jump, created in the stilling basin, were compared to those of a simple vertical drop. By assembling the above mentioned structure to the top of the stilling basin, the jet flow direction is changed, the degree of turbulence is increased and as the results, the kinematic energy loss increases and the length of the hydraulic jump decreses. The enhanced efficiency of the proposed structure was quantified based on the achieved experimental data.