Effect of Flow Rate of Side-Type Orifice Intake on Withdrawn Water Temperature
Side-type orifice intake is a type of selective withdrawal facility used in managing reservoirs to mitigate the negative effects of low-temperature water. Based on the temperature data of a thermal stratified reservoir in China, an experiment was conducted in flume to study the influence of intake flow rate on withdrawn water temperature with different temperature distributions. Results indicated that withdrawn water temperature changed with different flow rates. The temperature change was determined by the water temperature gradients above and below the intake, whereas the change trend of temperature depended on the difference between the water temperature gradient above and below the intake. We likewise proposed a new equation with which the withdrawn water temperature of a thermal stratified reservoir using a side-type orifice could be calculated. These findings could be directly applied to the design and operation of side-type orifice intake in thermal stratified reservoirs.
Experimental and numerical study on the thrust of a water-retaining curtain
A water-retaining curtain (WRC) has become a useful facility in selective withdrawal and sedimentation control, but the force analysis of a curved curtain is still lacking. Based on flume experimental tests and numerical simulations, this paper analyzes the variation laws of pressure difference and thrust of WRC. The results show that under the uniform inflow condition, the distribution of pressure difference on the WRC is relatively even, and the maximum value is located at the upper part of the curtain. When arc length–height ratio increases, the location of maximum pressure difference gets lower. In addition, the variation law of thrust of WRC conforms to the classical resistance equation. The drag coefficient is found to fit a power function of the water-retaining ratio, a second-degree polynomial function of arc length–height ratio, and linear function of inclination ratio. The results also yield a simplified forecasting formula of thrust of WRC which is proposed and verified using flume simulations and a real reservoir model test. The newly developed formula systematically considers the water-retaining height, arc length and inclination degree, providing a rapid and accurate algorithm to predict the thrust, and lays a theoretical foundation for practical application.
On the sheared density interface of an entraining stratified fluid
This paper deals with the nature of the entrainment interface of a two-layer fluid subjected to interfacial velocity shear. The shear flow was generated by driving the mixed layer over the dense layer by a disk pump such that there is no stress at the top of the mixed layer. During the entrainment process a sharp, thin-density interfacial layer developed; its thickness δ was found to increase linearly with the mixed-layer depth h, independent of the Richardson number Riu. The shear layer thickness δs was found to be much larger than δ and the ratio δs/h is also found to be constant, irrespective of Riu. At the entrainment interface, the estimated buoyancy flux and the dissipation of turbulent kinetic-energy appear to be of the same order. This result supports an entrainment law of the form E ∼ Riu−1, where E is the entrainment coefficient. The interfacial layer showed sporadic large-amplitude wave oscillations whose amplitudes scaled well with the estimated size of the undulations caused by the impingement of large eddies (of size h) on the density interface. The density-interfacial layer was found to be ‘topped’ by a layer of partially mixed fluid which had not yet incroporated into the well-mixed region.