Effect of Flow Rate of Side-Type Orifice Intake on Withdrawn Water Temperature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stratified reservoir in China, an experiment was conducted in flume to study the influence of intake flow rate on withdrawn water temperature with different temperature distributions. Results indicated that withdrawn water temperature changed with different flow rates.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 We likewise proposed a new equation with which the withdrawn water temperature of a thermal stratified reservoir using a side-type orifice could be calculated.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.
Interfacial Mixing Caused by Turbulent Buoyant Jets
Laboratory experiments were carried out to investigate mixing and entrainment induced by a planar turbulent buoyant jet impinging on a stable density interface. The jet was released horizontally into the homogeneous bottom layer of a fluid system in which the top linearly stratified layer was separated from the homogeneous layer by a density discontinuity. This flow configuration has similarities to those that occur in solar ponds and ocean thermal energy conversion plants. The results reveal markedly different entrainment mechanisms, and thus entrainment laws, for different jet regimes that depend on the inlet buoyancy of the jet. Measurements included the entrainment velocity, interfacial‐layer thickness, and time evolution of vertical density profiles. Based on observations of entrainment mechanisms, simple theoretical models are developed to predict entrainment laws for slightly buoyant and neutrally buoyant jet regimes, and the model predictions are compared with the experimental results.
On mixing across an interface in stably stratified fluid
Mixed-layer deepening in stratified fluid has been studied experimentally in mean-shear-free turbulence generated by an oscillating grid. Conditions were varied over a wide range and both two-layered and constant-gradient fluid systems were considered. It is shown that the mixed-layer deepening rate is represented well by power laws, and when local scaling is used all the data can be collapsed on an entrainment relation E = K Ri−n with n = 1.50±0.05 when Ri [gsim ] 7. This power law suggests that the turbulent kinetic energy is made available for mixing on a buoyancy timescale characteristic of eddy recoil or internal-wave breaking rather than a turbulent-eddy overturning timescale. In the constant-gradient situation internal waves are generated which radiate energy away from the interface. An evaluation of the radiated energy indicates, however, that generally energy radiation does not affect the entrainment rate. The coefficient K therefore has the same value (K ≈ 3.8) in linearly stratified fluid as in the two-layer situation. The interface thickness is found to be a function of stability, but reaches an asymptotic value of h/D = 0.055 when Ri is very large. There is some indication that the interface thickness is also a weak function of Reynolds number.