Experiments were conducted to study the generation of air core and its effect on the outflow shape and discharge in a cylindrical water tank with a bottom well-designed outlet. Depending on the stages of the air core ...Experiments were conducted to study the generation of air core and its effect on the outflow shape and discharge in a cylindrical water tank with a bottom well-designed outlet. Depending on the stages of the air core in the tank, the outflow shape can vary from a smooth water jet to a smooth spindle shape with air-core, and to water sprays. The diameter of the nozzle size also has influence on the outflow pattern. The existence of the penetrated air core can dramatically reduce the outflow discharge, with the discharge coefficient decreasing with the nozzle diameter.展开更多
This paper reports that an experimental study is conducted to examine the dynamics of the outflow in two-layer exchange flows in a channel connecting between two water bodies with a small density difference. The exper...This paper reports that an experimental study is conducted to examine the dynamics of the outflow in two-layer exchange flows in a channel connecting between two water bodies with a small density difference. The experiments reveal the generation of Kelvin-Helmholtz (KH) instabilities within the hydraulically sub-critical flow region of the channel. During maximal exchange, those KH instabilities develops into large-amplitude KH waves as they escape the channel exit into the reservoir. The propagation speed of those waves, their generation frequency and their amplitudes are studied. The dynamics of the outflow and these waves are directly linked to the hydraulic conditions of the exchange flow within the channel.展开更多
Elevated levels of the total dissolved gas (TDG) may occur downstream the dams during the spill process to increase the incidence of the gas bubble disease for fish. With increasing numbers of cascade hydropower stati...Elevated levels of the total dissolved gas (TDG) may occur downstream the dams during the spill process to increase the incidence of the gas bubble disease for fish. With increasing numbers of cascade hydropower stations being constructed or planned, the cumulative effects of the TDG supersaturation become an increasingly prominent issue. Previous studies of the supersaturated TDG mainly focused on the generation process in the stilling basin downstream the dam while ignoring the saturation changes during the jet breakup process by assuming a 100% plunge-in-level. This assumption may lead to errors in the TDG generation predictions and the scientific assessments of the TDG supersaturation. Therefore, in this paper, physical experiments are conducted to analyze the dissipation of the supersaturated TDG in the jet breakup process, and to establish a quantitative relation between the initial TDG level and the detention time of the jet in the air. These results indicate how the supersaturated TDG generated by an upstream dam affects the TDG generation and provide a scientific support for accurate predictions of the supersaturated TDG generation for high dam spills.展开更多
文摘Experiments were conducted to study the generation of air core and its effect on the outflow shape and discharge in a cylindrical water tank with a bottom well-designed outlet. Depending on the stages of the air core in the tank, the outflow shape can vary from a smooth water jet to a smooth spindle shape with air-core, and to water sprays. The diameter of the nozzle size also has influence on the outflow pattern. The existence of the penetrated air core can dramatically reduce the outflow discharge, with the discharge coefficient decreasing with the nozzle diameter.
文摘This paper reports that an experimental study is conducted to examine the dynamics of the outflow in two-layer exchange flows in a channel connecting between two water bodies with a small density difference. The experiments reveal the generation of Kelvin-Helmholtz (KH) instabilities within the hydraulically sub-critical flow region of the channel. During maximal exchange, those KH instabilities develops into large-amplitude KH waves as they escape the channel exit into the reservoir. The propagation speed of those waves, their generation frequency and their amplitudes are studied. The dynamics of the outflow and these waves are directly linked to the hydraulic conditions of the exchange flow within the channel.
基金Project supported by the Fundamental Research Funds for the Central Universities(No.2009QNA4024)the Program for Zhejiang Leading Team of S&T Innovation(No.2010R50037),China
文摘Elevated levels of the total dissolved gas (TDG) may occur downstream the dams during the spill process to increase the incidence of the gas bubble disease for fish. With increasing numbers of cascade hydropower stations being constructed or planned, the cumulative effects of the TDG supersaturation become an increasingly prominent issue. Previous studies of the supersaturated TDG mainly focused on the generation process in the stilling basin downstream the dam while ignoring the saturation changes during the jet breakup process by assuming a 100% plunge-in-level. This assumption may lead to errors in the TDG generation predictions and the scientific assessments of the TDG supersaturation. Therefore, in this paper, physical experiments are conducted to analyze the dissipation of the supersaturated TDG in the jet breakup process, and to establish a quantitative relation between the initial TDG level and the detention time of the jet in the air. These results indicate how the supersaturated TDG generated by an upstream dam affects the TDG generation and provide a scientific support for accurate predictions of the supersaturated TDG generation for high dam spills.
