In this paper,the dynamic characteristics of a vertical vortex are examined by the theoretical method and the particle image velocimetry(PIV)technology.The results of the theoretical analysis validate that the main pa...In this paper,the dynamic characteristics of a vertical vortex are examined by the theoretical method and the particle image velocimetry(PIV)technology.The results of the theoretical analysis validate that the main parameters of the vertical vortex are the Reynolds number Re,water level WL^(*)and velocity circulationΓ_(N).The experimental results indicate that,for the same Re,the low water levels are responsible for an intensive vortex intensity(maximum vorticity),but for a high-water level,water level is no longer a significant influencing factor on vortex intensity.TheΓ_(N)number increases with the rising of the Reynolds number Re and drops with the height of measurement section enhance for a low water level case.For the higher WL^(*),Γ_(N)does not decrease significantly.The formation and evolution of the vertical vortex in the present paper can be utilized or restrained by controlling the relevant dynamic parameters.Obtained research results may provide an important reference for engineering applications with possible occurrence of vertical vortex phenomenon.展开更多
The trace of vertical vortex flow at hydraulic intakes is of the shape of spiral lines, which was observed in the presented experiments with the tracer technique. It represents the fluid particles flow spirally from t...The trace of vertical vortex flow at hydraulic intakes is of the shape of spiral lines, which was observed in the presented experiments with the tracer technique. It represents the fluid particles flow spirally from the water surface to the underwater and rotate around the vortex-axis multi-cycle. This process is similar to the movement of screw. To describe the multi-circle spiral characteristics under the axisymmetric condition, the vertical vortex would change not only in the radial direction but also in the axial direction. The improved formulae for three velocity components for the vertical vortex flow were deduced by using the method of separation of variables in this article. In the improved formulae, the velocity components are the functions of the radial and axial coordinates, so the multi-circle spiral flow of vertical vortex could be simulated. The calculated and measured results for the vertical vortex flow were compared and the causes of errors were analyzed.展开更多
The air-trapped vertical vortices（ATVVs） are easy to form above the throttled orifices in the widely used long-corridor-shaped surge tanks（LCSSTs）, when the tank water level decreases rapidly during hydraulic tran...The air-trapped vertical vortices（ATVVs） are easy to form above the throttled orifices in the widely used long-corridor-shaped surge tanks（LCSSTs）, when the tank water level decreases rapidly during hydraulic transients. These ATVVs may jeopardize the operation safety of the hydropower stations and should be avoided. This study elucidates the formation mechanism of the ATVVs and proposes some simple measures to eliminate them. The 3-D CFD model for predicting the ATVVs is validated first by physical model tests in a model tailrace LCSST, and then the formation mechanism is analyzed based on the numerical results. It is shown that the main influence factor for the ATVVs is the critical submergence, which can be reduced by minimizing the velocity circulation around the throttled orifices. Two practical ATVV elimination measures through suppressing the velocity circulation are compared and verified, and the optimized one is recommended.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52279084)the Fundamental Research Funds for the Central Universities(Grant No.2024JC003).
文摘In this paper,the dynamic characteristics of a vertical vortex are examined by the theoretical method and the particle image velocimetry(PIV)technology.The results of the theoretical analysis validate that the main parameters of the vertical vortex are the Reynolds number Re,water level WL^(*)and velocity circulationΓ_(N).The experimental results indicate that,for the same Re,the low water levels are responsible for an intensive vortex intensity(maximum vorticity),but for a high-water level,water level is no longer a significant influencing factor on vortex intensity.TheΓ_(N)number increases with the rising of the Reynolds number Re and drops with the height of measurement section enhance for a low water level case.For the higher WL^(*),Γ_(N)does not decrease significantly.The formation and evolution of the vertical vortex in the present paper can be utilized or restrained by controlling the relevant dynamic parameters.Obtained research results may provide an important reference for engineering applications with possible occurrence of vertical vortex phenomenon.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50379030)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20020610016).
文摘The trace of vertical vortex flow at hydraulic intakes is of the shape of spiral lines, which was observed in the presented experiments with the tracer technique. It represents the fluid particles flow spirally from the water surface to the underwater and rotate around the vortex-axis multi-cycle. This process is similar to the movement of screw. To describe the multi-circle spiral characteristics under the axisymmetric condition, the vertical vortex would change not only in the radial direction but also in the axial direction. The improved formulae for three velocity components for the vertical vortex flow were deduced by using the method of separation of variables in this article. In the improved formulae, the velocity components are the functions of the radial and axial coordinates, so the multi-circle spiral flow of vertical vortex could be simulated. The calculated and measured results for the vertical vortex flow were compared and the causes of errors were analyzed.
基金Project supported by the National Natural Science Foundation of China(Grant No.51579187)
文摘The air-trapped vertical vortices（ATVVs） are easy to form above the throttled orifices in the widely used long-corridor-shaped surge tanks（LCSSTs）, when the tank water level decreases rapidly during hydraulic transients. These ATVVs may jeopardize the operation safety of the hydropower stations and should be avoided. This study elucidates the formation mechanism of the ATVVs and proposes some simple measures to eliminate them. The 3-D CFD model for predicting the ATVVs is validated first by physical model tests in a model tailrace LCSST, and then the formation mechanism is analyzed based on the numerical results. It is shown that the main influence factor for the ATVVs is the critical submergence, which can be reduced by minimizing the velocity circulation around the throttled orifices. Two practical ATVV elimination measures through suppressing the velocity circulation are compared and verified, and the optimized one is recommended.
