Flip buckets are commonly used to discharge flow away from a hydraulic structure into the downstream to dissipate energy.A new leak-floor flip bucket is presented,making the ski-jump water jet a typical long-narrow na...Flip buckets are commonly used to discharge flow away from a hydraulic structure into the downstream to dissipate energy.A new leak-floor flip bucket is presented,making the ski-jump water jet a typical long-narrow nappe.Based on the model experiments and numerical simulation,the flow pattern,formation process and mechanism of the leak-floor flip bucket are studied.The results show that cross section flow shape develops from the"Y-type"to"|-type",and this is because the natural pressure difference is generated when water flows through the leak-floor area and moves transversely from both sides to the center.Different from the slit-type flip bucket with sidewall contraction,the leak-floor flit bucket makes the water jet narrow and long without high pressure on the side walls of the flip bucket.Under the same jet length condition,the maximum sidewall pressure of the slit-type is 4.67 times that of the leak-floor flip bucket.The effects of flow discharge on the jet length are less significant for the leak-floor bucket than for the slit-type bucket.展开更多
Bubble collecting, bubble holding and micro-bubble ejecting characteristics of pit structure and the influence of cavitation bubble on the development of erosion pit are investigated by means of highspeed photography ...Bubble collecting, bubble holding and micro-bubble ejecting characteristics of pit structure and the influence of cavitation bubble on the development of erosion pit are investigated by means of highspeed photography experiments. Pits tend to collect and hold wandering cavitation bubbles. The air holding phenomenon of pits can be a destination of the incubation period in the process of cavitation erosion. The holding bubble tends to eject micro-bubbles from the top of holding cavitation bubble, making the pit a source of nuclei. With bubbles being held in pits, the diameters of pits increase rapidly. But in the given experiment condition, there is a specific stable value beyond which the diameter of pits will not increase. This characteristic will be helpful in understanding and predicting the cavitation erosion process.展开更多
In hydraulic engineering,free-surface aeration is a natural phenomenon occurring in smooth channel flows.In self-aerated flows,a key aspect that has not yet been well understood is the formation mechanism of free-surf...In hydraulic engineering,free-surface aeration is a natural phenomenon occurring in smooth channel flows.In self-aerated flows,a key aspect that has not yet been well understood is the formation mechanism of free-surface air entrainment.In this research,the process of free-surface entrapped deformation is analyzed theoretically and the critical radius of curvature for air entrainment is obtained,affected by flow mean velocity and depth.When the severity of local free-surface deformation exceeds the critical condition,the entrapped free surface encounters closure in the unstable deformation movement process,resulting in air entrainment.This inference agrees well with observed experimental results that are obtained from the processes of surface entrapped deformation and air entrainment captured by a high-speed camera-based data acquisition system.This agreement indicates that self-aeration occurs in low-velocity open-channel flows.It is also confirmed that free-surface turbulent deformation provides a mechanism for air entrainment.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51379138&51179113)Sichuan Province Funds for Distinguished Young Scientists(Grant No.2013JQ0007)
文摘Flip buckets are commonly used to discharge flow away from a hydraulic structure into the downstream to dissipate energy.A new leak-floor flip bucket is presented,making the ski-jump water jet a typical long-narrow nappe.Based on the model experiments and numerical simulation,the flow pattern,formation process and mechanism of the leak-floor flip bucket are studied.The results show that cross section flow shape develops from the"Y-type"to"|-type",and this is because the natural pressure difference is generated when water flows through the leak-floor area and moves transversely from both sides to the center.Different from the slit-type flip bucket with sidewall contraction,the leak-floor flit bucket makes the water jet narrow and long without high pressure on the side walls of the flip bucket.Under the same jet length condition,the maximum sidewall pressure of the slit-type is 4.67 times that of the leak-floor flip bucket.The effects of flow discharge on the jet length are less significant for the leak-floor bucket than for the slit-type bucket.
基金Supported by the National Basic Research Program of China("973"Program)(Grant No.2007CB714105)the National Natural Science Foundation of China(Grant No.50539060)
文摘Bubble collecting, bubble holding and micro-bubble ejecting characteristics of pit structure and the influence of cavitation bubble on the development of erosion pit are investigated by means of highspeed photography experiments. Pits tend to collect and hold wandering cavitation bubbles. The air holding phenomenon of pits can be a destination of the incubation period in the process of cavitation erosion. The holding bubble tends to eject micro-bubbles from the top of holding cavitation bubble, making the pit a source of nuclei. With bubbles being held in pits, the diameters of pits increase rapidly. But in the given experiment condition, there is a specific stable value beyond which the diameter of pits will not increase. This characteristic will be helpful in understanding and predicting the cavitation erosion process.
基金supported by the National Natural Science Foundation of China (Grant No. 51379138)the National Basic Research Program of China (“973” Project) (Grant No. 2013CB035905)
文摘In hydraulic engineering,free-surface aeration is a natural phenomenon occurring in smooth channel flows.In self-aerated flows,a key aspect that has not yet been well understood is the formation mechanism of free-surface air entrainment.In this research,the process of free-surface entrapped deformation is analyzed theoretically and the critical radius of curvature for air entrainment is obtained,affected by flow mean velocity and depth.When the severity of local free-surface deformation exceeds the critical condition,the entrapped free surface encounters closure in the unstable deformation movement process,resulting in air entrainment.This inference agrees well with observed experimental results that are obtained from the processes of surface entrapped deformation and air entrainment captured by a high-speed camera-based data acquisition system.This agreement indicates that self-aeration occurs in low-velocity open-channel flows.It is also confirmed that free-surface turbulent deformation provides a mechanism for air entrainment.
