Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow...Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow properties develop gradually, accompanied by the change of microscopic air–water structures. In this article, representational experimental studies on macroscopic and microscopic characteristics of self-aerated open-channel flows are summarized and compared. The isolated effect of the flow Reynolds number and air quantity on the differences in air count rate and chord size are analyzed and discussed. The results show that the characterized flow depth y, affected by the turbulence transfer, is a specific criterion to distinguish the interior air–water structure development. Two distinct linear trends of self-aeration are found, depending on the y/yvariation with a breaking point at Cmean =0.50. The air count rate and size scale in self-aerated flows are affected by the air quantity of self-aerated flows, even with identical flow Reynolds numbers. Thus, a specific parameter is proposed to assess the air–water structures and a series of self-similarity relationships in self-aeration properties are obtained. The link between macroscopic and microscopic air–water properties results in significant scale effect on air–water structures in self-aerated flows.展开更多
In this paper,a kind of composite microtube,which is made from superfine silk powder and polyurethane,reinforced by polyster and spandex tubular fabrics,was examined.The cross-section of composite microtubes were micr...In this paper,a kind of composite microtube,which is made from superfine silk powder and polyurethane,reinforced by polyster and spandex tubular fabrics,was examined.The cross-section of composite microtubes were microporous,and micropores were uniform distributed,the inner surface was relatively smooth.The results showed that the wall thickness of composite microtubes increased,which led to the strength,the breaking work and the initial modulus incresead;that the spandex content increased brought about the initial modulus and the breaking work decreased,but the breaking extension and the breaking load were firstly increased and then decreased;and all the mechanical properties decreased as the SFSP content increased.展开更多
The hydraulic jump is a typical sudden change for mountain river areas.The effects of local hydraulic jumps on the particle transport capacity decrease and local flow resistance increase cannot be ignored as the sedim...The hydraulic jump is a typical sudden change for mountain river areas.The effects of local hydraulic jumps on the particle transport capacity decrease and local flow resistance increase cannot be ignored as the sediment deposition disaster can amplify the flash flood disaster.The present research investigates the influences of a hydraulic jump on the individual particle movement and sediment deposition in a laboratory flume.The overall processes of a single particle movement are captured by a high-speed camera.The distribution of sediment deposition along the hydraulic jump is obtained statistically.The results show that both the particle size and the ratio of the upstream and downstream Froude numbers affect the particle motion process.A single particle coming from upstream gradually decelerates and finally stops at the hydraulic jump section because of hydraulic jump resistance.The particle acceleration first increases and then decreases during the time-domain process,and the attenuation trends are fast with the increase of ratio of upstream and downstream of Froude numbers.The increase of the maximum acceleration with sediment flows follows a linear trend approximately,which indicates that the kinetic features of the single sand particle are determined by the coupling effects of the hydraulic jump resistance and the sand dynamic properties.With the increase of sediment rate and sand particle size,the resistance effect of hydraulic jump on sediment deposition rate along the flow direction gets strong and the sediment deposition area is mainly located upstream of the hydraulic jump region.The present study shows that the possible sediment supply upstream must be obtained for identifying the disaster risk combined with the local hydraulic jump conditions.Further researches about the detailed critical condition deduced from the relationship between the water flow and sediment deposition are required to confirm and extrapolate present results to other applications.展开更多
This paper presents results of model tests for the landslide dam failure of a single dam and cascade dams in a sloping channel. The dams were designed to be regular trapezoid with fine sand. A new measuring method nam...This paper presents results of model tests for the landslide dam failure of a single dam and cascade dams in a sloping channel. The dams were designed to be regular trapezoid with fine sand. A new measuring method named the labeled line locating method was used to digitalize the captured instantaneous pictures. Under two different inflow discharges, the morphological evolution and the flow patterns during one dam failure and the failure of cascade dams were investigated. The results indicate that when the inflow discharge is large, the deformation pattern of the downstream dam is similar to that of the upstream dam, and both dams are characterized with the overtopping scour throughout the dam failure process. When the inflow discharge is small, the upstream dam is scoured mainly through a sluice slot formed by the longitudinal incision, and the downstream dam is characterized with the overtopping scour. The data set presented in this paper can be used for the validation of numerical models and provide a reference for the flood risk management of cascade landslide dams.展开更多
The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical c...The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction.The bubble-bubble interaction can be considered in two different conditions.The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small,and away from the air bubble if the air bubble is relatively large.The two zones are identified in the bubble-boundary interaction,and they are the danger zone and the safety zone.The relative position,the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction,which can be considered in several conditions according to the responses of the bubbles.Air jets are found to penetrate into the cavitation bubbles.The cavitation bubble and the air bubble（air jet） move in their own way without mixing.The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary.The influence of the air bubble and the influence of the boundary may be combined,like some thing of a vector.展开更多
Dam break can cause a significant disaster in the downstream, especially, in a valley with cascade reservoirs, which would aggravate the disaster extent. The experimental studies of the dam-break flow of cascade reser...Dam break can cause a significant disaster in the downstream, especially, in a valley with cascade reservoirs, which would aggravate the disaster extent. The experimental studies of the dam-break flow of cascade reservoirs are few and far between at the present, Most of related studies concern the failure of a single dam.. This article presents an experimental study of the characteristics of an instantly filled dam-break flow of cascade reservoirs in a rectangular glass flume with a steep bottom slope. A new method was used to simulate the sudden collapse of the dam. A series of sensors for automatic water-levels were deployed to record the rapid water depth fluctuation. The experimental results show that, the ratio of the initial water depth of the downstream reservoir to that of the upstream reservoir would greatly affect the flood peak water depth in the downstream reservoir area and in the stream channel behind the downstream dam, while the influence of the dam spacing is insignificant. In addition, the comparison between the single reservoir and the cascade reservoirs shows some difference in the dam-break flow pattern and the stage hydrograph at the corresponding gauging points.展开更多
The interaction of an air bubble （isolated in water or attached to a boundary） with shock waves induced by electric sparks is investigated by high-speed photography. The interaction is closely related to the counter...The interaction of an air bubble （isolated in water or attached to a boundary） with shock waves induced by electric sparks is investigated by high-speed photography. The interaction is closely related to the counter-jet induced by the impact of shock waves. The formation of a counter-jet in an air bubble is related to the liquid jet formed in the same air bubble, but the mechanism is different with that of the counter-jet formation in a collapsing cavitation bubble. The formation of a counter-jet in an air bubble is related to discharge energy, air bubble size and radius of shock wave. With a given energy of the spark discharge, the formation of a counter-jet in an air bubble is related to δ / ε （the ratio of the dimensionless bubble-bubble distance to the dimensionless air bubble radius）. The counter-jet will only be produced when δ / ε is in the range of 1.2-2.2. The counter-jet in an air bubble is of an important nuclei-generating mechanism.展开更多
The flow field of a river with complicated boundaries is simulated by dividing the calculation domain into several subdomains and using the depth-averaged k-ε turbulence model. The complicated topographic conditions ...The flow field of a river with complicated boundaries is simulated by dividing the calculation domain into several subdomains and using the depth-averaged k-ε turbulence model. The complicated topographic conditions in this paper include bar, confluence, narrow, bay and bend, etc. The lands emerging from the water surface are treated as blocked-off regions. The calculation is achieved at both the low and the high water levels. The velocity profiles along cross-sections are measured at the high water level in physical model. The calculated and measured velocity profiles are in agreement.展开更多
The characteristics of the impinging pressure at the jet equipment where the maximum jet velocity can reach 50m/s were studied. By comparing the impinging pressure with the one measured at the low velocity conditions,...The characteristics of the impinging pressure at the jet equipment where the maximum jet velocity can reach 50m/s were studied. By comparing the impinging pressure with the one measured at the low velocity conditions, two conclusions of the scale effect are drawn： firstly, the velocity attenuation degree is smaller than that of low velocity jet, and secondly, the relative impinging width is narrower than that of low-velocity jet. The reasons of the scale effect of the impinging pressure were elucidated through numerical simulation.展开更多
For the 90° equal-width open-channel junction flow, the Reynolds averaged Navier-Stokes equations are solved while using the 3-D κ- ω model. The mean flow pattern and the secondary current are obtained. The mod...For the 90° equal-width open-channel junction flow, the Reynolds averaged Navier-Stokes equations are solved while using the 3-D κ- ω model. The mean flow pattern and the secondary current are obtained. The model is validated by experimental data, and then applied to investigate the effect of the discharge ratio on the shape of separation zone shape, the cross-sectional mean flow angle and the contraction coefficient. The results are fairly close to those of the prior studies. The numerical modeling is both less time-consuming and less expensive to obtain the various flow parameters needed for engineering design.展开更多
基金financially supported by the National Key Research and Development Program of China(Grant No.2016YFC0401901)the National Natural Science Foundation of China(Grant Nos.51379138 and 51609162)
文摘Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow properties develop gradually, accompanied by the change of microscopic air–water structures. In this article, representational experimental studies on macroscopic and microscopic characteristics of self-aerated open-channel flows are summarized and compared. The isolated effect of the flow Reynolds number and air quantity on the differences in air count rate and chord size are analyzed and discussed. The results show that the characterized flow depth y, affected by the turbulence transfer, is a specific criterion to distinguish the interior air–water structure development. Two distinct linear trends of self-aeration are found, depending on the y/yvariation with a breaking point at Cmean =0.50. The air count rate and size scale in self-aerated flows are affected by the air quantity of self-aerated flows, even with identical flow Reynolds numbers. Thus, a specific parameter is proposed to assess the air–water structures and a series of self-similarity relationships in self-aeration properties are obtained. The link between macroscopic and microscopic air–water properties results in significant scale effect on air–water structures in self-aerated flows.
基金State Natural Sciences Fundgrant number:50873079+1 种基金National Major Foudamental Research Program of Chinagrant number:2009CB526402
文摘In this paper,a kind of composite microtube,which is made from superfine silk powder and polyurethane,reinforced by polyster and spandex tubular fabrics,was examined.The cross-section of composite microtubes were microporous,and micropores were uniform distributed,the inner surface was relatively smooth.The results showed that the wall thickness of composite microtubes increased,which led to the strength,the breaking work and the initial modulus incresead;that the spandex content increased brought about the initial modulus and the breaking work decreased,but the breaking extension and the breaking load were firstly increased and then decreased;and all the mechanical properties decreased as the SFSP content increased.
基金supported by the National Natural Science Foundation of China(51939007,51979183)。
文摘The hydraulic jump is a typical sudden change for mountain river areas.The effects of local hydraulic jumps on the particle transport capacity decrease and local flow resistance increase cannot be ignored as the sediment deposition disaster can amplify the flash flood disaster.The present research investigates the influences of a hydraulic jump on the individual particle movement and sediment deposition in a laboratory flume.The overall processes of a single particle movement are captured by a high-speed camera.The distribution of sediment deposition along the hydraulic jump is obtained statistically.The results show that both the particle size and the ratio of the upstream and downstream Froude numbers affect the particle motion process.A single particle coming from upstream gradually decelerates and finally stops at the hydraulic jump section because of hydraulic jump resistance.The particle acceleration first increases and then decreases during the time-domain process,and the attenuation trends are fast with the increase of ratio of upstream and downstream of Froude numbers.The increase of the maximum acceleration with sediment flows follows a linear trend approximately,which indicates that the kinetic features of the single sand particle are determined by the coupling effects of the hydraulic jump resistance and the sand dynamic properties.With the increase of sediment rate and sand particle size,the resistance effect of hydraulic jump on sediment deposition rate along the flow direction gets strong and the sediment deposition area is mainly located upstream of the hydraulic jump region.The present study shows that the possible sediment supply upstream must be obtained for identifying the disaster risk combined with the local hydraulic jump conditions.Further researches about the detailed critical condition deduced from the relationship between the water flow and sediment deposition are required to confirm and extrapolate present results to other applications.
基金supported by the National Basic Research and Development Program of China(973 Program,Grant No.2007CB714105)the National Natural Science Foundation of China(Grant No.50909067)
文摘This paper presents results of model tests for the landslide dam failure of a single dam and cascade dams in a sloping channel. The dams were designed to be regular trapezoid with fine sand. A new measuring method named the labeled line locating method was used to digitalize the captured instantaneous pictures. Under two different inflow discharges, the morphological evolution and the flow patterns during one dam failure and the failure of cascade dams were investigated. The results indicate that when the inflow discharge is large, the deformation pattern of the downstream dam is similar to that of the upstream dam, and both dams are characterized with the overtopping scour throughout the dam failure process. When the inflow discharge is small, the upstream dam is scoured mainly through a sluice slot formed by the longitudinal incision, and the downstream dam is characterized with the overtopping scour. The data set presented in this paper can be used for the validation of numerical models and provide a reference for the flood risk management of cascade landslide dams.
基金supported by the Ministry of Science and Technology of China (Grant Nos. 2007CB714105 and 2008BAB29B04)
文摘The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction.The bubble-bubble interaction can be considered in two different conditions.The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small,and away from the air bubble if the air bubble is relatively large.The two zones are identified in the bubble-boundary interaction,and they are the danger zone and the safety zone.The relative position,the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction,which can be considered in several conditions according to the responses of the bubbles.Air jets are found to penetrate into the cavitation bubbles.The cavitation bubble and the air bubble（air jet） move in their own way without mixing.The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary.The influence of the air bubble and the influence of the boundary may be combined,like some thing of a vector.
基金Project supported by the National Basic Research Program of China(973 Program,Grant No.2007CB714105)the National Natural Science Foundation of China(Grant No.50909067)
文摘Dam break can cause a significant disaster in the downstream, especially, in a valley with cascade reservoirs, which would aggravate the disaster extent. The experimental studies of the dam-break flow of cascade reservoirs are few and far between at the present, Most of related studies concern the failure of a single dam.. This article presents an experimental study of the characteristics of an instantly filled dam-break flow of cascade reservoirs in a rectangular glass flume with a steep bottom slope. A new method was used to simulate the sudden collapse of the dam. A series of sensors for automatic water-levels were deployed to record the rapid water depth fluctuation. The experimental results show that, the ratio of the initial water depth of the downstream reservoir to that of the upstream reservoir would greatly affect the flood peak water depth in the downstream reservoir area and in the stream channel behind the downstream dam, while the influence of the dam spacing is insignificant. In addition, the comparison between the single reservoir and the cascade reservoirs shows some difference in the dam-break flow pattern and the stage hydrograph at the corresponding gauging points.
基金supported by the National Science and Technology Support Plan of China (Grant No.2008BAB29B04)the National Basic Research Program of China (973 Program,Grant No. 2007CB714105)+1 种基金the National Natural Science Foundation of China (Grant No. 11174315)the National Science and Technology Major Project ofChina (Grant No. 2011ZX05032-003)
文摘The interaction of an air bubble （isolated in water or attached to a boundary） with shock waves induced by electric sparks is investigated by high-speed photography. The interaction is closely related to the counter-jet induced by the impact of shock waves. The formation of a counter-jet in an air bubble is related to the liquid jet formed in the same air bubble, but the mechanism is different with that of the counter-jet formation in a collapsing cavitation bubble. The formation of a counter-jet in an air bubble is related to discharge energy, air bubble size and radius of shock wave. With a given energy of the spark discharge, the formation of a counter-jet in an air bubble is related to δ / ε （the ratio of the dimensionless bubble-bubble distance to the dimensionless air bubble radius）. The counter-jet will only be produced when δ / ε is in the range of 1.2-2.2. The counter-jet in an air bubble is of an important nuclei-generating mechanism.
文摘The flow field of a river with complicated boundaries is simulated by dividing the calculation domain into several subdomains and using the depth-averaged k-ε turbulence model. The complicated topographic conditions in this paper include bar, confluence, narrow, bay and bend, etc. The lands emerging from the water surface are treated as blocked-off regions. The calculation is achieved at both the low and the high water levels. The velocity profiles along cross-sections are measured at the high water level in physical model. The calculated and measured velocity profiles are in agreement.
基金Project supported by the National Natural Science Foundation of China (Grant No :50325928) .
文摘The characteristics of the impinging pressure at the jet equipment where the maximum jet velocity can reach 50m/s were studied. By comparing the impinging pressure with the one measured at the low velocity conditions, two conclusions of the scale effect are drawn： firstly, the velocity attenuation degree is smaller than that of low velocity jet, and secondly, the relative impinging width is narrower than that of low-velocity jet. The reasons of the scale effect of the impinging pressure were elucidated through numerical simulation.
基金supported by the National Basic Research Program of China (973 Program, Grant No. 2007CB714705)the National Science Foundation of Fujian Province (Grant No. E0710013)
文摘For the 90° equal-width open-channel junction flow, the Reynolds averaged Navier-Stokes equations are solved while using the 3-D κ- ω model. The mean flow pattern and the secondary current are obtained. The model is validated by experimental data, and then applied to investigate the effect of the discharge ratio on the shape of separation zone shape, the cross-sectional mean flow angle and the contraction coefficient. The results are fairly close to those of the prior studies. The numerical modeling is both less time-consuming and less expensive to obtain the various flow parameters needed for engineering design.
