By choosing a PVC slice to simulate flexible vegetation, we carried out experiments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter （micro ADV） was used to measure local flow...By choosing a PVC slice to simulate flexible vegetation, we carried out experiments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter （micro ADV） was used to measure local flow velocities and Reynolds stress. The results show that hydraulic characteristics in non-vegetation and vegetation layers are totally different. In a region above the vegetation, Reynolds stress distribution is linear, and the measured velocity profile is a classical logarithmic one. Based on the concept of new-riverbed, the river compression parameter representing the impact of vegetation on river is given, and a new assumption of mixing length expression is made. The formula for time-averaged velocity derived from the expression requires less parameters and simple calculation, and is useful in applications.展开更多
This paper aims to understand the flow structure around submerged dike in the main channel and flood plain of a compound cross section. The study undertaken to develop this understanding was carried out in a laborator...This paper aims to understand the flow structure around submerged dike in the main channel and flood plain of a compound cross section. The study undertaken to develop this understanding was carried out in a laboratory flume using a submerged vane installed at a 90 degree angle to the bank. In order to study the flow structures, the flow velocity was measured using a three-dimensional Acoustic Doppler Velocity meter (micro-ADV) with data collection rate of 50 Hz. These flow velocity measurements were taken at 500 points on a regular grid. As the tests were undertaken with turbulent flow, these conditions were subcritical. Furthermore, all the tests were undertaken using a fixed bed. The results obtained showed that the momentum transfer and the kinetic energy reduced in two directions. Also the energy and momentum coefficients decreased significantly with the installation of the submerged vane inside the main channel. Finally, streamlines were found to deviate from the side walls of channel into the main channel.展开更多
An experiment was conducted to examine the near-field behavior of negatively buoyant planar jets in flowing environment. Hot water jet was projected downwards at dif fercnt angles from a slot into a uniform cross flow...An experiment was conducted to examine the near-field behavior of negatively buoyant planar jets in flowing environment. Hot water jet was projected downwards at dif fercnt angles from a slot into a uniform cross flow. Micro Acoustic Doppler Velocimeter （Micro ADV） system is used to measure the velocity and turbulent fluxes of Reynolds stresses. The whole field temperatures were measured with fast response thermocouples. Pure jets experiments were made also to study the effect of buoyancy in negatively buoyant jets. It is found that the influenced area of hot jets is larger than which of pure jets when the jet angle is 90° and the influenced area of hot jets is smaller than which of pure jets when the jet angle is 45°. The difference is not obvious at 60° angle jets. This means that the rising of temperature has effect not only on negatively buoyancy, but also on the intensity of turbulence. The contrast of these two influences dominates the trend of jet flow.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50679061, 50709025,50749031)
文摘By choosing a PVC slice to simulate flexible vegetation, we carried out experiments in an open channel with submerged flexible vegetation. A 3D acoustic Doppler velocimeter （micro ADV） was used to measure local flow velocities and Reynolds stress. The results show that hydraulic characteristics in non-vegetation and vegetation layers are totally different. In a region above the vegetation, Reynolds stress distribution is linear, and the measured velocity profile is a classical logarithmic one. Based on the concept of new-riverbed, the river compression parameter representing the impact of vegetation on river is given, and a new assumption of mixing length expression is made. The formula for time-averaged velocity derived from the expression requires less parameters and simple calculation, and is useful in applications.
文摘This paper aims to understand the flow structure around submerged dike in the main channel and flood plain of a compound cross section. The study undertaken to develop this understanding was carried out in a laboratory flume using a submerged vane installed at a 90 degree angle to the bank. In order to study the flow structures, the flow velocity was measured using a three-dimensional Acoustic Doppler Velocity meter (micro-ADV) with data collection rate of 50 Hz. These flow velocity measurements were taken at 500 points on a regular grid. As the tests were undertaken with turbulent flow, these conditions were subcritical. Furthermore, all the tests were undertaken using a fixed bed. The results obtained showed that the momentum transfer and the kinetic energy reduced in two directions. Also the energy and momentum coefficients decreased significantly with the installation of the submerged vane inside the main channel. Finally, streamlines were found to deviate from the side walls of channel into the main channel.
基金Project supported by the National Natural Science Foundation of China ( Grant No : 50279037) and Open ResearchFund Programof State Key Laboratory of Water Resources and Hydropower Engineering Science (Grant No :2005C011) .
文摘An experiment was conducted to examine the near-field behavior of negatively buoyant planar jets in flowing environment. Hot water jet was projected downwards at dif fercnt angles from a slot into a uniform cross flow. Micro Acoustic Doppler Velocimeter （Micro ADV） system is used to measure the velocity and turbulent fluxes of Reynolds stresses. The whole field temperatures were measured with fast response thermocouples. Pure jets experiments were made also to study the effect of buoyancy in negatively buoyant jets. It is found that the influenced area of hot jets is larger than which of pure jets when the jet angle is 90° and the influenced area of hot jets is smaller than which of pure jets when the jet angle is 45°. The difference is not obvious at 60° angle jets. This means that the rising of temperature has effect not only on negatively buoyancy, but also on the intensity of turbulence. The contrast of these two influences dominates the trend of jet flow.
