Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows...Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical simulations.The depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain.The instantaneous coherent structures were presented by the Q criterion method.The impact of hr on flow structure and turbulence charac-teristics was analyzed.The results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region.展开更多
This study focuses on the effects of one-line emergent natural tree（Cupressus Macrocarpa） planted at the edge of the floodplain in a compound open-channel flow. The flow velocity and water level are measured and use...This study focuses on the effects of one-line emergent natural tree（Cupressus Macrocarpa） planted at the edge of the floodplain in a compound open-channel flow. The flow velocity and water level are measured and used to analyze the flow structure. The time averaged and depth-averaged streamwise velocity distributions with root mean square（rms） and time series of streamwise velocity distrbution are analyzed. The velocity distribution considerably changes along the compound channel. The streamwise velocity distribution fits with logarithmic distribution in the non-vegetated case, but for vegetated cases, the streamwise velocity distribution shows S shaped profile at the 1/3 part of floodplain（/3）B_f and main channel（/3）B_m close to the boundary between floodplain and main channel. Additionally, it is obtained that the presence of tree line increases turbulence intensity over the compound open-channel. Moreover, an oscillation period is obtained in the flow caused by tree line by analyzing time series of the streamwise velocity distribution. The oscillation is present everywhere in the floodplain and present at almost/3 B_m part of the main channel which is close to the junction between floodplain and main channel.展开更多
Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY mode...Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY model). Simulation results were compared with observation of (i) turbulent flows in alternating point-bar type channel bends with rectangular sections, and (ii) straight open channel flows with compound cross-sections. Based on calculations of the impact of various channel curvatures on turbulence characteristics, accuracy of the three turbulence models was analyzed with observed data as a qualitative reference. It has been found out that the Launder and Ying model and the nonlinear k-ε Model are able to predict the same general trend as measured data, and the simulation of the effect of the centrifugal force on the formation of secondary currents produces a correct pattern.展开更多
采用数值模拟方法研究了复式断面和矩形断面60°弯道明渠的流场结构。自由水面的捕捉采用VOF(Volume of Fluid)法,雷诺时均N-S方程采用雷诺应力模型封闭。对两种断面渠型水力特性的模拟结果进行了比较,结果表明:复式断面弯道明渠在...采用数值模拟方法研究了复式断面和矩形断面60°弯道明渠的流场结构。自由水面的捕捉采用VOF(Volume of Fluid)法,雷诺时均N-S方程采用雷诺应力模型封闭。对两种断面渠型水力特性的模拟结果进行了比较,结果表明:复式断面弯道明渠在弯道横断面上存在着多涡结构;滩地上的流速大于主槽上的流速;凹岸和凸岸上的自由液面水位差要比矩形断面的小;水流在渠底的横向运动强度要比矩形断面的大;弯道内外侧的压力差也与矩形断面有所不同。展开更多
基金supported by the Fundamental Research Funds for the Central Universities(Grants No.B200202116 and B200204044)the National Natural Science Foundation of China(Grant No.51879086)the 111 Project from the Minstry of Education and State Administration of Foreign Expert Affairs of China(Grant No.B17015).
文摘Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical simulations.The depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain.The instantaneous coherent structures were presented by the Q criterion method.The impact of hr on flow structure and turbulence charac-teristics was analyzed.The results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region.
基金the funding of the research project (MF14010) from Adnan Menderes University which allows establishing the experiment flume in the laboratory
文摘This study focuses on the effects of one-line emergent natural tree（Cupressus Macrocarpa） planted at the edge of the floodplain in a compound open-channel flow. The flow velocity and water level are measured and used to analyze the flow structure. The time averaged and depth-averaged streamwise velocity distributions with root mean square（rms） and time series of streamwise velocity distrbution are analyzed. The velocity distribution considerably changes along the compound channel. The streamwise velocity distribution fits with logarithmic distribution in the non-vegetated case, but for vegetated cases, the streamwise velocity distribution shows S shaped profile at the 1/3 part of floodplain（/3）B_f and main channel（/3）B_m close to the boundary between floodplain and main channel. Additionally, it is obtained that the presence of tree line increases turbulence intensity over the compound open-channel. Moreover, an oscillation period is obtained in the flow caused by tree line by analyzing time series of the streamwise velocity distribution. The oscillation is present everywhere in the floodplain and present at almost/3 B_m part of the main channel which is close to the junction between floodplain and main channel.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 50179015, 59879009, 50221903)
文摘Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY model). Simulation results were compared with observation of (i) turbulent flows in alternating point-bar type channel bends with rectangular sections, and (ii) straight open channel flows with compound cross-sections. Based on calculations of the impact of various channel curvatures on turbulence characteristics, accuracy of the three turbulence models was analyzed with observed data as a qualitative reference. It has been found out that the Launder and Ying model and the nonlinear k-ε Model are able to predict the same general trend as measured data, and the simulation of the effect of the centrifugal force on the formation of secondary currents produces a correct pattern.
文摘采用数值模拟方法研究了复式断面和矩形断面60°弯道明渠的流场结构。自由水面的捕捉采用VOF(Volume of Fluid)法,雷诺时均N-S方程采用雷诺应力模型封闭。对两种断面渠型水力特性的模拟结果进行了比较,结果表明:复式断面弯道明渠在弯道横断面上存在着多涡结构;滩地上的流速大于主槽上的流速;凹岸和凸岸上的自由液面水位差要比矩形断面的小;水流在渠底的横向运动强度要比矩形断面的大;弯道内外侧的压力差也与矩形断面有所不同。
