scholarly journals Experimental and numerical investigation of flow over a spillway bend with different combinations of permeable spur dikes

2021 ◽  
Author(s):  
Jinmeng Yang ◽  
Zhenzhong Shen ◽  
Jing Zhang ◽  
Xiaomin Teng ◽  
Wenbing Zhang ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Dissipation Rate ◽  
Water Surface ◽  
Longitudinal Velocity ◽  
Flow Characteristics ◽  
Energy Dissipation Rate ◽  
Bottom Plate ◽  
Dye Tracing ◽  
Spur Dike ◽  
Spur Dikes

Abstract In this paper, the effects of different combinations of permeable spur dikes installed in the bend section of spillway on flow characteristics and energy dissipation rate were experimentally and numerically investigated. The results indicate that The permeable spur dikes installed in the spillway bend appreciably contributes to the improvement on the water surface uniformity, and the water surface uniformity can reach 90.13% with three permeable spur dikes installed in the bend. The permeable spur dike can lead to different degrees of decrease in the time-averaged longitudinal velocity in each zone of spillway bend. Different from previous study, no circulation zone is formed upstream and downstream of permeable spur dike due to the presence of permeable holes, and the flow upstream of permeable spur dikes could be divided into three distinctly different flow modes according to dye tracing. The presence of permeable spur dikes causes the concentration of TKE zone at concave bank of the spillway bend, except for TKE zone immediately next to the bottom plate. The TKE first increases and then decreases with the increase in the vertical distance from the bottom plate of the spillway bend, exhibiting a typical parabolic distribution. The energy dissipation rate in the spillway bend with permeable spur dike was calculated using a modified integral method, and the dissipation rate can reach as high as 21.08% with three spur dikes installed in the bend.

Three-component vorticity measurements in a turbulent grid flow

1998 ◽  
Vol 374 ◽  
pp. 29-57 ◽  
Author(s):  
R. A. ANTONIA ◽  
T. ZHOU ◽  
Y. ZHU
Keyword(s):  
Energy Dissipation ◽  
Dissipation Rate ◽  
Velocity Structure ◽  
Transverse Velocity ◽  
Longitudinal Velocity ◽  
Energy Dissipation Rate ◽  
Grid Turbulence ◽  
Local Isotropy ◽  
Velocity Increments ◽  
The Mean

All components of the fluctuating vorticity vector have been measured in decaying grid turbulence using a vorticity probe of relatively simple geometry (four X-probes, i.e. a total of eight hot wires). The data indicate that local isotropy is more closely satisfied than global isotropy, the r.m.s. vorticities being more nearly equal than the r.m.s. velocities. Two checks indicate that the performance of the probe is satisfactory. Firstly, the fully measured mean energy dissipation rate 〈ε〉 is in good agreement with the value inferred from the rate of decay of the mean turbulent energy 〈q2〉 in the quasi-homogeneous region; the isotropic mean energy dissipation rate 〈εiso〉 agrees closely with this value even though individual elements of 〈ε〉 indicate departures from isotropy. Secondly, the measured decay rate of the mean-square vorticity 〈ω2〉 is consistent with that of 〈q2〉 and in reasonable agreement with the isotropic form of the transport equation for 〈ω2〉. Although 〈ε〉≃〈εiso〉, there are discernible differences between the statistics of ε and εiso; in particular, εiso is poorly correlated with either ε or ω2. The behaviour of velocity increments has been examined over a narrow range of separations for which the third-order longitudinal velocity structure function is approximately linear. In this range, transverse velocity increments show larger departures than longitudinal increments from predictions of Kolmogorov (1941). The data indicate that this discrepancy is only partly associated with differences between statistics of locally averaged ε and ω2, the latter remaining more intermittent than the former across this range. It is more likely caused by a departure from isotropy due to the small value of Rλ, the Taylor microscale Reynolds number, in this experiment.

scholarly journals Hydraulic Characteristics and Numerical Simulation of the Entrance Section of Ladder-Shaped Spillway

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
X. B. Gu ◽  
Q. H. Wu ◽  
Y. Wang ◽  
H. X. Zhao
Keyword(s):  
Numerical Simulation ◽  
Energy Dissipation ◽  
Dissipation Rate ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Energy Dissipation Rate ◽  
Numerical Results ◽  
Experimental Results ◽  
Flow State ◽  
Hydraulic Characteristics

The ladder-shaped spillway in a certain reservoir junction is set as the engineering background in the paper. The hydraulic similarly model experiment and three-dimensional numerical simulation of hydraulic characteristics of water flow are performed. The outflow capacity, flow state analysis, velocity distribution, water surface line, pressure, and the energy dissipation rate are analyzed, and experimental results are compared with the numerical results. The conclusions demonstrate that the numerical results of the flow characteristics are very proximate to actual experimental results, the changeable law is the same, and their energy dissipation rate is basically consistent; it shows the feasibility of three-dimensional numerical simulation; the conclusions can provide the basis for the optimization about the flow state of the ladder-shaped spillway in the future.

scholarly journals Temperature Microstructure beneath Surface Gravity Waves

2004 ◽  
Vol 21 (11) ◽  
pp. 1747-1757 ◽  
Author(s):  
Craig L. Stevens ◽  
Murray J. Smith
Keyword(s):  
Energy Dissipation ◽  
Structure Function ◽  
Gravity Waves ◽  
Dissipation Rate ◽  
Water Surface ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Surface Gravity ◽  
Reliable Estimate ◽  
Surface Gravity Waves

Abstract Oceanic turbulence very near the water surface controls heat, momentum, energy, and mass transfer at the air–sea interface. This study examines the use of a rising temperature microstructure profiler for determination of the rate of turbulent energy dissipation ε beneath a water surface dominated by wind-driven surface gravity waves. Under short-fetch wind waves there is sufficient turbulent energy to generate an inertial-convective subrange. Thus, as well as the conventional Batchelor spectrum fitting approach, ε can be estimated using the temperature spectrum at lower wavenumbers. The inertial-convective subrange-derived turbulent energy dissipation rate εi compares well with the Batchelor spectrum method εb for higher dissipation rates. Sensor limitations mean that these estimates will be a lower bound. The highest dissipation rate estimates were in the uppermost data bin, indicating the importance of resolving right to the surface. Velocimeter results show that the surface waves modulate the rise velocity of the profiler, with variations reaching 75% of the deep water profiler speed. This increases the uncertainty in the transformation of spectra from frequency to wavenumber space using Taylor's frozen-field hypothesis. The use of an inertial convective structure-function-derived energy dissipation rate avoids this transformation. However, the structure function results are not encouraging as they provide a very poor estimate due to the sensitivity of the calculations and the low signal-to-noise ratio in the data. Repeated profiling illustrates the variability of turbulence intensity near the surface and also enables a reliable estimate of the background temperature gradient to be derived. This provides an improved estimate of vertical diffusion of heat.

The evolution of turbulent bursts: the b—ε model

1994 ◽  
Vol 5 (4) ◽  
pp. 537-557 ◽  
Author(s):  
M. Bertsch ◽  
R. Dal Passo ◽  
R. Kersner
Keyword(s):  
Partial Differential Equations ◽  
Energy Dissipation ◽  
Energy Density ◽  
Differential Equations ◽  
Dissipation Rate ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Self Similar ◽  
Similar Solutions ◽  
Semi Empirical

We study the semi-empirical b—ε model which describes the time evolution of turbulent spots in the case of equal diffusivity of the turbulent energy density b and the energy dissipation rate ε. We prove that the system of two partial differential equations possesses a solution, and that after some time this solution exhibits self-similar behaviour, provided that the system has self-similar solutions. The existence of such self-similar solutions depends upon the value of a parameter of the model.

scholarly journals 3D Numerical Study of the Flow Properties in a Double-Spur Dikes Field during a Flood Process

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1574 ◽  
Author(s):  
Xun Han ◽  
Pengzhi Lin
Keyword(s):  
Water Surface ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Field Measurements ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
River Bed ◽  
Hydrodynamic Evolution ◽  
Spur Dikes ◽  
Potential Damage

A 3D numerical model is developed to study the flow characteristics of a double-spur dikes field on Yangtze River during a flood process, which was presented by the variation of the flow condition. The model is based on Navier–Stokes (NS) equations, the porous medium method (PMM) is employed to treat the solid structures including the river bed surface, the volume of fluid (VOF) method is applied to track the motion of the water surface during the flood process, and large eddy simulation (LES) is adopted to capture the turbulence transport and dissipation. Using this model, the target reach’s flow field before the construction of double-spur dikes is simulated first, while the numerical results are compared to the field measurements on flow velocity and water surface level, and fairly good agreements are shown. Then, the model is applied to reproduce the hydrodynamic evolution during a flood process after double-spur dikes’ constructions, while the detailed 3D flow fields are obtained under some certain states with different submergence rates of the spur dikes; finally, the potential damage positions around these spur dikes are analyzed accordingly.

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