1、 中文 2200 字 外文原文 Experiments in Fluids 27 (1999) 339 350 Springer-Verlag 1999 Underflow of standard sluice gate A. Roth, W. H. Hager 1. Introduction Gates are a hydraulic structure that allows regulation of an upstream water elevation. Among a wide number of gate designs, the so-called standard gate
2、with a vertical gate structure containing a standard crest positioned in an almost horizontal smooth rectangular channel has particular significance in low head applications. Surface roughness of both the channel and the gate is small and thus insignificant. Standard gates are used both in laborator
3、ies and in irrigation channels, large sewers or in hydraulic structures. Compared to overflow structures, or in particular to the sharp-crested weir, standard gates have received scarce attention. The knowledge is particularly poor regarding the basic hydraulics, whereas studies relating to vibratio
4、n of these gates are available. The present project describes new findings on standard gate flow, involving: (1) Scale effects； (2) Coefficient of discharge； (3) Surface Ridge； (4) Features of shock waves； (5) Velocity field； (6) Bottom and gate pressure distributions； (7) Corner vortices； and (8) V
5、ortex intensities. A novel device to reduce shock waves in the downstream channel is also proposed. 2. Present knowledge The present knowledge on gates was recently summarized by Lewin (1995). There is a short chapter on vertical gates containing some information on discharge and contraction coeffic
6、ients,with a relatively large scatter of data. This reflects the present state, and gate flow is far from being understood from this point of view, therefore. Historical studies on underflow gates are available, and it is currently a common belief that the discharge character is tics of vertical gat
7、es have been detailed in the past century. This is definitely not the case, because of the accuracy of discharge measurement, and the small hydraulic models often used. Well known approaches include those of Boileau (1848), Bor-nemann (1871, 1880), containing summaries of the experiments of Lesbros
8、et al. Haberstroh (1890), Gibson (1920),Hurst and Watt (1925), Keutner (1932, 1935), Fawer (1937),Escande(1938), Gentilini(1941), and Smetana(1948). In these historical experimental studies, the exact geometrical configurations are often poorly specified, and the data are not always available. Detai
9、ls of gate fixation are also not described. The first modern study relating to free gate flow was conducted by Rajaratnam and Subramanya (1967). The coefficient of discharge was related to the difference of flow depths in the up- and downstream sections hCa, where o c h approach flow depth, coeffici
10、ent of contraction and o c agate opening. According to observations for both free and submerged flow C is exclusively a function of the relative gated opening a/h , and C increases slightly as a/h increases,o d o starting from C0.595. The effect of skin friction was stated d to be there as on for de
11、viations between computations based on the potential flow theory and observations. Rajaratnam (1977) conducted a second study on vertical gates in a rectangular channel 311mm wide, with gate openings between 26 and 101 mm. The axial free surface profile downstream of the gate section was shown to be
12、 self-similar. Nout sopoulos and Fanariotis (1978) pointed at the significant scatter of data relating to both coefficients of contraction and discharge. The deviations between observations and theory were attributed to the spatial flow characteristics, and the channels too small often used in labor
13、atories. Nago(1978) made observation sina400 mm wide rectangular channel with a gate opening of 60 mm. C was found to decrease with increasing relative gate opening, from 0.595 for a/h 0 to 0.52 for a/h0.50.o o.Rajarat namand Humphries (1982) considered the free flow characteristics upstream of a ve
14、rtical gate, as an addition to previous studies. The channel used was 311mm wide, and gate openings were a25 and 50 mm. Their data refer to the up stream recirculation zone, the bottom pressure distribution, and the velocity field. Montes (1997) furnished a solution for the 2D outflow using conforma
15、l mapping, compared the coefficient of contraction with experiments, and identified deviations due to viscosity effects. The surface profiles up and downstream rom the gate section were studied, exclusively in terms of gate opening. Energy losses across a gate were related to the boundary layer deve
16、lopment and the spatial flow features upstream from the gate. The pur- pose of this paper is to clarify several points of standard gate flow, including the discharge coefficient, the ridge position, the velocity and pressure distributions, and the shock wave development that was not at all considere
17、d up till now. These results may attract and guide numerical modelers of flow. Their results and approaches have not been reviewed here. 3 Experiments The experiments were conducted in a 500 mm wide and 7 m long horizontal and rectangular channel. The width of the approach channel was also reduced t
18、o b245 and 350mm.The right hand side wall and the channel bottom were coated with PVC, and the left hand side was of glass to allow for visualization. To improve the approach flow conditions, screens were inserted and surface waves were adequately reduced. The approach flow was thus without flow con
19、centrations, smooth and always in the turbulent smooth regime. The discharge was measured with a V-notch weir located down-stream of the channel, to within $1% or $0.1 ls1,whichever was larger. An aluminum gate 499mm wide, 600mm high and 10 mm thick was used, of which the crest was of standard geome
20、try, i.e. 2mm thick with a 45 bevel on the downstream side. The gate could be mounted with variable openings from the channel bottom. No gate slots were provided and water tightness was assured with a conventional tape. Only free gate flow was considered. The gate opening was varied from a10 120mm. Prefabricated elements of a specified height ($0.1 mm) were slid below the gate, and removed after the gate was positioned. This
