Experimental Study On The Hydrodynamic Characteristics Of The Oblique Stilling Basin

When the bridge or sluice is not perpendicular to the central line of the river while there is a stilling basin at the downstream,the oblique stilling basin will be applied in engineering practice.It not only meets the energy dissipation requirements,but also saves engineering investment compared with the traditional perpendicular stilling basin.At present,extensive researches have been carried out on the perpendicular stilling basin,however,less researches on the oblique stilling basin.Therefore,hydrodynamic characteristics of the oblique stilling basin were investigated in this thesis thus give the basis for engineering practice.Experiments methods and data analysis were carried out in this thesis.The oblique angles and depths of the stilling basin were mainly considered.The angles which were used in the test were 50°,60°,70°and 90°,and the angle of 90°was the comparative case.Furthermore,three depths cases were settled in the 50°stilling basin.Besides,five inflow discharges were applied in each case.Based on the data of the water depth,velocity and the fluctuating pressure,the characteristics of the hydraulic jump,velocity field and the fluctuating pressure on the bottom and side wall were analyzed.The main contents and results are as follows:?1?The investigation on the hydraulic jump characteristics of the oblique stilling basin was performed,and the influence of the oblique angles,the inflow discharges on the hydraulic jump characteristics and the water depth were analyzed.Results show that the distribution of hydraulic jumps in the oblique stilling basin is uneven.Positions of the hydraulic jump of each longitudinal section are different,and the lengths are also different.The hydraulic jump has an oblique angle with the flow direction.The smaller the oblique angle???is,the smaller angles between conjugate water depth and the flow direction??₁ and?₂?are,and the longer the hydraulic jump is.The smaller the oblique angle or inflow is,the closer the section hydraulic jump to the upstream is.Affected by the oblique angle,the water depth of the same cross section which parallel to the initial section of stilling basin are different in same discharge.As to the water level along each longitudinal section,different sections shows different changing laws.At the same oblique angle,the water depth on the right bank changes greatly,while it changes little on the left bank and the center line.The larger angle is,the more uniform the water surface is.The larger the discharge is,the more uneven the water surface on the left bank is.?2?The investigation on the bottom velocity and the vertical velocity of the oblique stilling basin were performed.After processing the three-dimensional velocity data,the distribution laws of the velocity at the bottom and vertical in the oblique stilling basin were obtained for different oblique angles and flow discharges.Compared with the perpendicular stilling basin,the longitudinal velocity of the left bank and the center line near the bottom is reduced,but this change shows to be not obvious in right bank.The larger the angle or the smaller the discharge is,the more uniform the bottom velocity is.The longitudinal or transverse velocity is large at the bottom of left bank and center line,while it is large at the surface of the right bank.The direction of transverse velocity has the following rules:Near the left bank,the transverse velocity points to the right bank in the 50°stilling basin,and vice versa in the 60°and 70°;near the center line,the direction is from the left bank to the right bank which not affected by the inflow angle;near the right bank,it is always from the right bank to the left bank.?3?The investigation on the fluctuating pressure of the bottom and the side wall of the oblique stilling basin were performed.The distribution law,probability density and spectrum characteristics of the fluctuating pressure at the three vertical sections on the bottom and the two side walls were obtained based on the analysis of the fluctuating pressure data.It is found that the fluctuating pressure on the bottom was reduced compared with the perpendicular stilling basin.The smaller the angle is,the smaller the fluctuating pressure on the side wall is.The probability density of fluctuating pressure at different positions were in accordance with normal distribution.?4?The formula of the conjugate water depth in the hydraulic jump of the oblique stilling basin was deducted,and the conjugate water depth correction coefficient was proposed.By using the conjugate water depth,the calculation formula of conjugate water depth correction coefficient of the oblique stilling basin is obtained through regression analysis.According to the frequency number and frequency distribution of the jump length coefficient obtained from the experiment,the range of the jump length coefficient in different angles was proposed,which can be used for reference in engineering design.