| This article focuses on the spillway of the Mengyejiang hydropower station and selects the optimal shape through observations of the flow patterns.The recommended design is then tested through hydraulic model experiments to measure and analyze the spillway’s flow patterns,discharge capacity,water surface elevation,pressure,velocity,downstream erosion,etc.The results are used to further optimize the spillway’s design,particularly where it falls short of flood discharge and energy dissipation requirements.Numerical simulation is used to analyze the flow field of the spillway and validate the rationality of the spillway’s shape and layout.The findings of this study can provide reference for engineering design,and the main research results are as follows:(1)Through the observation of the flow pattern of the spillway inlet,it was found that in the original left guide wall design,there was serious flow separation at the top of the guide wall and the pier head.Therefore,the length of the straight section of the left guide wall was shortened,and the wall was expanded towards the dam body.The original shape,defined by the equation x2/302+y2/152=1,was modified to a quarter ellipse with the equation x2/362+y2/262=1.Additionally,the semi-circular pier head was changed to a combination of two circular arcs with a sharp angle.The modified shape significantly reduced flow separation and made the water flow at the entrance to the spillway smooth.(2)Through analysis and comparison of the flow patterns of the spillway’s crest gate,the parallel double orifice design of the spillway’s crest gate was optimized to a differentiated design.This ensured that the water tongue of the spillway was well-captured in the chute under all working conditions,and that it did not interfere with the jet flow from the narrow slit at the flood discharge orifice.The reasonable distribution of the two crest gates on the downstream channel effectively reduced the inflow width per unit area and allowed the water flow to form a certain longitudinal stretching and diffusion in the air,avoiding concentrated scouring and reducing the depth of scour holes.(3)The recommended design of the spillway was verified to meet the requirements of flood discharge capacity.However,for sections of the spillway that did not meet the safety requirements during high flow,such as the edge walls of the spillway and the irregularly shaped crest gates,optimization was carried out by increasing their height.There are high-velocity flows in the spillway’s discharge orifice and crest gate,and the minimum cavitation number is only 0.31.During construction,the surface roughness of these areas must be strictly controlled.The downstream area generates eddies,which are detrimental to energy dissipation and scouring.When the downstream flow velocity is high,it causes some scouring on both sides of the slope.Protective measures should be taken.(4)The erosion test was conducted on the downstream of the spillway,and the erosion protection range for the downstream was determined.The elevations of the deepest scour points for floods that occur once in 30 years and once in 100 years are 682.65m and 679.65m,respectively.Some scouring occurred at the end of the spillway protection slab,so,the bottom of the end tooth wall of the spillway apron should be extended into the rock foundation or the elevation should not be higher than 680.00 m.(5)A detailed analysis of the flow field in the spillway was carried out using numerical simulation methods,including flow pattern,water surface elevation,flow velocity,pressure,and water tongue height.To address the limitations of the physical model experiments,the water tongue velocity and inlet velocity were studied,and an optimization range for increasing the spillway sidewall height was proposed.The water pressure in the spillway was further reviewed,and the results showed that there was no negative pressure at the spillway crest,with only a value of-0.07×9.8kPa observed,and the pressure values were all positive with a smooth trend,consistent with the model test results,indicating that the design of the spillway crest curve,chute,and baffle was reasonable. |
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