台阶式溢洪道滑行水流压强特性的试验研究

Experimental investigation on the pressure characteristics of skimming flow on stepped spillways

模型试验表明,台阶式溢洪道滑行水流压强在台阶上的分布规律是:在水平面,压强从台阶凹角向凸角先逐渐减小,其最小值在距凹角(0.3～0.5)倍步长处,然后开始回升,至(0.7～0.9)倍步长处压强升至最大,在凸角处又有所降低。竖直面,从凹角向上压强值由大逐渐减小,在步高为(0.5～1.0)范围内为负压区,负压值沿高度方向逐渐增大,至凸角下缘负压值最大。在沿程方向,压强呈波浪式分布,在相邻台阶上出现波峰和波谷。脉动压强强度和压强系数的变化规律与时均压强一致,且随来流量和台阶坡度增大而增大,在x/Lt≤0.4～0.5以前脉动压强强度沿程增大,随后有所减小。脉动压强的优势频率在0～2Hz之间,概率密度为偏态分布。

The conclusions about the pressure distribution on the steps are obtained from model tests. The pressure on the step's horizontal surface first falls down gradually from the nook and reaches a minimum at a distance of 0.3～0.5 step size away from the nook. Then, the pressure increases gradually and reaches a maximum at a distance of 0.7～0.9 step size from the nook. After the maximum point, it starts to decreases till the salient. The pressure on the vertical section decreases upward from the nook and becomes negative in the middle of the step. A zone in the range of 0.5～1.0 step size is called the negative zone. The absolute value of the negative pressure increases upward and its maximum occurs under the salient. The pressure distribution on the stepped spillway along the road is wavy, peaks and valleys occur alternatively on the steps. The law of the change of the fluctuating pressure intensity and the pressure index are consistant with that of the observed timeaveraged pressure, and increases along with the increase of the runoff and the slope of the spillway. The fluctuating pressure intensity increases along the road as x/Lt≤0.4～0.5, then decreases to some extent. The dominate frequencies of the fluctuating pressure lie the range of 0 to 2Hz. The probability function of the fluctuating pressure is of the abnornal distribution.