U形明渠流量与悬垂平板偏转角关系研究

为确定明渠流量与平板偏转角度的关系,本文研究了悬垂薄平板在明渠水流冲击作用下的动力学特性及平板偏转现象,分析绕轴自由旋转薄平板在水中的受力,将平板所受水流作用力竖直向上的分力假设为静水压力,应用动量定理与力矩平衡原理,推导了平板偏转角度α与流量Q之间的理论关系式,并在U型渠道上进行试验,验证理论公式的合理性。流量小于10 L/s时计算流量与实测流量的相对误差超过10%,其他均小于10%,流量大于17 L/s时误差均小于5%以内,测流范围在10~44 L/s,当悬垂薄平板与明渠横断面等大时,流量Q与偏转角度α存在单值对应关系,角度α随着流量Q的增大而增大;板前后水位差Δh随着角度α增大有逐渐减小并趋于定值(大概3 cm)的趋势,平板下水流流态随着平板偏转角度的增大由急流过渡为缓流;绕流阻力R随着雷诺数Re的增大而增大,阻力系数Cd随着雷诺数Re的增大而减小,平板偏转角度α与板前后水位差和阻力系数有关。

Relationship between U-shaped open channel discharge and deflection angle of draping thin plate

To explore the dynamic characteristics of a thin plate draping in open channel flow and its deflection to the flow, a relationship between the flow discharge and plate angle is determined, and flow forces acting on the plate and the moments about its axis are analyzed. With the vertical pressure on the plate assumed to be hydrostatic, an analytical relationship of its deflection angle α versus the channel discharge Q is derived by the momentum theorem and its moment equilibrium. A prototype plate is tested in a U-shaped channel to verify the analytical formula derived. It shows that relative to the measurements, the error in Q calculations is less than 10% at Q > 10 L/s and less than 5% at Q > 17 L/s. Thus, the range of Q for effective measurement is 10-44 L/s. When the shape and size of the plate nearly matches the channel cross-section, a well-defined relationship exists between Q and α. As α increases, the water level drop Δh across the plate decreases gradually and approaches a fixed value (about 3 cm), and the flow under the plate changes from supercritical to subcritical flow regime. With the Reynolds number increasing, the flow resistance R of the plate increases while its resistance coefficient Cd decreases. The plate angle α is related to the drop Δh and coefficient Cd .