推移质运动对清水和宾汉体泥浆湍流结构的影响

通过试验研究了清水湍流和泥浆湍流中加入推移质后时均流速分布、脉动强度、概率密度分布、相关系数、频谱密度分布等的变化.试验结果证明,清水和泥浆湍流中加入推移质后时均流速减小,时均流速梯度增大,脉动加强.泥浆过渡区湍流上部为层流,有流核,加入推移质后,上部层流转变为湍流,流核消失.分析证明,这是由于推移质运动增大了雷诺应力和时均流速梯度,因而增大了时均流动向脉动传递的能量的缘故,清水湍流中加入推移质后脉速概率密度分布偏离正态,偏态系数加大.泥浆湍流中加入推移质后相关系数降低,脉动的随机性增大.泥浆湍流的脉动能量集中于低频脉动.由于推移质也可以吸收低频脉动能来支持其运动,所以加入推移质后泥浆湍流的低频脉动能量降低,高频脉动能量增大.

Effects of Bed Load Motion on Turbulence Structure of Water Flow and Bingham Mud Flow

The turbulence structure, velocity distribution, and spectral density distribution of water flow and Bingham mud flow are studied as the flows carry bed load particles. Experiments prove that average velocity decreases and average velocity gradient increases as the flows carry bed load. Turbulent intensity of flow carrying bed load is much larger than that without bed load. Bingham mud flow could become turbulent in the lower part of the flow while the upper part remains laminar as Reynolds number Rcm is between 2000 and 8000. The laminar flow in the upper part is transformed into turbulent flow as bed load particles are put into the flow.These phenomena could be interpreted by understanding the fact that bed load motion increases the Reynolds stress and average velocity gradient, therefore, the energy transmitted from time-averaged motion into turbulence is largely enhanced. The probability density distribution of fluctuating velocity of water flow carrying bed load deviates far from normal distribution. Bed load motion in Binghafn mud flow reduces the autocorrelation coefficient of the turbulent flow. Turbulent energy in Bingham mud flow concentrates in low-frequency (0-1 Hz) turbulent eddies. After adding coarse sand into the mud flow which moves as bed load, the turbulent energy in low-frequency decreases and that in high-frequency turbulence increases, because bed load motion transports energy from low-frequency turbulence to high-frequency turbulence.