微灌离心分离器内部流场分布数值模拟

摘要

在缺水地区，利用高含沙水作为微灌水源的条件下，低浓度混合多相流模型已不能适用于微灌用离心分离器的数值模拟。该文以高含沙水作为微灌水源，结合离心分离器的结构参数，在流体力学基本方程基础上，通过网格划分和边界条件设定，采用有限体积法进行离散和求解，控制方程采用k-ε模型模拟分析了离心分离器的内部流场特征，并通过试验验证数值模拟成果，模拟值与试验实测值相对误差在10%以内，说明数值模拟采用的算法和模型是合理的。在试验验证的基础上，模拟分析了高含沙水为微灌水源的条件下，离心分离器的速度、湍动能以及静压分布，结果表明：离心分离器内速度分布主要有切向速度、轴向速度和径向速度，沿径向方向具有一定的对称性；离心分离器内湍动能分布具有一定的对称性，由轴中间向器壁两侧逐渐变小；静压分布具有一定的对称性性，由器壁两侧向轴中心逐渐减少。结果可为微灌用离心分离器特性参数的优化提供依据。%Centrifugal separator is one kind of filtration equipment that can separate the sediment from high-silt content water based on principles of rotational flow and centrifugal force. In recent years, research on numerical simulation of centrifugal separator is mostly in the fields of petroleum and chemical industry, and focuses on low concentration and mixture multiphase flow model. When using high-silt content water as micro-irrigation water source in water shortage areas, there will be high-silt content water near the centrifugal separator wall and underflow, in such case, low concentration and mixture multiphase flow model is not applicable to the numerical simulation of centrifugal separator that has used for micro-irrigation. Using high-silt content water as micro-irrigation water source, combined with the structure parameters of centrifugal separator, in this article, we established hydromechanics fundamental equation and used finite volume method to discretize and solve it. High concentration turbulence model was selected to analyze the internal flow field characteristics of the centrifugal separator by dividing grids and setting boundary conditions.Numerical simulation results were verified through an experiment, which was carried out in December 2014 at the State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University. XLF200 centrifugal separator was selected with the cylinder diameter of 200 mm, the water outlet diameter of 65 mm, the water inlet diameter of 50 mm, and the bottom outlet diameter of 50 mm. Three different working conditions including the bottom flow diversion ratios of 1.0%, 10.0% and 25.0% were designed. Samples for overflow and bottom flow in 3 different working conditions were taken, and inlet flow, inlet concentration, bottom flow, bottom concentration, and concentration of overflow were measured so as to calculate the separation efficiency. The separation efficiency from the numerical simulation was compared with that obtained from the experiment. The results showed the relative error of the separation efficiency obtained from simulation and experiment was within 10%, indicating that the numerical simulation method was reliable. The separation efficiency was increased gradually with increasing inlet pressure, further verifying the feasibility of numerical simulation. At the inlet pressure was less than 0.3 MPa, the simulated data was consistent with the measured data on the working condition 1 (diversion ratio was 1.0%), but the former was less than the latter on the working condition 2, and 3 (diversion ratio was 10.0% and 25.0%). At the inlet pressure was greater than 0.3 MPa, the simulated result was greater than the measured result on the three different working condition. On the basis of the experiment, this paper analyzed the speed distribution, turbulent kinetic energy distribution and static pressure distribution of the centrifugal separator by applying computational fluid dynamics (CFD) software with the high-silt content water as micro-irrigation water source in water shortage areas. The results showed that velocity in centrifugal separator was distributed along the tangential, axial and radial directions, and the velocity distribution had symmetry along the radial direction. The turbulent kinetic energy of the centrifugal separator had symmetry, and the distribution from the middle to the wall on both sides became gradually smaller. The static pressure distribution of the centrifugal separator had symmetry, and the distribution from the wall on both sides to the middle became gradually smaller. The results provide data support for optimization of parameters for centrifugal separator in microirrigation.