微灌鱼雷网式过滤器全流场数值模拟

Numerical simulation on flow field of screen filter with torpedo in micro-irrigation

为了充分了解鱼雷网式过滤器内部流场分布规律,该文应用雷诺时均(Reynolds-Averaged Navier-Stokes,RANS)方程及RNG k-ε湍流模型,对过滤器内部全流场进行全流场数值模拟。结果表明:鱼雷部件和出水口边界条件对该过滤器的速度流场和压力场分布规律影响很大,鱼雷部件的影响是尤为突出;滤网及其内、外侧的水流流速沿X轴的变化规律分流速迅速增加、流速迅速减小和流速缓慢减小3个阶段;滤网内外压力分布有很大的的差异,滤网内侧压力沿X轴分布从迅速增加到缓慢减小、最后趋于稳定。而滤网外侧压力分布沿X轴的变化很大,特别是在出水口处压力迅速减少,压力沿X轴的波动幅度较大。滤网内侧压力比外侧的大,两者的压力差沿X轴越来越小,最大压力差为23 k Pa左右,最小压力差为0.5 k Pa。研究结果认为整个滤网堵塞不均匀,滤网堵塞呈现从尾部开始向出水口方向发展的趋势,对后续滤网的冲洗排污产生重要影响。该文建议在设定最佳排污压差时需要慎重考虑。

In order to deeply understand the flow distribution of the torpedo screen filter, the Reynolds-averaged Navier-Stokes（RANS） equation and Re-Normalization Group （RNG） k-e turbulence closure model were used to simulate the flow field ofthis filter system. To ensure the reliability of the numerical simulation, the physical experiment results were compared to thenumerical simulation results, and the result showed that the maximum relative error between the head loss in the physicalexperiment and the numerical simulation was 5.99% when the filtering system was operated at a maximum flow rate of 360m/h, indicating reliability of the simulation method. The simulation results showed that the torpedo components and theboundary conditions of the outlet notably affected the distribution rules of both the velocity and the pressure fields for the filter,especially for the torpedo components. The distributions of the flow velocities of inside and outside of the screen along theX-axis were not uniform during the filtering process. And the flow velocity distributions inside and outside of the filter screenalong the X-axis were divided into 3 stages： 1） a rapid increase; 2） a rapid decrease; and 3） a gradual decrease. The maximumvelocities inside and outside of the screen and their spatial locations along the X-axis were different. For the upper part of thescreen, the inside flow velocity increased in a larger amplitude than did the outside flow velocity, and the flow velocityachieved its maximum （5.53 m/s） at the X value of 0.29 m. The outside water flow velocity of the upper part of the screenachieved its maximum value （3.9 m/s） at the Xvalue of 0.33 m. When the Xvalue ranged from 0.2 to 0.6 m, the inside flowvelocity of the upper part of the screen was larger than that of the outside; however, the difference in the flow velocity alongthe X-axis continually decreased from the maximum difference of 4.1 m/s. For the lower part of the screen, the maximum flowvelocity and its position of lower part of the screen was 5.4 m/s and 0.42 m, respectively. When the X value was 0.41-0.51 m,the flow velocity of the water in the outside area of the lower part of the screen was larger than that of water in the inside area.Nonetheless, the flow velocities of water in the other inside of lower screen were higher than those of water in the outside, andthe maximum difference in the flow velocity was 2.28 m/s. There was a notable difference in the pressure distributions alongthe inside and outside of the screen. The pressure of the inside along the X-axis first rapidly increased, then graduallydecreased, and finally stabilized. In contrast, the pressure of the outside along the X-axis exhibited a greater variation; forexample, the pressure rapidly decreases at the outlet, and the fluctuations along the X-axis are relatively large. The pressure ofthe inside of the screen was larger than that of the outside; however, the pressure differences along the X-axis continuallydecreased, and the maximum and minimum pressure differences between the two were approximately 23 and 0.5 kPa,respectively. This indicated that the screen clogging was not evenly distributed, and the screen clogging began at thedownstream end of the screen and developed progressively upstream towards the outlet. This phenomenon significantlyaffected the cleaning process of the filter. Therefore, it is strongly suggested that in a practical application the optimumdrainage differential pressure must be circumspectly considered.