文丘里施肥器空化特性数值模拟

采用数值模拟的方法对结构优化后的文丘里施肥器进行空化特性研究,探讨了空化影响施肥器性能的原因,揭示了施肥器内部流动耗能机理.研究结果表明:随着施肥器进出口压差不断增大,吸肥口负压值不断降低,吸肥流量不断增大,当吸肥口负压降低到最低值时,吸肥口负压值保持不变,吸肥流量将保持恒定,此后随着施肥器进出口压差不断增大,首先在喉部与扩散段连接处产生空化,并沿扩散段壁面向下游不断扩大增厚.通过比较不同压差条件下,施肥器不同截面的能量特征发现,未发生空化时,随着压差增大,喉部能量损失也增大,约占施肥器总损失的1/2左右;空化发生时,随着压差增大,喉部能量损失保持不变,而扩散段能量损失不断增大,这是由于空化的发展使扩散段流态恶化,空化区域外部及尾部产生大范围的涡,消耗较多能量,大量的无效能量损失使得施肥器吸肥效率急剧下降.

Numerical simulation of cavitation characteristics of Venturi injector

The cavitation characteristics of one post-optimized Venturi injector were investigated by numerical simulation, in order to explore declination in the injection performance caused by cavitation and to reveal the mechanism of energy loss in the flow field of Venturi injector. Results show that when the pressure difference across the Venturi increases, the suction pressure decreases continuously and the suction flow rate rises. Once the suction pressure decreases to the minimum, the suction pressure will keep constant, so does the suction flow rate. Then if the pressure difference is increased further, cavitation will occur in the junction between the throat and the diffuser firstly, and then and expand downstream gradually along the diffuser wall. By contrasting the total hydraulic heads at various cross-sections along the Venturi injector axis at different pressure conditions, the energy loss at the throat increases with increasing pressure difference, but it is about half the total energy. Once the cavitation occurs, the energy loss at the throat will keep constant, while the energy loss across the diffuser will be enlarged. This is because cavitation development can deteriorate the flow condition in the diffuser and produce large-scale vortices around the cavities, which consume even more energy. The increased energy consumption results in a sudden and rapid decrease in the injection efficiency.