双进气道柴油机丝线法可视化稳流测试及缸内气流运动特性分析

Steady Airflow Test and In-cylinder Flow Motion Analysis of Double Inlet-channel Diesel Engine Based on Tuft Flow Visualization

搭建基于丝线法的发动机可视化气道稳流实验台,对气缸内近壁面流场进行可视化研究,同时利用CFD对气缸内近壁面气流运动进行了数值模拟,并将实验结果与模拟结果进行相互验证。结果表明:在稳流条件下,气缸壁面的丝线运动可直观体现缸内近壁面气流运动情况。气缸近壁面丝线运动方向受到螺旋气道产生的涡流作用,使丝线运动方向与涡流方向一致。切向气道侧近壁面流场在切向气道内气流和涡流运动的共同作用下,其气流速度最大,相应地此处的丝线摆动角度也最大。气门升程为8和12mm时,丝线摆动角度分别为110°和90°。缸内瞬态流场存在涡流和滚流运动,但很快合并成单一的涡流运动。

A visualized test bed for the steady flow in engine air-passage is built based on tuft method to conduct visualized study on the flow field near cylinder wall, and meanwhile a numerical simulation on the same object is also performed using CFD technique, with both results verified each other. The results show that under steady flow conditions, the tuft motion can intuitively reflect the airflow movement near cylinder wall. Due to the effects of vortex generated by spiral air-passage, the moving direction of tuft is consistent with that of vortex. As for the flow field near cylinder wall at tangential air-passage side, its flow velocity reaches the maximum due to the co-action of the air-flow in tangential air-passage and the vortex motion, and accordingly the swing angle of tuft there also reaches its peak value. They are 110° and 90° for 8 and 12 mm valve lift respectively. In-cylinder transient flow field has both vortex and tumble motions, but they quickly merged into a single vortex motion.