不同动力环境下孔间距对双孔射流特性的影响

为研究孔间距对双孔射流运动和稀释特性的影响,采用粒子图像测速技术(PIV)和激光诱导荧光技术(PLIF)分别对静水、横流和波浪环境下双孔射流的速度场和浓度场进行测量,对比分析了孔间距为5倍、10倍和15倍射流孔直径时双孔射流的轴向速度、横断面垂向速度、轨迹线及浓度场分布情况。结果表明:在静水环境下,孔间距较小时双孔射流的轴向速度衰减较单孔射流慢,随着孔间距的增大双孔射流轴向速度衰减的程度逐渐趋近于单孔射流。在横流环境下,随着孔间距的增大,前方射流对后方射流的遮掩作用不断减小,而后方对前方射流的卷吸作用也有所减弱,导致前方射流弯曲程度的增大和后方射流上升高度的降低。在波浪环境下,孔间距较小时,两孔中间存在一个独立的高浓度区;孔间距增大后,浓度等值线逐渐呈"凸"形分布。为降低双孔射流相互作用对射流初始稀释的影响,建议在波浪和横流环境下双孔射流的孔间距不宜小于射流孔直径的10倍。

Influence of jet spacing on dual jets in different environments

In order to study the influence of jet spacing on the hydrodynamic and dilution characteristics of dual jets, the velocity and concentration fields of dual jets were studied in stagnant, crossflow, and wave environments using particle image velocimetry(PIV)and planar laser induced fluorescence(PLIF). The axial and cross-section vertical velocity, jet trajectory, and concentration fields were analyzed when the jet spacing varied between 5D, 10D, and 15D, where D is the inner diameter of the jet nozzle. The results indicate that, in a stagnant environment, the decay of the axial velocity for the dual jets with small jet spacing is slow compared with that of a single jet, while it grows faster with the increase of jet spacing and gradually resembles that of the single jet; in a crossflow environment, the shielding effect and entrainment decrease with larger jet spacing, enhancing the bending and lowering the ascending height of jets; and in wavy conditions, there is a dependent high concentration area in the middle of two jet holes with small jet spacing and contour lines grows to be bulge-shaped with larger jet spacing. To reduce the influence of spacing on initial dilution, it is advised that the jet spacing should be larger than 10D in crossflow and wave environments.