Motion and dispersion of small particles in a turbulent free shear flow and its control

利用激光多普勒仪对同向流动湍流射流中小颗粒的运动进行了实验研究。从收缩比分别为1.0、1.44、3.24和7.84的四种不同喷嘴排出含有稀薄颗粒的空气。测量了0.8微米DOP气溶胶、32微米玻璃微珠、58微米玻璃微珠和100微米玻璃微珠四种不同粒径颗粒的平均速度、脉动、流动角和浓度。结果表明，喷嘴收缩比对喷嘴出口颗粒速度有很大影响，这种变化对较大颗粒(玻璃微珠)在射流中的速度和浓度有显著影响。四种不同喷嘴的颗粒在射流中的流动角度相同，但较大颗粒的偏转角大于DOP颗粒，这与射流的大尺度旋涡结构有关，并讨论了通过颗粒初始速度变化来控制颗粒扩散的可能性。

The motion of small particles in a coflowing turbulent jet is investigated experimentally by means of a laser Doppler anemometer. The air with dilute particles is issued from four different nozzle of which contraction ratio is 1.0, 1.44, 3.24 and 7.84. Average velocity, fluctuation, flow angle and concentration of particles are measured to clarify the effect of nozzle contraction for four different size of particles of 0.8mum DOP aerosols, 32mum glass beads, 58mum glass beads and 100mum glass beads.The results indicate that particle velocity at nozzle exit is changed strongly by nozzle contraction ratio, and this change exerts a marked influence on the velocity and the concentration of larger particles (glass beads) in the jet. The phenomenon that the flow angles of particles in the jet are same for four different nozzle but larger particles have large deflection angle than that of DOP particles is attributed to the large scale vortex structure of the jet.The possibility of the control of particle dispersion by means of particle initial velocity change is also discussed.