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

用激光多普勒测速仪对同向湍流射流中小颗粒的运动进行了实验研究。稀释颗粒空气由四个不同的喷嘴喷出，收缩比分别为1.0、1.44、3.24和7.84。通过测量0.8 μ m DOP气溶胶、32 μ m玻璃珠、58 μ m玻璃珠和100 μ m玻璃珠四种不同粒径气溶胶的平均速度、脉动、流动角和浓度，研究了喷嘴收缩对气溶胶颗粒出口速度的影响，结果表明：喷嘴收缩比对颗粒出口速度的影响很大，并且这种变化对射流中较大颗粒（玻璃珠）的速度和浓度产生显著影响。四种喷嘴中颗粒的流动角相同，但大颗粒的偏转角比DOP颗粒的大，这是由于射流中存在大尺度的旋涡结构，并讨论了通过改变颗粒初速度来控制颗粒弥散的可能性。

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.