Elucidation of the gas flow and droplet behavior near the liquid sheet at the nozzle exit of the hollow-cone spray

研究了空锥喷雾中液滴和空气的流动行为，注意到空锥喷雾喷嘴孔处形成的空锥液膜。用Nd-YAG脉冲激光器对液片进行了照相，研究了液片的形状。采用相位多普勒法对液膜破裂点附近液滴的运动进行了测量。数值模拟进行了比较实验的预测。所得结果如下。(1)在雾化器孔处形成的液体层的锥角趋于随着流动而沿着或减小。瞬时角度小于所观察到的液膜的时间平均包络。液膜在破碎点处的流动方向决定了液滴的初始速度和方向。形状与液体片的表面张力有关。(2)液膜破裂点上下波动，液滴初始速度和方向波动较大。(3)数值模拟结果表明，液膜的运动引起了强烈的气流，气流选择性地输送小液滴，并对液滴的大小和分散性起着重要的作用。

Behavior of droplets and the air flow in a hollow-cone spray was studied paying atteintion to the hollow-cone liquid sheet formed at the atomizer orifice. The shape of the liqiud sheet was investigated by taking photographs with a flush of Nd-YAG pulse laser. Phase Doppler method was used to detect the behavior of the droplets adjacent to the break-up point of the liquid sheet. Numerical simulation was carried out to compare the experiments to the predictions. The results obtained are as follows.(1) The cone angle of the liquid sheet formed at the atomizer orifice tends to converge or decrease along with the flow. The instantaneous angle is less than that of the observed time-averaged envelop of the liquid sheet. The direction of the liquid sheet flow at the break-up point dominates the initial droplet velocity and its direction. The shape is related to the surface tension of the liquid sheet.(2) The break-up point of the liquid sheet fluctuates up and down and the initial droplet velocity and the direction fluctuates significantly.(3) Numerical simulation incorporating the existence of the liquid sheet reveals that the the movement of the liquid sheet induces strong air stream and that this air stream selectively transports small droplets and plays an essintial role in classification of droplets by size and dispersion of droplets.