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

针对雾化喷嘴孔口形成的中空锥形液膜，研究了中空锥形喷雾中液滴和气流的行为。用脉冲激光对液膜进行拍照，观察液膜的形状。用相位多普勒法检测液膜破碎点附近液滴的行为。进行了数值模拟，将实验结果与预测结果进行了比较。结果表明：(1)雾化孔处形成的液膜锥角随流量增大而趋于收敛或减小。瞬时夹角小于观测到的液膜时间平均包络的夹角。破碎点处液膜的流动方向决定了液滴的初始速度及其方向。液膜的形状与液膜的表面张力有关。(2)液膜的破碎点起伏不定，液滴的初始速度和方向波动很大。(3)考虑液膜的存在，数值模拟表明液膜的运动诱导了强烈的气流，这种气流选择性地输送小液滴，并对液滴的大小和分散程度进行分类。

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.