射流自由长度对凝胶推进剂撞击雾化影响的实验

为研究射流自由长度对凝胶推进剂撞击雾化的影响,建立了撞击雾化实验台,制备了煤油凝胶和水基模拟液,测试了雾化装置的喷射系数及模拟液的黏性和稳定性。分析了3种射流速度不同射流自由长度条件下的凝胶撞击雾化特性,观测了射流和撞击喷雾图像。测量了液膜破碎长度、雾化液滴粒径分布和相应的SMD(索太尔平均直径)值。研究结果表明:低速时,随着射流自由长度增大,撞击液膜的喷雾形态会发生较大变化,而高速条件下,雾化形态则基本一致。3种射流速度下,破碎长度在45~9mm之间,并随射流自由长度逐渐减小。液滴分布服从Rosin Rammler规律,并具有较高的拟合精度。均匀度指数均在3~4之间,并随射流自由长度逐渐降低,粒径均匀度降低；较高射流速度下,SMD随自由长度逐渐增大。低射流速度时，SMD随射流长度先减小后增大,射流自由长度存在一个最优值,在设定研究条件下其值为25/3。因此,在设计撞击喷嘴时,根据射流速度选取适当的自由长度值可以获得更好的雾化效果。 

Experiment on effect of free jet length on impinging atomization of gel propellant

In order to study the effect of free jet length on impinging atomization of gel propellant, an impinging atomizer was designed, and gelled kerosene and corresponding water based simulant were prepared. Discharge coefficient of the injector and the viscosity and stability of the simulant were measured. Impinging atomization experiments were conducted under different free jet lengths for three jet velocities. Spray behavior of the jet and impinging sheet was observed. The breakup length, droplet distribution and SMD(Sauter mean diameter) were obtained. Relative results indicated that increasing free jet length resulted in great change of spray behavior of impinging sheet when jet velocity was low. But spray behavior nearly kept the same at high jet velocity. For three jet velocities, breakup length located between 45mm and 9mm, and decreased with the free jet length. Droplet distribution was in accordance with Rosin Rammler relation with a high fitting accuracy. All the evenness indexes were between 3 and 4, and gradually declined with the free jet length implying a reduced evenness of droplet diameter. SMD increased with the free jet length at higher jet velocity. In the case of lower jet velocity, SMD decreased at first and then increased slowly. There is an optimal value for free jet length, and the value equals to 25/3 at present. As a result, when designing an impinging injector, better atomization quality can be reached by applying an optimal free jet length.