离心喷嘴脉冲工作动态特性实验研究

Experimental Study on Dynamic Characteristics of Swirl Injector Working in Pulse Mode

关键词:  双组元推力器  离心喷嘴  脉冲喷雾  索太尔平均直径  液膜锥角

Key words:  Bipropellant thruster  Swirl injector  Pulse spray  Sauter mean diameter  Spray cone angle

摘要:

双组元推力器在短脉冲工况下比冲出现明显下降。为了从推进剂雾化角度研究其原因，搭建了离心喷嘴脉冲工作冷流实验平台，使用机械式脉动流量发生器使喷嘴工作在脉冲模式。实验中测量了离心喷嘴的动态压降和索太尔平均直径SMD随时间的振荡，并使用高速相机拍摄了喷雾场和喷嘴内部流动的瞬时照片。通过提取图像边界的方法测量了液膜锥角的变化，并计算了一个周期内不同大小SMD时间占比分布。瞬时照片和SMD的测量结果表明，脉冲工作的离心喷嘴在脉冲工作时会出现柱状射流或由调速管效应形成的厚液环，导致喷雾场出现较大液滴。喷雾锥角测量结果表明，脉冲结束后液膜并不随着压降下降而直接收缩，而是继续保持较大锥角一定时间。对SMD的分析表明，脉冲宽度越小，一个脉冲内非稳态喷雾时间占比越大，导致整个脉冲的雾化质量越差。根据本文研究结果，为了提高离心喷嘴窄脉宽工作时的雾化性能，需要尽可能消除柱状射流和调速管效应的影响。

Abstract:

The specific impulse of the bipropellant thruster decreases significantly under short pulse conditions. In order to find out the reason from the perspective of propellant atomization， a cold flow test platform for pulsed working swirl injectors was set up， and a hydrodynamic mechanical pulsator was used to make the injector work in pulse mode. The dynamic pressure drop of the swirl injector and the oscillation of the Sauter mean diameter （SMD） over time were measured. Transient images of the spray field and the flow inside the injector were captured by a high-speed camera. The oscillation of the spray cone angle was measured by the method of extracting the image boundaries， and the time proportion distribution of different SMD values over a period was calculated. Transient images and SMD measurement results show that columnar jet or thick liquid ring formed by the Klystron effect will appear during pulse working conditions for the swirl injector， resulting in larger droplets in the spray field. The measurement results of spray cone angle show that the liquid sheet does not shrink directly with the drop of the pressure， but keeps a large angle for a certain time. The analysis of SMD shows that the smaller the pulse width is， the greater the proportions of unsteady spray time in a pulse， resulting in a worse atomization quality. According to the research results of this paper， in order to improve the atomization performance of the swirl injectors at narrow pulse width， it is necessary to eliminate the influence of columnar jet and the Klystron effect.