强迫扰动下的射流撞击雾化特性

为全面把握撞击式喷嘴的工作特性，进一步认识雾化在燃烧不稳定中所起的作用，采用试验结合数值模拟的方法开展了强迫扰动条件下撞击式喷嘴的非稳态雾化特性研究。试验方面，采用水力扰动装置产生喷前压力扰动，由脉动压力传感器记录喷前的脉动压力，由高速摄影对动态的喷雾场进行背光拍摄。数值模拟则是基于开源程序Gerris开展，通过给定周期性变化的速度入口来模拟前端压力扰动下的撞击雾化过程。首先验证了建立的数值模拟方案处理非稳态雾化的有效性，其次将自然雾化与强迫扰动雾化进行对比，分析了强迫扰动条件下的撞击雾化特性，最后研究了扰动频率与扰动幅值对于撞击雾化的影响。结果表明：强迫扰动下的射流撞击喷雾场出现了弓形液滴群局部聚集的现象，并且在时间上表现出周期性特征，雾化频率与强迫扰动的频率一致。在研究的频率范围（1 257~3 563 Hz）内，撞击式喷嘴的雾化对扰动都有响应。扰动频率主要影响相邻弓形液滴群之间的间距以及雾场与扰动压力之间的相位关系，扰动幅值则主要影响雾化Klystron效应的强度。随着扰动幅值的增大，液膜的破碎长度减小，撞击点下游的流量特性由线性向非线性转变，由正弦波形转变为陡峭前缘波形。

Atomization characteristics of impinging liquid jets coupled with forced perturbation

To comprehensively grasp the working characteristics of impinging jet injectors and further understand the role atomization plays in combustion instability, the unsteady atomization characteristics of impinging jet injectors coupled with forced perturbation are investigated experimentally and computationally. For the experiment, pressure perturbations in the feed pipe are generated by a hydro-mechanical pulsator, pressure fluctuations are recorded by pulsating pressure transducers, and backlit images of dynamic atomization field are captured by high-speed camera. For the simulation, based on open-source software Gerris, atomization processes coupled with forced perturbations are simulated by setting a periodically varying velocity inlet. The ability of the established numerical schemes to simulate the unsteady atomization process is first validated. Secondly, the natural atomization process is compared with forced atomization, and the atomization characteristics of impinging liquid jets coupled with forced perturbations are analyzed. Finally, the effects of perturbation frequency and amplitude on impinging jet atomization are investigated. Results revealed that for impinging jet atomization coupled with forced perturbations, arc-shaped groups of droplets accumulate in the atomization field which exhibits periodical characteristics. The frequency of atomization is consistent with that of forced perturbations. Within the frequency range (1 257-3 563 Hz) in this study, the atomization process always responds to pressure perturbations. The perturbation frequency mainly affects the distance between adjacent arc-shaped droplet groups and the phase relation between atomization field and oscillating pressure field, while the perturbation amplitude mainly affects the strength of Klystron effect. With the amplitude increasing, the breakup length of the liquid sheet decreases, and the mass flow rate downstream of the impingement point changes from linear pattern to non-linear one, that is, from sinusoidal waves to steep-fronted waves.