We study numerically and experimentally the stability of the transonic flow focusing used in serial femtosecond crystallography (SFX) to place complex biochemical species into the beam focus. Both the numerical and experimental results indicate that the minimum flow rate for steady jetting increases slightly with the gas stagnation pressure. There is a remarkable agreement between the stability limit predicted by the global stability analysis and that obtained experimentally. Our simulations show that the steady jetting interruption at the critical flow rate is caused by the growth of a perturbation with a constant phase shift. This result is consistent with the experimental observations, which indicate that both the meniscus tip and the emitted jet collapse almost simultaneously at the stability limit. We derive a scaling law for the jet diameter as a function of the liquid flow rate and gas density/pressure from more than one hundred simulations. The scaling law provides accurate predictions for the jet diameter within the range of values [0.549,10.9] $\mu$m analyzed in this work.

我们通过数值和实验研究了连续飞秒晶体学 (SFX) 中使用的跨音速流动聚焦的稳定性，以将复杂的生化物质置于光束焦点中。数值和实验结果都表明，稳定喷射的最小流量随着气体驻点压力的增加而略有增加。全局稳定性分析预测的稳定性极限与实验获得的稳定性极限之间存在显着的一致性。我们的模拟表明，临界流速下的稳定喷射中断是由具有恒定相移的扰动的增长引起的。该结果与实验观察一致，这表明弯月面尖端和发射的射流几乎同时在稳定极限处坍塌。我们从一百多个模拟中推导出射流直径的标度定律，作为液体流速和气体密度/压力的函数。标度定律在值 [0.549,10.9] 范围内对射流直径提供准确预测$\mu$m 在这项工作中进行了分析。