AI 中文总结
研究气体聚焦微射流速度快的原因，用确定性动力学求解器解析聚焦气体膨胀并与液体射流耦合，发现射流是剪切驱动，由单一稀疏参数及热力学德博拉数确定气体本构状态，为非牛顿计算提供应力输入。
AI 中文摘要
气体聚焦液体微射流是串行飞秒晶体学所依赖的流聚焦样品输送方式，其速度比压力驱动（伯努利）极限快几倍，连续、局部平衡模型无法解释，因为这些模型未解析聚焦气体的稀薄、高超音速膨胀。我们用确定性动力学（Shakhov - BGK）求解器解析这种膨胀，并将其与细长液体射流耦合。射流是剪切驱动而非压力驱动，高超音速气体的切向应力提供了几乎所有轴向动量，解释了异常速度。气体在近场之后不会变成弹道式，其应力按幂律衰减且保持耦合，其本构状态由单一稀疏参数\(\delta = D / \ell_0\)（孔口直径与源平均自由程之比）通过热力学德博拉数\(De_\theta \simeq Kn\,M\)（克努森数乘以马赫数）确定，\(De_\theta = 1\)的表面描绘了牛顿气体封闭失效的位置：晶体学射流运行的小\(\delta\)真空区域。动力学计算的表面应力是完全非牛顿（粘弹性液体）后续计算的输入。
英文摘要
Gas-focused liquid microjets -- the flow-focusing sample delivery on which serial femtosecond crystallography depends -- reach speeds several times the pressure-driven (Bernoulli) bound, unexplained by continuum, local-equilibrium models that do not resolve the rarefied, hypersonic expansion of the focusing gas. We resolve that expansion with a deterministic kinetic (Shakhov--BGK) solver and couple it to the slender liquid jet. The jet is \emph{shear-driven}, not pressure-driven: the tangential stress of the hypersonic gas supplies nearly all of the axial momentum, accounting for the anomalous speed. The gas does not become ballistic behind the near field -- its stress decays as a power law and it stays coupled -- and its constitutive regime is set by a single rarefaction parameter $δ=D/\ell_0$, the orifice diameter over the source mean free path, through the thermodynamic Deborah number $De_θ\simeq K\!n\,M$ (Knudsen times Mach), whose $De_θ=1$ surface maps where the Newtonian-gas closure fails: the small-$δ$ vacuum corner where crystallography jets operate. The kinetically computed surface stress is the input for the fully non-Newtonian (viscoelastic-liquid) sequel.
Comments6 pages, 5 figures (18 plots)
