Impinging gas jets can induce depressions in liquid surfaces, a phenomenon familiar to anyone who has observed the cavity produced by blowing air through a straw directly above a cup of juice. A dimple-like stable cavity on a liquid surface forms owing to the balance of forces among the gas jet impingement, gravity and surface tension^1,2. With increasing gas jet speed, the cavity becomes unstable and shows oscillatory motion, bubbling (Rayleigh instability) and splashing (Kelvin–Helmholtz instability)^3,4. However, despite its scientific and practical importance—particularly in regard to reducing cavity instability growth in certain gas-blown systems—little attention has been given to the hydrodynamic stability of a cavity in such gas–liquid systems so far. Here we demonstrate the stabilization of such instabilities by weakly ionized gas for the case of a gas jet impinging on water, based on shadowgraph experiments and computational two-phase fluid and plasma modelling. We focus on the interfacial dynamics relevant to electrohydrodynamic (EHD) gas flow, so-called electric wind, which is induced by the momentum transfer from accelerated charged particles to neutral gas under an electric field. A weakly ionized gas jet consisting of periodic pulsed ionization waves⁵, called plasma bullets, exerts more force via electrohydrodynamic flow on the water surface than a neutral gas jet alone, resulting in cavity expansion without destabilization. Furthermore, both the bidirectional electrohydrodynamic gas flow and electric field parallel to the gas–water interface produced by plasma interacting ‘in the cavity’ render the surface more stable. This case study demonstrates the dynamics of liquids subjected to a plasma-induced force, offering insights into physical processes and revealing an interdependence between weakly ionized gases and deformable dielectric matter, including plasma–liquid systems.

撞击的气体射流会导致液体表面出现凹陷，这种现象对于任何观察过通过直接在一杯果汁上方的吸管吹气而产生的空腔的人来说都是熟悉的。由于气体射流冲击、重力和表面张力^1,2之间的力平衡，液体表面上形成了一个类似酒窝的稳定空腔。随着气体喷射速度的增加，空腔变得不稳定并显示出振荡运动、冒泡（瑞利不稳定性）和飞溅（开尔文-亥姆霍兹不稳定性）^3,4. 然而，尽管它在科学和实际方面具有重要意义——特别是在减少某些吹气系统中的空腔不稳定性增长方面——迄今为止，人们很少关注此类气液系统中空腔的流体动力学稳定性。在这里，我们基于阴影图实验和计算两相流体和等离子体建模，证明了在气体射流撞击水的情况下，弱电离气体对这种不稳定性的稳定性。我们专注于与电流体动力学 (EHD) 气流相关的界面动力学，即所谓的电风，它是由电场下从加速带电粒子到中性气体的动量转移引起的。由周期性脉冲电离波组成的弱电离气体射流⁵，称为等离子子弹，通过电流体动力流在水面上施加比单独的中性气体射流更大的力，导致空腔膨胀而不会不稳定。此外，双向电流体动力气流和平行于由“腔内”等离子体相互作用产生的气水界面的电场都使表面更加稳定。本案例研究展示了受到等离子体诱导力的液体动力学，提供了对物理过程的见解，并揭示了弱电离气体和可变形介电物质（包括等离子体-液体系统）之间的相互依赖性。