[en] The interaction of a coherent liquid jet with a free supersonic gas jet is of importance in cooling high-temperature exhaust plumes generated by ground rocket tests. Further, the associated phenomena are distinct from the well-studied jet in supersonic crossflow due to the unbounded nature of the gas jet, its shock train structure, and the relative sizes of the two jets. This work utilizes non-intrusive diagnostics including focused color Schlieren, high-speed diffused backlit imaging, and volume-illuminated imaging to study the interaction process of a high Reynolds number water jet with a free supersonic air jet. The effect of the water jet on the shock train structure and its dependence on water injection location and pressure are studied. The ensuing water jet breakup mode is investigated and found to exhibit distinguishing characteristics from known breakup modes observed at high Reynolds and gas Weber numbers. Finally, the water jet penetration height is quantified, and the ability of existing correlations from the literature to predict the penetration height are investigated. Graphic abstract:

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