I do not see the problem: there where the gas in contact with the fluid jet the static pressure in the jet has to be lower than the static pressure of the gas.

Due to the low gas viscosity the shear stresses are of lower effect. But you also use them if the gas envelope has a small angle to the jet profile and generates a kind of wedge. The distance between jet surface and eveloppe decreasing the shear stress proportional to the velocity gradient increases.

See the attached link.

https://www.bamfordandmorris.com/operation.html

https://www.sciencedirect.com/search?qs=jacketed%20ejector%20cooled%20by%20cooling%20water&show=25&sortBy=relevance