The interaction of an air bubble (isolated in water or attached to a boundary) with shock waves induced by electric sparks is investigated by high-speed photography.The interaction is closely related to the counter-jet induced by the impact of shock waves.The formation of a counter-jet in an air bubble is related to the liquid jet formed in the same air bubble,but the mechanism is different with that of the counter-jet formation in a collapsing cavitation bubble.The formation of a counter-jet in an air bubble is related to discharge energy,air bubble size and radius of shock wave.With a given energy of the spark discharge,the formation of a counter-jet in an air bubble is related to δ /ε (the ratio of the dimensionless bubble-bubble distance to the dimensionless air bubble radius).The counter-jet will only be produced when δ /ε is in the range of 1.2-2.2.The counter-jet in an air bubble is of an important nuclei-generating mechanism.
