Study on the transient characteristics of pulsation bubble near a free surface based on finite volume method and front tracking method

Abstract

The pulsation bubble dynamics near a free surface have significant engineering applications. Based on the finite volume method, a front tracking method coupled with an extrapolation technique is applied to study the transient characteristics of the pulsation bubble near the free surface with the different stand-off distance parameter γ and buoyancy parameter δ (the parameters are defined in Sec. II D). By comparison, the numerical results agree well with the results from the spark-generated bubble experiment. For the cases with small δ, (i) the phenomenon that the bubble top is elongated is no longer obvious while γ > 2.0, (ii) with the decrease in γ, the bubble centroid at the minimum volume is gradually away from the free surface except for migrating upward while 0.85 < γ < 1.0, and (iii) while γ > 1.2, the free surface begins to fall with the bubble collapse after rising during the expansion stage and almost falls back to its original position while γ > 2.4. For the cases with γ = 1.0–1.13, (i) while δ > 0.2293, the jet penetrates the bubble before the bubble reaches its minimum volume, and both are contrary while δ < 0.2293, (ii) while δ > 0.4636, the free surface begins to fall with the bubble collapse after rising during the expansion stage, and (iii) the bubble is always migrating toward the free surface while δ > 0.4109. Meanwhile, the phenomena such as the inward jet formed inside the toroidal bubble, the toroidal bubble split, and the water skirt are also analyzed.