When a cavitation bubble collapses, it forces energetic liquid into a very small volume, thereby creating a spot of high pressure and emitting shock waves. A highly localized near-wall collapse can generate a liquid jet and erode metals, such as steel, over time. In devices such as propellers, this cavitation process causes damage to components and a loss of efficiency. Previous studies have been extensively focused on the impact of the jet and shock emission.
In our recent experiment of the interaction of a 2mm tantalum block with underwater explosion, the TA cubic block is accelerated neither by the shock wave nor the jet. Instead, it moves towards the explosion center, in the opposite direction of shock wave propagation and jet impact. This unexpected result initiates us to investigate the collapsing of a near-wall bubble more thoroughly with a focus on the formation of suction force. In fact, industrial cleaning applications using ultrasound indicates that the cavitation has also a sufficient power to overcome the particle-to-substrate adhesion forces. This fact also implies the existence of a suction force exerting on the wall surface during the collapse of a near-wall bubble.
In this paper, the collapsing of a near-wall bubble is investigated using a fully compressible two-phase model. Special attention is paid to the suction force. It is found that the bubble collapse generate a pressure lower than the ambient one on the wall surface, as well as a much stronger pressure rise due to the jet impact. However, the average of pressure on the wall over long time can be lower than the ambient pressure, or the bubble collapse actually generates a suction force during the whole collapsing process.
