Enhancing the Aggressive Strength of a Cavitating Jet and Its Practical Application

Abstract

A cavitating jet is a useful tool for the practical application of cavitation. Cavitation impact arises when bubbles collapse and can be utilized to modify the surfaces of materials as an alternative to shot peening. Peening methods using cavitation impact are called "cavitation peening" or "cavitation shotless peening", as shot is not required. In cavitation peening, cavitation is generated by injecting a high-speed water jet into water, i.e., a cavitating jet. In practical applications, it is very important to maximize the aggressive strength of the jet. In the present paper, in order to do this, the outlet geometry of the nozzle of a cavitating jet was optimized. High-speed observations were carried out to investigate any instability in the jet. The introduction of compressive residual stress into stainless steel was demonstrated to show the effect of cavitation peening. Scaling-and velocity-effects, i.e., the effect of the injection pressure, at the nozzle throat was also examined. It was shown that a large cavitating jet at low injection pressure was more aggressive than a small jet at high injection pressure, for the same power.