Attached cavitation is likely the most common form of developed hydrodynamic cavitation, yet the reason for its dominance remains unclear. From the experimental side, a natural approach is to seed controllable nuclei and observe their evolution. We propose a laser-based on-demand nucleation method that generates micro- and nanobubbles as nuclei in Venturi flows, enabling unprecedented spatio-temporal control of hydrodynamic cavitation inception. For single-bubble cases, we find that attached cavitation occurs when the bubble surface enters the boundary layer of the channel where the pressure is below the vapour pressure. Based on it, we construct a phase diagram of cavitation regimes as a function of cavitation number and non-dimensional wall distance. Extending to multiple bubbles, assuming a random spatial distribution of nuclei within the laser-illuminated region, we develop a simple model to estimate the probability of attached cavitation. Results show that, at typical cavitation numbers, only a few bubbles suffice for attached cavitation to occur with nearly 100 % probability. Our finding provides new insights into why nuclei in hydrodynamic processes tend to develop into attached cavitation.
Li et al. (2026) studied this question.