This paper uses a combination of numerical and theoretical techniques to evaluate dynamical threshold for cavitation in water triggered by weak tension. Within the test section of a once-through, nonrecirculating cavitation tunnel, a cylinder is installed, behind which cavitation occurs, and once cavitated, water cannot return to the monitoring section. The single-phase water flow has been simulated using an LES-based CFD solver to observe velocity distribution at the throat, pressure distributions before and after the throat, flow separation, and vortex formation downstream of the separation point. Bubble dynamics analysis using the Rayleigh-Plesset equation is conducted for conditions under which bubble nuclei supposed to exist in water grow according to CFD-based pressure histories and along streamlines, revealing that nuclei with O(1 μm)-radius suddenly start growing beyond the throat, largely depending on the streamlines. Finally, dynamical cavitation threshold theory is successfully applied to predict nuclei growth, resulting in rather good agreement with the bubble dynamics analysis.

Theory of dynamical cavitation threshold for vapor and non-condensable gas bubble nuclei is proposed based on a model equation constructed from Rayleigh-Plesset equation for glycerol, the liquid with viscosity higher than that of water by 1500 times, under a finite duration of strong tension. The model equation is ascertained to be valid in cases of strong tension under which cavitation occurs. Our model enables the study of dynamics of nuclei on the phase plane of the nucleus radius and the growth velocity, by which the full details of the threshold are revealed. We propose a dimensionless parameter to be used to classify the threshold of cavitation. Our model offers a simple mathematical expression to calculate the maximum radii attained, while under tension, for each of these three recognized patterns. For each observed pattern, we present unique predictive correlations for the radius of the nucleus growing for the tension duration. Moreover, we elucidate that the dynamics of the nuclei, grown up to certain sizes, is fully controlled by tension independent of the viscosity. The discrepancy between the dynamical threshold and the conventional Blake’s threshold is discussed. Finally, the utility of the theory presented here is demonstrated through numerical examples.