Spatiotemporal cavitation dynamics in submerged cavitating jets: Influence of standoff distance

Submerged cavitating jets exert significant erosive effects on materials, with non-dimensional standoff distance (NSD) playing a critical role in determining the intensity of erosion. However, the mechanisms through which NSD influences the erosive performance of cavitating jets remain insufficiently understood. This study investigates the complex processes of cavitation cloud evolution, collapse energy transfer, and impingement mode transitions under varying NSDs. Stress-blended eddy simulation turbulence model is employed in numerical simulations, combined with erosion experiments, to analyze the erosion characteristics of cavitating jets across different NSDs. Additionally, spectral proper orthogonal decomposition (SPOD) is applied to examine the spatial distribution and coherent structures of cavitation clouds. The results demonstrate the existence of an optimal NSD at which the cavitation cloud reaches its maximum thickness. At this optimal NSD, the larger impinging cloud is primarily sustained by entrained expanding vapor from the jet core in the free-flow region. As NSD increases, high-amplitude impingement events become more pronounced, and the prolonged lifespan of cavitation clouds intensifies their collapse and erosion effects. SPOD analysis further reveals a shift in cavitation fluctuation energy toward lower frequencies, indicating that larger NSDs promote the formation of large-scale clouds. Moreover, impinging clouds formed at the optimal NSD exhibit synchronized collapse behavior and greater fluctuation energy.