Flow characteristics of a confined jet in a cavity: Flow regimes, vortex dynamics, and scaling

A confined jet in a cavity exhibits complex vortex dynamics and transport behavior governed by geometric confinement and jet inertia. In this study, a single upward jet in a cylindrical cavity is investigated using flow visualization, large-eddy simulation (LES), and unsteady Reynolds-averaged Navier–Stokes (URANS) simulations over a wide range of jet Reynolds numbers and cavity aspect ratios. Three distinct flow regimes are identified and mapped in H/D ∼ Rejet space: (i) head-impact laminar flow, largely insensitive to H/D; (ii) sidewall-oscillatory turbulent flow for H/D 3.0; and (iii) head-impact turbulent flow for 0.6–0.8 ≤ H/D 3.0. Oscillatory behavior originates from asymmetric evolution of large-scale vortex structures, with a hierarchical distribution of turbulent intensity from the jet core to reverse and secondary flows. A cavity-based Reynolds number is introduced to characterize global transport, and the resulting parameter Rebody/Rejet provides a unified description of momentum redistribution across scales. For H/D 2.2, the volumetric flow rate distributions collapse onto a unimodal profile with a peak value of approximately 0.8. For 0.6–0.8 H/D 2.2, the distribution transitions to an M-shaped profile, reflecting the competing contributions of primary and secondary flows. Below this range, the profile reverts to unimodal with a higher peak (1.2), corresponding to the suppressed secondary flow and dominant cavity-scale circulation. These results provide a unified scaling framework linking flow regimes, vortex dynamics, and cavity-scale transport in confined jet-cavity systems.