Aeroacoustic resonance in particle-laden impinging jets

Supersonic impinging jets exhibit a self-sustaining aeroacoustic feedback loop between downstream convecting hydrodynamic disturbances and upstream-traveling acoustic waves. This resonance generates intense tones, shock oscillations, and large-amplitude pressure fluctuations in the impingement region. Although these mechanisms are well documented for single-phase jets, their behavior in particle-laden impinging jets remain poorly understood, despite the relevance to systems such as cold-spray deposition nozzles and solid-rocket exhausts where particle loading and supersonic resonance directly affect performance efficiency. This thesis investigates how solid particles alter the resonance cycle and how the resulting unsteadiness modifies particle trajectories and deposition behavior. A sequence of large-eddy simulations (LES) is performed beginning with canonical single-phase impinging jets and progressing to fully coupled particle-laden configurations. The jets are studied first from a straight pipe nozzle and then from a long-diverging, cold-spray-style nozzle representative of industrial systems. Two particle-coupling modes were evaluated: a one-way-coupled case (Jet C), in which particles respond to the flow without feedback, and a two-way-coupled case (Jet D), in which momentum exchange modifies the carrier phase. To resolve the upstream and downstream components of the resonance cycle, Doak’s Momentum Potential Theory (MPT) is applied to decompose the momentum field into hydrodynamic, acoustic, and thermal components, enabling isolation of acoustic sources from turbulent fluctuations. The single-phase simulations reveal two resonance-generation mechanisms: (1) a tail-separation mechanism in which vortices detach the trailing edge of the bow shock, and (2) a higher-frequency lambda-shock mechanism near the jet core, where successive vortices compress the bow shock. Both of these mechanisms generate upward propagating acoustic waves. Together these mechanisms define the spectral structure of the dominant tone. When particles are introduced, the resonance topology persists, but the feedback loop accelerates, increasing the dominant tone frequency. Two-way coupling enhances small-scale turbulence and strengthens vortex–shock interactions. The resulting unsteadiness governs particle deposition. One-way coupling produces the largest dispersion in the outer shear layer, whereas two-way coupling yields the greatest spreading near the jet centerline. These findings show that resonance-driven fluctuations, not mean flow fields, control particle trajectories, offering a physical explanation for reduced deposition efficiency in high-speed cold-spray systems.