Temporal–spatial spray characteristics of self-excited sweeping nozzles in crossflow: An experimental investigation

Self-excited sweeping (SES) nozzles have attracted growing interest due to their ability to generate high-frequency oscillating jets. While prior studies have clarified their flow dynamics and atomization under atmospheric conditions, their behavior in crossflow—relevant to aero-engine and afterburner combustors—remains insufficiently understood. This study experimentally investigates the spray characteristics of a SES nozzle operating in a high-speed crossflow, with an emphasis on the influence of injection pressure. A two-dimensional phase Doppler particle analyzer (PDPA) was employed to measure droplet size and velocity distributions at multiple downstream locations. The results show that the spray morphology evolves markedly downstream. Droplet sizes decrease significantly up to the midstream region, while axial velocities increase due to momentum exchange with the crossflow. The sweeping motion of the SES nozzle induces a dominant oscillation frequency of spray characteristics. The amplitude of these oscillations varies spatially, reflecting the combined effects of sweeping dynamics and aerodynamic damping. Compared to the circular nozzle, the SES nozzle exhibits distinct spray characteristics. The circular nozzle demonstrates greater penetration, but the SES nozzle provides wider lateral coverage, a larger overall spray area, and smaller droplets. Injection pressure is found to be a critical parameter governing spray penetration, coverage, droplet size, and oscillatory behavior. Increasing pressure enhances penetration but results in a trade-off with spanwise coverage. At higher pressures, stronger atomization reduces both Sauter mean diameter and oscillation amplitudes. Overall, this work provides insights into the temporal–spatial spray characteristics of SES nozzles in crossflow environments, offering guidance for their application in aerospace propulsion systems.