Manipulation of vortex core characteristics in an expanding swirling flow by multijet injection

The precessing vortex core (PVC) is a fundamental global instability that dictates the dominant unsteady dynamics and energy transfer processes in swirling flows. This study presents a comprehensive experimental investigation of the spatial transformation of the PVC in an expanding swirling flow subjected to multi-jet injection. Using time-resolved particle image velocimetry synchronized with pressure measurements, we systematically quantify changes in key vortex parameters: precession radius, core diameter, helical pitch, and circulation with varying injection angles (axial, radial, and combined). The results demonstrate a profound spatial reorganization: a systematic contraction of the precession radius, a significant axial stretching reflected in an increased helical pitch, and a monotonic reduction in vortex circulation. These spatial modifications are successfully consolidated using the momentum flux coefficient, revealing clear scaling laws. This work establishes a direct causal link between the controlled manipulation of the PVC's spatial topology and the attenuation of its dynamic effects, providing a foundational insight for developing efficient control strategies in vortex-dominated flows.