Correlating Spatial and Dynamic Responses of a Precessing Vortex Under Multi-Jet Actuation

The precessing vortex core (PVC) in the draft tube of a Francis turbine at part load produces severe pressure pulsations that threaten structural integrity. Efficient active control of PVC demands an understanding of how momentum injection alters the spatial topology and coherent energy of this global instability. This experimental study, conducted on a canonical expanding swirling flow with ten actuators delivering axial, radial, and combined jets, employs synchronized planar PIV and wall-pressure measurements to capture the velocity and pressure fields. Robust correlations are obtained: on-axis and vortex core tangential velocity fluctuations are linearly coupled, circulation scales linearly with precession radius, and helical pitch increases as the precession orbit contracts. Notably, the wall-pressure amplitude depends quadratically on the PVC’s turbulent kinetic energy contribution, showing that spatial contraction enhances the attenuation. These interlinked scaling laws provide a physics-based framework connecting control input to vortex reconfiguration and dynamic load, guiding low-energy control design for hydraulic turbines and other swirling flow devices.