PIV-Based Characterization of the Hydrodynamic Effects of a Bubble Curtain Intended for Fish Guidance

Bubble curtains are non-physical fish-guidance devices that modify the hydrodynamic and acoustic environment near water intakes. This study quantified the liquid-phase velocity field generated by a bubble curtain placed in the vicinity of a water intake in a laboratory open-channel testing rig using planar Particle Image Velocimetry (PIV). Measurements were carried out at a background water velocity of 0.33 m/s for air-injection rates of 0, 5, 8, 10.5, and 15 L/min. Velocity fields were obtained at distances of 0, 20, 30, and 50 mm from the porous hose, with detailed analysis performed at 20 mm. Bubble regions were identified and masked before liquid-phase image correlation. Air injection modified the local velocity direction and produced localized velocity increases, with a maximum local liquid-phase velocity magnitude of approximately 0.42 m/s. Relative to the no-airflow reference velocity of 0.33 m/s, the spatially averaged velocity magnitude increased by approximately 6.7%, 11.8%, 15.2% and 16.7% at airflow rates of 5, 8, 10.5 and 15 L/min, respectively; however, the incremental increase between consecutive airflow conditions decreased from approximately 4.7% between 5 and 8 L/min to 3.1% between 8 and 10.5 L/min and 1.3% between 10.5 and 15 L/min. The spatially averaged velocity magnitude increased with airflow rate, while the incremental response decreased progressively at higher air-injection rates. Thus, 8 L/min represents a candidate energy-efficient operating condition under the tested laboratory conditions. The results provide hydraulic information relevant to subsequent fish-behavior experiments; however, fish-guidance performance cannot be inferred from the present hydrodynamic measurements alone. The results provide a hydraulic basis for designing subsequent fish-behavior experiments. Because no fish were present during the measurements, the study does not assess fish attraction, avoidance, movement restriction, passage, entrainment, or guidance efficiency. Fish-guidance performance cannot be inferred from the present hydrodynamic measurements alone.