Application of a fish-shaped probe at an angled rack: introducing the fish sensory sonde (FSS)

Over the last five decades, an increasing number of studies on fish behaviour in turbulent flows have been carried out, predominantly under laboratory conditions. The majority of these works correlate fish behaviour and time-averaged velocity and turbulence parameters, derived from the fluctuations of the three velocity components. However, fish experience the changing flow field through fluid-body interactions, and thus the comparison of velocity measurements and fish swimming behaviour is always missing the interaction with the flow field, as experienced by fish. This study presents a multiparameter fish-shaped probe which measures flow in a more “fish-like” way – the Fish Sensory Sonde (FSS). The probe body is equipped with three pressure sensors (right, left, center) for mimicking the anterior lateral line, and is also outfitted with an inertial measurement unit (IMU) which acts as a digital vestibular system. An interesting parameter which the FSS provides is the pressure asymmetry, which is directly related to a force imbalance acting on the left and right sides of the fish body. Since fish use undulatory locomotion, regions of a flow field with strongly changing or zero crossing pressure asymmetries are hypothesized as being avoided by fish, and are compared to laboratory studies of live fish in this work. Regions of asymmetric pressure will require constant adjustments to a fish’s body posture relative to the bulk flow field for a fish to maintain its swimming gait. We also show the advantage of a moving FSS probe to provide gapless measurements in a shorter time compared to a stationary probe. The FSS, hence, has the potential to improve future eco- and ethohydraulic investigations by providing new ways and means of measuring fluid-body interactions more similar to that of living fish