Jet deflection by two side-by-side arranged hydrofoils pitching in a quiescent fluid

Abstract

The present work reports a computational study on the pitching of two identical NACA 0012 airfoils arranged in a side-by-side (parallel) configuration in a still medium. Pitching of airfoils arranged in a side-by-side (parallel) configuration in a still medium leads to the formation of a deflected jet. The angle at which the jet is deflected depends on the oscillation phase difference between the airfoils and the frequency of oscillation. The deflection angle is high at a lower frequency of oscillation for a given phase difference between the foils. The time-averaged jet deflection angle, thrust, and lift on airfoils are quantified for a range of frequencies (0.5 Hz–2 Hz) and phase differences (0°–180°) between the airfoils. The thrust force increases gradually with an increase in the phase difference between the foils until 120°, and beyond this, it decreases. The maximum jet deflection angle is found to be 28° when the phase difference is 45° for a frequency of 0.5 Hz. It is observed that the initially deflected jet switches toward the centerline position after specific periods of pitching. This switching of the jet from a deflected position toward the centerline initiates once the vortices from the lower foil interact completely with the upper foil. Some of these findings are relatively new in the domain of bio locomotion, which is useful for various related engineering applications.