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.
Highlights
The thrust and lift produced by the birds can be controlled by using the flapping mechanism of their wings; optimal propulsion in fish can be obtained from the flapping motion of their pectoral and caudal fins.1 The dorsal fin on the fish is helpful for achieving their maneuverability
To understand the underlying physical mechanisms governing the propulsion and jet deflection of side-by-side foils in a still medium, we focus our efforts on three questions, in particular: (1) how do the propulsive characteristics vary as a function of the oscillation phase difference between the foils and the frequency of oscillation? (2) how do jet deflection angles vary as a function of oscillation phase difference and frequency of oscillation? (3) what are the wake dynamics of pitching foils arranged in a side-by-side configuration in a still medium? Hopefully, the present work imparts insights to understand the maneuverability of UAVs, which can be obtained from the jet deflection
The momentum equation is reformulated in the Arbitrary Lagrangian–Eulerian (ALE) form to take into account the effect of moving boundaries
Summary
The thrust and lift produced by the birds can be controlled by using the flapping mechanism of their wings; optimal propulsion in fish can be obtained from the flapping motion of their pectoral and caudal fins. The dorsal fin on the fish is helpful for achieving their maneuverability. The wake interference becomes vital for the case with a smaller foil–foil gap and induces the inverted Bénard–von Kármán vortex streets Their results show that the hydrodynamic performance of two anti-phase flapping foils can be significantly different from that of an isolated pitching foil. Their study suggests that the switching of the vortex pattern is found to be the primary reason that a deflected asymmetric wake reverses its deflection angle They found that the deflection angle increases with the strength of the vortex pairs, which depends on the heaving amplitude, frequency, and free stream Reynolds number. To the best of our knowledge, limited literature is available, which deals with the jet deflection that can be obtained by changing the oscillation phase difference between the airfoils arranged in a side-by-side configuration.
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