Feasibility of penguin geometric features for the biomimetics applications: overview and analysis

Abstract

Penguins display an utmost degree of adaptation to the marine environment as their water locomotion resembles flying, with their flippers demonstrating multimodal functionality. By multimodality of flipper action (two hydrodynamic modes + bipedal gait balance), we mean that flapping performance is dominant in certain periods and, in that case, Strouhal number is important. There are also periods when the steady (non-flapping) mode is dominant, i.e., the flipper acts as a fixed foil; hence both hydrodynamic modes are analysed in this study. Strouhal number from wing-beat frequency and swimming speed is derived across different penguin species, and the effect of flapping amplitude on the Strouhal number is studied. It is established that $\mathrm{St}$ during aquatic flights for maximum cases falls within the theoretical range of higher propulsive efficiency (0.2 < Strouhal number < 0.4), which gives us the confidence to consider penguin wings as an efficient flapping foil in the autonomous underwater vehicle. Moreover, the estimated buoyancy force at lower depth explains how penguin returns to the water surface capitalizing on the high buoyancy force while their wings act as a fixed foil and, that way generate beneficial lift. Then, a numerical analysis was performed to estimate the aerodynamic forces generated by the static penguin wing at a Reynolds number of 60,000 in order to understand its feasibility of application for Micro aerial vehicles. It was found that up to 10° angle of attack, the standard NACA0012 profile shows a higher lift-to-drag, whereas at 15° and 20° angle of attack, as the penguin wing one is 122% and 60.62% higher than the NACA0012 aerofoil. Implementation of scaling the geometric features of penguins for wing design applications is also simulated and discussed.