Effects of the flapping frequency on the thrust performance for three-dimensional bionic multi-wings in a schooling

Abstract

The excellent performance of many creatures using flapping wings has attracted a lot of research on the performance of a single flapping wing. However, many species generally choose highly organized movements rather than alone in the animal world; there is a very popular and interesting biological clustering phenomenon known as schooling. Understanding the flow mechanisms and thrust performance of flapping multiwings in a schooling could be applied to novel bionic flapping wing aircraft formation design. We perform numerical simulations employing the immersed boundary-lattice Boltzmann method for flow over a single flapping wing and the flapping multiwings in a diamond schooling at different St numbers. Meanwhile, the effects of the difference in individual flapping frequency on the overall propulsive performance of the schooling were investigated. We present the spectra of aerodynamic forces for a single flapping wing and each wing in a diamond schooling at different individual flapping frequencies. Numerical results indicate that the flapping frequency has great effects on the thrust performance of a single wing and the multiwings in a schooling. The average thrust coefficient of a single flapping wing grows with the increase in the St. However, there is an optimal St number to obtain the maximum propulsive efficiency. For a schooling that maintains the same flapping frequency, the overall schooling or each wing in a schooling shows the same trend as a single wing. For a schooling with different individual flapping frequencies, the aerodynamic characteristics of the last downstream wing are more affected by the frequency difference.