Numerical analysis of flapping sound generated by hovering insects.

Abstract

Insect flapping sound is a consequence of flow disturbance generated by flapping wing motion. Spatial and temporal changes of pressures on the wing surface and vortex structures generated by the wing motion are considerable sources of the flapping sound. To analyze such mechanism in the sound generation, we have developed an integrated method combining computational fluid dynamics (CFD) techniques and acoustic analysis. Unsteady flows around a hovering insect are simulated by NS solution‐based CFD analysis with a multiblocked, moving‐overset grid technique. In the acoustic analysis, monopole and dipole sound sources generated by the wing motion are analyzed by using Ffowcs–Williams and Hawkings method. In this study, numerical analyses of the flapping sounds are carried out for three insects of hawkmoth, honeybee, and fruitfly. The CFD analysis provides a detailed picture of the flow fields around the hovering flyers where complicated vortex aspects and the induced pressure distributions on the wing surfaces show concrete evidence of the sound sources. The acoustic analysis further clarifies the characteristics of the flapping sounds induced by these sound sources, including the sound directivity and its spectrum distribution. These results effectively demonstrate the cause‐and‐effect relationship in sound generation and thus indicate the availability of this integrated CFD‐acoustic method.