Interaction of fluids and thin structures: simulation and applications

Abstract

Interactions between fluids and solid structures of small thickness can be found in many applications, e.g., aerodynamics of the membranous wings of insects, hydrodynamics of fish fins, human heart valves, flags and tree leaves in the wind, and plants under water. In this work, we use an efficient immersed-boundary method as the flow solver and couple it with a structure solver to address some of these problems with practical applications in mind. In the first problem, the aeroelasticity of flapping wings in nature is considered using a two-dimensional model, and the effect of the wing deformation on the aerodynamic performance is studied. The result shows that the wing deformation can significantly enhance the lift and reduce the power consumption. Furthermore,at the same the magnitude of deformation, the low-mass wing consistently has better performance than the high-mass wing in terms of efficiency. In the second problem, the hydrodynamic interaction of several elastic sheets in tandem arrangement is studied, which has been motivated by its application in energy harvesting from the flow. Through the vortex-vortex interaction, the two sheets within certain distance are found to vibrate with great magnitude and in a coordinated manner. The mechanism for such a resonant system behavior is examined, and its extension to multiple sheets is discussed. In the third problem, the numerical method for the fluid/thin-structure interaction is extended to two-fluid flows in complex geometries by combining two types of immersed-boundary method, and drops traveling through a microfluidic channel with asymmetric protrusions is considered as a specific application. The mechanism underlying the formation of an asymmetric interior flow pattern is studied, and the effects of the viscosity ratio and the geometry of the protrusions are discussed. The observed flow patterns could be used for mixing enhancement inside the drops.