Dr. José Alvarado, MIT

"Nonlinear Response of Soft Hair Flows"

Abstract: We are "hairy" on the inside: surfaces such as intestines, tongues, and blood vessels comprise beds of fibers immersed in fluids. Fluid flows deform hairs — but hair deformation affects fluid flows. We investigate these mechanics by measuring the flow response of artificial hair beds and developing a theoretical model.

We identify two nonlinearities. First, a drag-reducing nonlinearity occurs when hairs bend down and widen the gap through which fluid flows. We hypothesize biological hairs reduce drag in-vivo via this nonlinearity. Second, a rectification nonlinearity occurs when fluid flows against the grain of angled hairs. Rectification can be used to build microfluidic diodes and pumps for various applications, including miniature hydraulic robots.