Detecting fluid flows with bioinspired hair sensors Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/44558g30m

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  • Many animals detect prey or enhance their locomotion with information from hair-like receptors that are activated by local fluid flows. The utility of biological hair receptors has motivated the design of artificial hair sensors (AHS) for flow control applications where aerodynamic or hydrodynamic forces play a significant role in the dynamics of a body. Among the potential applications for AHS are low-Reynolds number flyers for enhanced maneuverability and underwater vehicles for greater efficiency while navigating. For such applications, how flow phenomena related to aerodynamically or hydrodynamically important forces can be detected through the mechanical response of AHS must be understood. In this collection of manuscripts, we investigate the utility of AHS for detecting flow phenomena pertinent to these applications. One aerodynamically adverse phenomena of low-Reynolds number flight is boundary layer separation. By modeling each hair as a viscoelastic beam coupled to its local flow environment, the dynamic and mechanical response of a hair sensor array was simulated in unsteady flow separation. We show that the resultant moment at the base of each hair sensor in the array provides a space and time accurate representation of the onset and span of reversed flow, the location of the point of zero wall shear-stress, the formation and relative position of near wall vortices, and the spatial development and evolution of boundary layer flows. The shape of a boundary layer flow is another means of detecting flow separation and is also related to the local wall shear-stress. Here, we determine the hair lengths relative to a general measure of boundary layer thickness that maximizes output sensitivity to changes in boundary layer shape. The range of computed optimal hair lengths is in close agreement with the range of hair receptor lengths measured on three bat species. A tapered hair profile is shown to provide larger sensitivities over a wider range of flow conditions compared to hairs of uniform cross section. The feedback of surface mounted AHS measurements for accurate flow state estimation away from the wall is important for effective flow control design. A linear quadratic Gaussian observer is designed for an unsteady viscous incompressible flow with hair sensor arrays. Here, the Riccati equation was numerically solved using the modified Kleinman-Newton method combined with a snapshot procedure for solving Lyapunov equations. We show that measurements provided by two patches of hair sensor arrays significantly contributes to the estimation of a nearby region of the flow velocity field. The results herein support artificial hair sensors as an effective means of detecting flow phenomena important to the dynamics of bodies in fluid flows. Within the following manuscripts, contributions are also made to biology, artificial hair sensor design and application, and linear control theory.
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