Description
- Abstract:
- We present experimental investigations on two classes of problems that are inspired by bat flight—vortex wakes and compliant membrane wings. Aerodynamic experiments with flapping animals (such as bats and small birds) receive considerable attention because the unique approaches to low Reynolds number flight (Re < 200,000) that animals employ may offer clues to engineers designing small autonomous aircraft that operate under similar flight conditions. Previous particle image velocimetry (PIV) measurements of bat and bird wakes have struggled to draw quantitative conclusions about the aerodynamic forces generated in flight. We performed a detailed analysis of PIV wake measurements, determined the criteria for making accurate measurements, and implemented a dual-plane PIV technique that satisfies these criteria and improves the dynamic range of wind tunnel wake measurements. The increased dynamic range of dual-plane PIV permits accurate aerodynamic force predictions from PIV measurements in the wake of Seba's short-tailed bats and allows the direct calculation of the aerodynamic cost of flight from the kinetic energy observed in the wake. One of the unique features of bat morphology is their membraneous wing skin. We developed a simple model of the finite deformation and natural frequency of an initially tension-free membrane wing, which depends only on an aeroelastic parameter and shows good agreement with experiments on low aspect ratio membrane wings with different support structures and thicknesses, over a broad range of flight parameters. Coupled membrane shape, aerodynamic force, and PIV wake measurements indicate that membrane deformation affects the membrane vibration modes, which in turn affects the coupling between the membrane and vortex shedding. Wings with different wing tip support but similar stiffness may show similar static behavior but exhibit markedly different dynamic behavior. The details of the membrane support play an important role in the fluid-structure interaction. Our experiments show that freely fluttering wing tips disrupt the structure of the tip vortices, leading to a diffuse, erratic vortex structure and reduced aerodynamic performance at high angle of attack compared to the tip vortices formed on rigidly supported membrane wings.
- Notes:
- Thesis (Ph.D. -- Brown University (2014)
Access Conditions
- Rights
- In Copyright
- Restrictions on Use
- Collection is open for research.
Citation
Waldman, Rye M.,
"Vortex Wakes and the Mechanics of Membrane Wings—Problems Inspired by Bat Flight"
(2014).
Fluid, Thermal, and Chemical Processes Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z09S1PF8
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Fluid, Thermal, and Chemical Processes Theses and Dissertations
Theses and Dissertations for the Fluid, Thermal, and Chemical Processes department....