Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E32: Focus Session: Vortex Dynamics in Fluid-Structure Interactions III |
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Chair: Silas Alben, University of Michigan Room: 33C |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E32.00001: Numerical Simulation of the Dynamic FSI Response and Stability of a Flapping Foil in a Dense Fluid Eun Jung Chae, Deniz Tolga Akcabay, Yin Lu Young To advance the understanding of fish locomotion, improve the design biological devices or marine propulsions or turbines, or to explore innovative ocean energy harvesting ideas, it is important to be able accurately predict the dynamic fluid structure interaction (FSI) response and stability of flexible structures in a dense fluid. The objectives of this research are to (1) present an efficient and stable algorithm for numerical modeling of the dynamic FSI response and stability of a flapping foil in dense fluid, and (2) investigate the influence of fluid-to-solid density ratio on the FSI response and stability of a flapping foil. The numerical model involves coupling an unsteady RANS solver with a 2DOF structural model using a new hybrid coupling approach. The results show that the new hybrid coupling approach converge much faster than traditional loosely and tightly coupled approaches, and is able to avoid numerical instability issues due to virtual added mass effects for light, flexible structures in incompressible flow. The influence of density ratio on the FSI response, divergence and flutter speeds are presented, along with comparisons between viscous and inviscid FSI computations. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E32.00002: A parametric study of thrust and efficiency of an oscillating airfoil A.W. Mackowski, C.H.K. Williamson An oscillating airfoil serves as a classic test case for a variety of unsteady phenomena in fluid mechanics. In nature, fish, birds, and insects oscillate their fins and wings to produce thrust and maneuvering forces, often studied by approximating the appendages as airfoils. On the other hand, the unsteady fluid mechanics of an oscillating airfoil involve vortex shedding and vortex advection, which are essential to understanding unsteady thrust, and worth studying in their own right. This information is useful in areas such as flow control, fluid-structure interaction, and undersea robotics. In this work, we examine the thrust and efficiency of a heaving (or pitching) foil as a function of variables such as the reduced frequency and amplitude (noting previous related studies such as Koochesfahani 1989; Anderson et al. 1998). Further, our novel experimental ``cyber-physical'' technique [Mackowski {\&} Williamson, 2011] allows the airfoil to propel itself under its own thrust. Our experimental apparatus constantly monitors the fluid forces acting on the foil, and commands velocity to a carriage system in accordance with these forces. With this capability, we are able to measure the terminal velocity of a self-propelled airfoil, as well as its stationary thrust and efficiency. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E32.00003: Aerodynamic cause of the asymmetric wing deformation of insect wings Haoxiang Luo, Fangbao Tian, Jialei Song, Xi-Yun Lu Insect wings typically exhibit significant asymmetric deformation patterns, where the magnitude of deflection during upstroke is greater than during downstroke. Such a feature is beneficial for the aerodynamics since it reduces the projected wing area during upstroke and leads to less negative lift. Previously, this asymmetry has been mainly attributed to the directional bending stiffness in the wing structure, e.g., one-way hinge, or a pre-existing camber in the wing surface. In the present study, we demonstrate that the asymmetric pattern can also be caused by the asymmetric force due to the flow, while the wing structure and kinematics are symmetric. A two-dimensional translating/pitching wing in a free stream is used as the model, and the wing is represented by an elastic sheet with large displacement. The result shows that, interestingly, the wing experiences larger deformation during upstroke even though the aerodynamic force is greater during downstroke. The physical mechanism of the phenomenon can be explained by the modulating effect of the aerodynamic force on the timing of storage/release of the elastic energy in the wing. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E32.00004: Aerodynamic performance of membrane wings with adaptive compliance Oscar M. Curet, Alexander Carrere, Arjun Pande, Kenneth S. Breuer Some flying animals use wing membranes with adaptive compliance to control their aerodynamic performance. In this work we characterize the mechanical properties and aerodynamic performance of a low aspect ratio membrane wing composed of a dielectric film supported on a rigid frame. We test the wing model in a wind tunnel. When a fixed voltage is applied across the wing membrane the camber increases, accompanied by a small increase in lift (less than 2\%). However, lift is significantly increased when the wing is forced with an oscillating field at specific frequencies that correspond to the characteristic vortex shedding frequency. We present the results concerning the kinematics and aerodynamic performance of the adaptive wing membrane and the coupling between the vortex shedding and the forced modulation of elastic modulus. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E32.00005: Vortex interactions with membrane wings Rye M. Waldman, Kenneth S. Breuer Membrane wings are common in flying animals such as bats, as well as in low Reynolds number Micro Air Vehicles. Vortices shed from the sharp leading- and trailing-edges and wing-tips of membrane wings, and the vortex interactions with the membrane play an important role in the wing's performance. When looking at compliant membrane wings that are initially tension-free at rest, there are two issues to consider: the static relationship between the net aerodynamic forces and the bulk wing deformation and the interaction between the membrane dynamics and unsteady flow structures. Nonlinear membrane deformation affects the membrane vibration modes, which in turn affects the coupling between the membrane and vortex shedding. We present coupled force, kinematic, and flow field measurements on low aspect ratio membrane wings of different thickness, with and without wing-tip support, over a range of angles of attack and freestream velocities. Wings with different tip support but of similar stiffness show similar static behavior, but different wing dynamics result in markedly different behavior in both the unsteady forces and the character of stall at high incidence angles. [Preview Abstract] |
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