Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M10: General Fluid Dynamics II |
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Chair: Heidi Nepf, Massachusetts Institute of Technology Room: 313 |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M10.00001: Numerical simulation of a plunging flexible hydrofoil and its experimental validation Tao Yang, Leonardo Martin-Alarcon, Mingjun Wei, Fangjun Shu A monolithic approach for simulation of flexible flapping wings in fully-coupled motion has recently been developed. The methodology is based on a uniform description of fluid and structure in Eulerian framework. Immersed boundary technique is used to represent solid stress, solid-fluid interface, and active flapping motion in an overall Cartesian coordinate. In the current presentation, the focus is to apply the method on a simple two-dimensional problem of plunging flexible hydrofoil and then compare to the experimental results for validation. The three-dimensional results and experimental validations will also be discussed. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M10.00002: Experimental study of flow field around a plunging flexible hydrofoil Leonardo Martin-Alarcon, Tao Yang, Fangjun Shu, Mingjun Wei Recent developments in micro air vehicles (MAVs) have led to the improvement of computational fluid dynamics (CFD) simulations capable of simulating flexible flapping wing phenomena. For validation of these simulations, an experimental methodology is applied to characterize the flow physics involved with an immersed flexible flapping hydrofoil. Using a one-degree of freedom crank-shaft system, a silicone hydrofoil was actuated to flap under various kinematic conditions. The hydrofoil was subject to active plunging and passive pitching motion in both water and aqueous glycerin solutions. Phase-locked particle image velocimetry (PIV) measurements were obtained around the flapping hydrofoil. These measurements, along with force measurements using a six-axis load cell, are used to compare the results with those of the numerical simulations. By comparing the hydrofoil deformation, vortex evolution and force generation, good agreements between CFD and experimental results were observed. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M10.00003: The analysis of three dimensional flow around a low-aspect-ratio control fin with end plate Chulmin Jung, Kurnchul Lee, Chanki Kim Flow around the tip of control fin is fully three dimensional, and the prediction of lift on the control fin is essential in maneuvering a vehicle in an appropriate manner. Three dimensional flow effect on a low- aspect-ratio control fin is more obvious than on a moderate or high-aspect-ratio control fin. The three dimensional flow effect can be reduced by applying end plate. Through numerical simulations, we examine the flow field around a low-aspect-ratio control fin with and without end plate for different flap angles. The pressure, vorticity, lift and torque on the control fin are analyzed and compared to experiments. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M10.00004: Effect of gust on flow patterns around a robotic hummingbird wing Eloy N.M. Gonzalez, B.J. Balakumar, Fangjun Shu Several studies have demonstrated the importance of the leading edge vortex in enhancing lift production during hovering flight for a hummingbird. Most of these studies were performed under steady inflow conditions. However, real-life ornithopters in the field have to routinely tackle directional changes in the wind and gust. In this work, we investigate flow field variations around a hummingbird wing under well-controlled gust conditions using a 2-degree of freedom robotic model in a water channel. Conditions of gust are simulated by mounting the model on a translation stage, which allows the control of gust profiles. Phase-locked and time-resolved particle image velocimetry (PIV) measurements were obtained around the wing in the presence of various gust levels. These measurements, in combination with force and moment measurements using a six-axis load cell, are used to understand transient flow phenomena induced by the gust, and their effect on the net thrust and lift forces over a range of Reynolds number (2100$<$Re$<$30000). [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M10.00005: Drag on Flexible, Slender Bodies Streamlined in Turbulent Flow Jeffrey Rominger, Heidi Nepf Dynamic reconfiguration in response to turbulent fluid forcing alters the instantaneous drag forces on flexible, slender bodies, such a submerged aquatic plants. In this study we experimentally investigate the role of plant morphology, specifically length and structural stiffness, in reducing instantaneous drag forces on flexible plastic strips streamlined in turbulent flow. We limit this investigation to the stable regime of fluid- solid interactions, which is typical of many species of submerged aquatic vegetation. First the structural stiffness of the flexible strips is varied to determine how bending in response to turbulent fluid forces can alter instantaneous drag forces. We also investigate the role played by the ratio of the turbulence lengthscale to the length of the plastic strips. When the turbulence lengthscale is similar to or larger than the strip length, turbulent forces can act coherently over the length of the strip, which may enhance instantaneous forces. In contrast, when the turbulence lengthscale is smaller than the strip, the instantaneous forces can be non-coherent and interfere destructively, reducing the effect of the instantaneous forces on the strip. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M10.00006: Flow-induced oscillations of a pipe conveying fluid with base excitation Gary Chang, Yahya Modarres-Sadeghi We study various dynamic instabilities in a cantilevered pipe conveying fluid with base excitation. A plain cantilevered pipe conveying fluid loses its stability by a Hopf bifurcation, leading to either planar or non-planar flutter for flow velocities beyond the critical flow velocity for the Hopf bifurcation. If a mass is attached to the end of the pipe (a so-called added mass), the resulting dynamics becomes much richer, showing 2-D and 3-D quasi-periodic and chaotic oscillations at high flow velocities. In this work, we consider a cantilevered pipe subjected to either a periodic base excitation, or a periodic point excitation at a given location along the pipe,~and study the response of the fluid-conveying pipe in 2-D and 3-D. It turns out that by selecting the right frequency and amplitude for the external excitation, we can force the non-planar oscillations to planar ones. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M10.00007: The Hydrodynamic Optimization of a Cable-Flying Vehicle Brian Amaral Profiling the water column with high vertical and horizontal resolution in the deep ocean from a moving vessel is difficult with the current tools. Thus, a new, higher resolution-capable wire-flying vehicle, the WiFly, is being designed to profile the water column. The WiFly traverses up and down a ship-towed cable by generating lift from wings that protrude from the sides of vehicle. Because the success of the vehicle is based on its glide slope performance, the ratio of vertical velocity to horizontal velocity, the shape of the vehicle must be optimized for the flow conditions associated with its anticipated uses in oceanographic science. Results include evaluation methods, body shapes, and the parameters involved in selecting the most desirable shape characteristics. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M10.00008: Physics of badminton shuttlecocks. Part 1 : aerodynamics Caroline Cohen, Baptiste Darbois Texier, David Qu\'er\'e, Christophe Clanet We study experimentally shuttlecocks dynamics. In this part we show that shuttlecock trajectory is highly different from classical parabola. When one takes into account the aerodynamic drag, the flight of the shuttlecock quickly curves downwards and almost reaches a vertical asymptote. We solve the equation of motion with gravity and drag at high Reynolds number and find an analytical expression of the reach. At high velocity, this reach does not depend on velocity anymore. Even if you develop your muscles you will not manage to launch the shuttlecock very far because of the ``aerodynamic wall.'' As a consequence you can predict the length of the field. We then discuss the extend of the aerodynamic wall to other projectiles like sports balls and its importance. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M10.00009: Analysis of the Free Rising Sphere in Newtonian Fluid and the ``Pop Off'' Effect Anna Shchetinina, Julio Garcia, Emmanuel Gaillard, Lyes Kadem, Hoi Dick Ng In this experiment motion of a free rising sphere in Newtonian fluid is studied. Spheres of various densities and diameters are placed at the bottom of a large water tank and then released with zero initial velocity and no distortion in trajectory. The motion of the rising sphere is described in three phases: ascending, where the body undergoes constant acceleration and moves vertically while developing vortices on its both sides; transitional, where a secondary sideway motion is added and vortex shedding begins; and, finally, oscillatory, where the sphere begins to move in a sinusoidal pattern while describing even spiral trajectory. The mode in which the ball exits the water varies depending on several conditions. Depending on the Reynolds number, it escapes vertically or diagonally, which is referred to by Bourrier et al. (1984) [Eur. J. Phys. 5:225-231] as the `pop off' effect. Using Particle Image Velocimetry (PIV), high-speed photography and image processing techniques, we discuss the causes of the oscillatory motion as well as the ``pop off'' effect produced by a sphere under placed conditions. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M10.00010: Tubular jet generation by means of a pressure pulse induced by an eddy-current actuator Alexander Klein, Ivo R. Peters, Gerben Morsink, Chao Sun, Devaraj van der Meer, Robert Giezendanner-Thoben, Detlef Lohse The generation and the evolution of tubular jets is studied experimentally and compared to numerical results from a boundary integral code. The jets are created at the free surface above a liquid column of purified water. An eddy-current actuator driven by a high voltage capacitor bank is used to create a pressure pulse with a duration of about $100~\mu\mathrm{s}$ and varying amplitude of up to $70~\mathrm{bar}$. The pressure pulse travels in the vertical water column of length 1 m before hitting the free surface in a capillary tube of $4-8~\mathrm{mm}$ in diameter. The process of jet formation is captured using high-speed imaging at up to $60~\mathrm{kHz}$, while the pressure pulse is recorded by two PVDF transducers at $20~\mathrm{MHz}$. The recordings and the numerical simulations enable us to study the effect of the control parameters on the jet velocity (which can reach up to $50~\mathrm{m/s}$) and the mass flow. Namely, we study the effect of the applied acoustic power of the pressure pulse and the initial curvature of the free surface. [Preview Abstract] |
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