Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H16: Aerodynamics: Fluid-Structure Interaction I |
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Chair: Lucy Zhang, Rensselaer Polytechnic Institute Room: 204 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H16.00001: The Effectiveness of the Perfectly Matched Layer in Fluid-Structure Interaction Problems Lucy Zhang, Jubiao Yang It is well recognized that spurious reflections on computational domain boundaries can have contamination of the flow field when solving fluid and/or wave equations. The effects are even more pronounced in fluid-structure interaction (FSI) problems, since the solid responses may be distorted due to the contaminated flow field. In this work, we implemented the perfectly matched layer (PML) technique and applied it in our fully-coupled immersed finite element method (IFEM), where Navier-Stokes equations are solved in the fluid domain with finite element method. With PML included as an absorbing layer it successfully absorbs outgoing waves from the interior of the computational domain and therefore keeps them from reflecting back from the computational boundary. Validation cases are shown to demonstrate the effectiveness of the PML in pure computational fluid dynamics cases, and then followed by FSI problems. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H16.00002: Characterizing self-excited fluidic energy harvesters subjected to Vortex Induced Vibration by utilizing Griffin scaling Niell Elvin, Vahid Azadeh Ranjbar, Yiannis Andreopoulos The present work has experimentally characterized energy harvesters consisting of a circular cylinder mounted at the tip of a flexible cantilever beam. VIV phenomena such as lock-in range, maximum amplitude of transverse oscillation and hysteresis effects have been studied by testing different physical parameters such as structural damping, mass ratio, and aspect ratio. Griffin plot generated by the experimental data of SDOF high aspect ratio circular cylinders have been used to validate VIV. As the harvester is a continuous system of low aspect ratio circular cylinders, three cases have been investigated: low aspect ratio effect of cylinders, effect of multiple modes or coupled transverse-torsional oscillation and non-linear effect due to large deformation of flexible cantilever beams. Griffin plot shows large variance in the case of aspect ratios less than 3. Coupled transverse-torsional oscillation affects VIV negatively. Results show that added structural damping due to piezoelectric patches attached to the cantilever beam decreases electrical power output as a non-linear function of mass ratio. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H16.00003: Flow structure interaction between a flexible cantilever beam and isotropic turbulence Andrew Vogel, Thomas Morvan, Oleg Goushcha, Yiannis Andreopoulos, Niell Elvin In the present experimental work we consider the degree of distortion of isotropy and homogeneity of grid turbulence caused by the presence of a thin flexible cantilever beam immersed in the flow aligned in the longitudinal direction. Beams of various rigidities and lengths were used in the experiments. Piezoelectric patches were attached to the beams which provided an output voltage proportional to the strain and therefore proportional to the beam's deflection. The experiments were carried out in a large scale wind tunnel and hot-wires were used to measure turbulence intensity in the vicinity of the beams for various values of the ratio of aerodynamic loading to beam's rigidity. It was found that the flow field distortion depends on the rigidity of the beam. For very rigid beams this distortion is of the order of the boundary layer thickness developing over the beam while for very flexible beams the distorted region is of the order of the beam's tip deflection. Analysis of the time-dependent signals indicated some correlation between the frequency of beam's vibration and flow structures detected. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H16.00004: An Immersed-Boundary method for deformable bodies at high Reynolds numbers Dario De Marinis, Sreenath Krishnan, Marco Donato de Tullio, Michele Napolitano, Giuseppe Pascazio, Gianluca Iaccarino With the aim of accurately simulate the flow-field through gas turbine blades a numerical approach is presented, that couples a massively parallel, finite volume Unsteady Reynolds Averaged Navier--Stokes Equations solver with an efficient structural solver describing the dynamics of deformable bodies, using an iterative coupled approach. The numerical strategy is based on a suitable version of the immersed boundary (IB) technique, which is able to handle rigid and deformable complex geometries in turbulent flows. The structures are discretized by a surface mesh of three-node triangular elements and modeled by means of a finite element method. The solution of the fluid-structure-interaction (FSI) problem produces detailed information of the flow patterns through realistic geometries subject to small deformations at high Reynolds and Mach numbers. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H16.00005: Dynamical behaviors of a thin plate under bypassing flow Angxiu Ni, Qiqi Wang The interaction of air flow and flexible structure could lead to complex dynamic behaviors. Here the motion of a thin plate under a bypassing air flow is numerically investigated. Dimensional analysis is carried out and all pertinent dimensionless parameters are found. The appropriate levels of fidelity needed for modeling the structural and aerodynamic behaviors are studied. The effect of ratios between aerodynamic force, bending force and external compression force on the plate are investigated. In general, the aerodynamic force causes the plate to oscillate, the external compression causes it to buckle, while the bending force tries to keep the plate flat. When the bending force is relatively small and the other two forces are comparable, the airflow strongly couples with the nonlinear feedback of the structure, and the system undergoes chaotic motion. We compare this complex motion at different Mach numbers against the classic high-Mach number result by Dowell. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H16.00006: Fluid-structure Interaction of Rigid and Flexible Wings in Ground Effect Robert Bleischwitz, Roeland de Kat, Bharathram Ganapathisubramani Inspired by trawling bats, combining flexible membrane wings and the vicinity of the ground, an experimental wind tunnel study is conducted at Re = 56,000 to determine the fluid-structure-ground interaction of rectangular, perimeter reinforced low aspect ratio (AR = 2) membrane wings in free flight and ground effect conditions. The pitch angle is varied between $10^\circ \leq \alpha \leq 25^\circ$. Flexible membrane wings are compared with rigid flat plates. Instantaneous lift and drag forces are simultaneously recorded with membrane and flow dynamics (Digital-Image-Correlation + Particle-Image-Velocimetry). The focus of this study involves coupling effects of membrane mode shapes (chordwise + spanwise) and flow structures changing with angle of attack and height over ground. A POD analysis of the flow, membrane vibrations and forces should help to identify aerodynamic beneficial vibration shapes and their impact on flow features such as leading edge and tip vortices. The knowledge is seen to be essential for efficient usage of MAVs with membrane wings in and out of ground effect. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H16.00007: Squirt flow in highly deformable multi-porosity materials Patrick Kurzeja, Katia Bertoldi Squirt flow is a phenomenon that typically occurs in porous structures with more than one length scale, e.g., in fractured rocks or multi-porosity organic material. Due to a heterogeneous pore space, external compression induces fluid flow between the pores of different compressibility and finally causes a delayed and attenuated response. While this phenomenon is well understood in natural materials, little it is known about how to trigger and control it in artificially architected materials.\\ Here, we will first show that squirt flow can occur in highly deformable, fluid-filled artificial materials if overall fluid drainage is prevented and then we will demonstrate how this can be controlled. Interestingly, this viscous-flow mechanism opens avenues for the design of smart materials with delayed stress-strain response (e.g., for high-impact applications) or additional attenuation regimes (e.g., below frequencies of internal resonance). [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H16.00008: Energy Extraction from Fluid Flow Via Vortex Induced Angular Oscillations Amitabh Bhattacharya, Shahajhan H. Sorathiya Using Lattice-Boltzmann simulations, we study angular oscillations of an elliptical cylinder attached to a torsional spring, with the axis placed perpendicular to a uniform flow, at low Reynolds numbers (Re=100 and Re=200). The equilibrium angle and stiffness of the torsional spring is chosen such that the ellipse reaches stable equilibrium at an angle of roughly 45$^{\circ}$ with respect to the incoming flow. This configuration leads to large unsteady torque due to vortex shedding, which in turn can lead to large oscillations of the ellipse, with several frequency modes. Along with measuring the angular oscillations of the ellipse, we also measure the potential for power-extraction from this setup, by attaching an external angular damper to the axis of the ellipse. For low density ratios, the ellipse tends to oscillate within the first quadrant, while, for higher density ratios, the ellipse, due to its tendency to auto-rotate, undergoes very large oscillations. The ellipse locks on to primary and secondary vortex shedding modes over the range of density ratios studied here. The power output of this setup increases with increasing Reynolds number and density ratio, with peak efficiency of 1.7\%. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H16.00009: Globally shed wakes for three distinct retracting foil geometries Stephanie Steele, Michael Triantafyllou In quickly retracting foils at an angle of attack, the boundary layer vorticity along with the added mass energy is immediately and globally shed from the body into the surrounding fluid. The deposited vorticity quickly reforms into lasting vortex structures, which could be used for purposes such as manipulating or exploiting the produced flow structures by additional bodies in the fluid. The globally shed wake thus entrains the added mass energy provided by the initially moving body, reflected by the value of the circulation left in the wake. In studying experimentally as well as numerically this phenomenon, we find that the three different tested geometries leave behind distinct wakes. Retracting a square-ended foil is undesirable because the deposited wake is complicated by three-dimensional ring vorticity effects. Retracting a tapered, streamlined-tipped foil is also undesirable because the shape-changing aspect of the foil geometry actually induces energy recovery back to the retracting foil, leaving a less energetic globally shed wake. Finally, a retracting hollow foil geometry avoids both of these detrimental effects, leaving relatively simple, yet energetic, vortex structures in the wake. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H16.00010: POD Analysis of Flow Behind a Four-wing Vortex Generator Mahdi Hosseinali, Stephen Wilkins, Joseph Hall Wing-tip vortices that persist long after the passage of large aircraft are of major concern to aircraft controllers and are responsible for considerable delays between aircraft take-off times. Understanding these vortices is extremely important, with the ultimate goal to reduce or eliminate delays altogether. Simple theoretical models of vortices can be studied experimentally using a four-wing vortex generator. The cross-stream planes are measured with a two-component Particle Image Velocimetry (PIV) system, and the resulting vector fields were analyzed with a Proper Orthogonal Decomposition (POD) via the method of snapshots. POD analysis will be employed both before and after removing vortex core meandering to investigate the meandering effect on POD modes for a better understanding of it. [Preview Abstract] |
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