Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session Q14: Aerodynamics: Fluid Structure Interaction III |
Hide Abstracts |
Chair: Ahmed Naguib, Michigan State University Room: Georgia World Congress Center B301 |
Tuesday, November 20, 2018 12:50PM - 1:03PM |
Q14.00001: A unified continuum and variational multiscale formulation for fluids, solids, and fluid-structure interaction Ju Liu, Alison L Marsden Computational fluid-structure interaction (FSI) still faces several fundamental challenges. For example, in the classical FSI formulation, it is impossible to handle incompressibility in the solid model. The monolithic coupling approach, although more robust than the staggered approach, is still not well-accepted because it is complicated to implement and to solve. In this talk, I will present a unified continuum modeling framework for viscous fluids and hyperelastic solids using the Gibbs free energy as the thermodynamic potential. Then we perform variational multiscale (VMS) analysis for this continuum body, which recovers the residual-based VMS formulation for the Navier-Stokes equations and provides a mechanism to circumvent the inf-sup condition for discretizing the solid problem. After that, I will discuss a novel unified formulation for fluid-solid coupled problems, which enjoys several appealing properties. The temporal scheme is more robust and more accurate in all Fourier modes. One can design an efficient and robust iterative solution method by using the algebraic multigrid method. More importantly, the new FSI formulation is straightforward to implement based on an existing CFD code. The connection between FSI and multiphase flow problems will be discussed. |
Tuesday, November 20, 2018 1:03PM - 1:16PM |
Q14.00002: Influence of surface topology on the wake development behind circular and rectangular cylinders Kian Kalan, Ahmed Naguib, Manoochehr Koochesfahani Suspension lines of precision airdrop systems are susceptible to galloping instability, resulting in large-amplitude self-sustained vibration and increased drag. The cross section of these suspension lines is typically non-circular and resembles a rectangle with rounded corners. Additionally, the surface is not smooth and is characterized by topological features. As part of an effort to understand the basic characteristics of the flow field around suspension lines, the current work focuses on the wake development and how it is affected by changes in the shape of the cylinder cross section and surface topology. Molecular tagging velocimetry (MTV) is employed to measure the flow velocity field for cylinders with circular and rectangular cross section, each contrasting the influence of prescribed surface topology compared to a smooth surface. Results will be presented for downstream development of the wake in terms of mean and fluctuating streamwise velocity component and wake closure length. |
Tuesday, November 20, 2018 1:16PM - 1:29PM |
Q14.00003: Experimental investigation of the galloping instability of rectangular cylinders at Reynolds numbers between 1000 and 10,000 Mark A Feero, Ahmed Mostafa Naguib, Manoochehr M Koochesfahani Transverse galloping occurs when oscillation in the direction normal to the approach stream of an elastically mounted body causes the aerodynamic force in the same direction to become amplified and sustained. The motivation for this work derives from a recent study (Seifers et al., AIAA 2013-0064) suggesting that galloping could cause large-amplitude vibration of the suspension lines of precision airdrop systems. To first approximation, the cross-sections of these suspension lines resemble a rectangle with rounded corners, and they operate in the Reynolds number range less than 10^{4}. This work represents a systematic experimental investigation of the effects of geometry on galloping of rectangular cylinders for Reynolds numbers between 1000 and 10,000. The geometric parameters of interest are the ratio of the chord to thickness and the ratio of the corner radius to the thickness. These parameters are varied from 1 to 3 and 0 to 0.5, respectively. Direct measurements of lift and drag variation with angle-of-attack are used to compute the transverse force and assess the susceptibility to galloping. Surface pressure distributions are also measured for selected cases to connect the force behavior to the flow conditions. |
Tuesday, November 20, 2018 1:29PM - 1:42PM |
Q14.00004: Experimental study on flow-induced vibration of two high mass ratio flexible cylinders in tandem arrangement Banafsheh Seyed-Aghazadeh, Nathaniel Anderson Flow-induced vibration (FIV) of two tandem flexible circular cylinders is studied, experimentally. Two identical cylinders with an aspect ratio of 47 and a mass ratio of 120 were held fixed at both ends and placed horizontally in the test-section of a subsonic wind tunnel. The downstream trailing cylinder lied in the wake of the upstream one and the dynamic response of the cylinders are studied for center-to-center spacing range from 3 to 7 times the cylinder diameter. Amplitudes and frequencies of oscillation are studied in the reduced velocity range of U*=3.6-63 and the Reynolds number range of Re = 187-1530. In previous studies on FIV of tandem flexible cylinders, either higher modes of the vibration than the first were not excited in the flow ranges tested or the cylinders had asymmetric boundary conditions at two ends. In the current wind tunnel experiments on FIV of two tandem flexible cylinders despite the high mass ratio of the cylinders, higher modes of vibrations up to the 4^{th} mode in the crossflow direction are excited owing to the high-flexibility of the cylinders. In addition, the cylinders are fully submerged in uniform flow and the boundary conditions are carefully controlled to be symmetric. |
Tuesday, November 20, 2018 1:42PM - 1:55PM |
Q14.00005: Flow-induced vibrations of a rotating cylinder in an arbitrary direction Remi Bourguet An elastically mounted circular cylinder, immersed in a cross-current and forced to rotate about its axis, represents a paradigm to explore the impact of symmetry breaking on flow-structure interactions. Previous works have shown that when the rotating body is free to translate in the direction normal to the current, its responses are comparable to the vortex-induced vibrations (VIV) developing in the absence of rotation, regardless the value to the rotation rate: synchronization of wake unsteadiness and body motion, bell-shaped evolution of the vibration amplitude as a function of the reduced velocity (inverse of the oscillator natural frequency). On the other hand, when the direction of motion is aligned with the current, the system undergoes, at high rotation rate, a switch from VIV-like oscillations to galloping responses, with amplitudes continuously increasing with the reduced velocity. The transition between the contrasted behaviors observed in these two configurations remained to be clarified; this is the object of the present numerical study, where the orientation of the vibration plane is introduced as a new parameter of the problem. Particular attention is paid to the emergence of the galloping-like response regime and its possible modeling by a quasi-steady approach. |
Tuesday, November 20, 2018 1:55PM - 2:08PM |
Q14.00006: Flutter of a semi-flexible cantilever in a cylinder's wake Veera Sajjanapu, Thomas Ward We present an experimental study of the dynamics of flexible structures in a cylinder's wake using a vertical soap film tunnel. Experiments were conducted for two flexible cantilever beams of single rigidity modulus 6000 Pa mm^{4} with difference lengths resulting in Reynolds numbers 5000 < Re < 25000. Cantilevers at zero angle of attack were placed downstream of a cylinder with cylinder radii values ranging from 30-120% of the cantilever lengths. The study was conducted for three downstream gap distances from the cylinder's trailing edge to the cantilever's fixed leading edge. The cantilever motion and wake vortex structure are visualized and analyzed to estimate vibrational amplitudes, frequencies and aerodynamic loading. The beam vibration and vortex shedding results indicated possible flutter phenomena. Assuming small vibrational amplitudes, we consider the Euler-Bernoulli beam theory to estimate flutter derivatives. For the longer cantilever beam we observe evidence of second mode vibration as we increase Reynolds number. |
Tuesday, November 20, 2018 2:08PM - 2:21PM |
Q14.00007: Flutter derivatives for 1-DOF bridge decks using semi-flexible cantilevers Sara Oliveira Santos, Benjamin Ahn, Thomas Ward Identification of aeroelastic coefficients (flutter derivatives) is used in predicting the behavior of bridge decks subject to wind loading. Several methods have been documented for extracting these coefficients from wind tunnel tests, using both free and forced vibration cases, for decks attached to springs. In this talk we discuss extraction of flutter derivatives from soap film tunnel experiments using scale models of three bridge decks attached to cantilever beams. The system was modeled using the Euler-Bernoulli (EB) beam equation with an added mass at the tip. Results from the EB beam equation were used to estimate flutter derivatives for small amplitude vertical displacements. With the soap film tunnel we were able to observe both vortex-induced vibrations (VIV) and flutter for different bridge deck models, and we describe the transition between these two states in terms of the reduced velocity. We discuss how these results may be used to design vibration based energy harvesters. |
Tuesday, November 20, 2018 2:21PM - 2:34PM |
Q14.00008: The influence of a plate’s buckling instability on the early onset of large oscillatory motions Diego F Muriel, Edwin A Cowen We study the onset of large oscillatory motions of a thin elastic plate buckled into a second mode-like deformation created by an applied external net compressive force. We subject the deformed plate to an incompressible flow to induce oscillations, and document three states of motions with the aid of image-based edge detection, acoustic Doppler velocimetry, and particle image velocimetry: a) weak perturbations below a critical flow velocity (Uc), b) large oscillatory motions above Uc, and c) chaotic oscillatory motions above a transitional flow velocity (Ut). We find an early onset of flapping of the deformed plate compared to flag- or inverted-flag type configurations (i.e., lower Uc), where the main physical mechanisms contributing to the reduced Uc are the destabilizing action of the compressive force, a deformed locally-stable plate, and a non-zero pressure drag, all existent prior to structural oscillations. A mathematical model of the structure coupled with the fluid through slender body theory, provides insights on the contribution towards a reduced Uc from the combined destabilizing influence of the net compressive force, and Coriolis and centrifugal forces. |
Tuesday, November 20, 2018 2:34PM - 2:47PM |
Q14.00009: Local Stability Theory of High-Speed Boundary Layers over Compliant Panels Fabian Dettenrieder, Daniel Bodony Boundary layer stability mechanisms have been extensively studied for various flow configurations in order to predict transition to turbulence. The underlying assumptions of a rigid structural domain, however, restrict the application of numerical results away from more realistic flight conditions. In order to capture the potential influence of structural compliance in the presence of a grazing flow, we analyze the canonical problem of a flat plate laminar boundary layer over a mechanically compliant wall. Local linear stability theory - both in temporal and spatial framework - in combination with the thin plate theory suggests a distinct region of fluid-structural coupling in the non-dimensional structural parameter plane. Non-dimensional fluid parameters, namely Reynolds, Mach number, and perturbation frequency, have only a minor impact on the boundary of this region, which allows for quantification of the impact boundaries to predict fluid-structure interaction of a given system. |
Tuesday, November 20, 2018 2:47PM - 3:00PM |
Q14.00010: Hydroelastic Damping of Low Aspect Ratio Plates Eetu Antero Kohtanen, R. Benjamin Davis Motivated by the need to characterize flow-induced damping effects in rocket engine turbomachinery, this study numerically and experimentally considers the hydroelastic damping of low aspect ratio flat plates undergoing free vibration in flowing water. An unsteady, three-dimensional vortex lattice model is coupled to a linear structural dynamic model to predict flow-induced damping as a function of reduced velocity. Experimental investigations involving plates of various aspect ratios and thicknesses are conducted in a high-speed water tunnel to validate the numerical model. The tests involve flow velocities well below those corresponding to hydroelastic instability, and the results from this flow regime indicate that hydroelastic damping is negligibly low and constant until a certain flow speed is achieved. Beyond this speed, hydroelastic damping is found to increase roughly linearly with increasing flow velocity. The results can be used to refine the structural dynamic assessments of rocket engine components, such as turbopump inducer blades. |
Tuesday, November 20, 2018 3:00PM - 3:13PM |
Q14.00011: The Flow and Heat Transfer Enhancement Mechanisms of Autonomous, Aero-Elastically Fluttering Reeds Sourabh Jha, Ari Glezer The limits of low Re forced convection heat transport within high aspect ratio, rectangular mm-scale channels that model air-cooled heat exchangers are overcome by the deliberate formation of unsteady small-scale motions induced by autonomous aero-elastic fluttering of cantilevered, planar thin-film reeds. The coupled flow-structure interactions between the fluttering reeds and the embedding channel flow and the formation, evolution, and advection of the induced unsteady small-scale motions are explored using video imaging and high-resolution PIV. Concave/convex undulations of the reed’s surface that are bounded by the channel’s walls engender the formation and transport of cells of spanwise vorticity concentrations of alternate (CW and CCW) sense. It is shown that the shedding of these vortices is accompanied by energy transfer from large to small flow scales and a concomitant increase in TKE throughout the channel whether the base flow is laminar or turbulent. The TKE increment is accompanied by enhancements in channel heat transfer, as characterized by Nu, which increases with Re. The losses associated with driving the reeds can be effectively managed by reducing the reed’s characteristic flutter frequency with minimal penalty in Nu enhancements |
Tuesday, November 20, 2018 3:13PM - 3:26PM |
Q14.00012: Can the Magnus effect destabilize a ball supported in a jet? Magnus Vartdal, Frank Ham It is well known that it is possible to stably support a ball in a gravitational field using a fluid jet. To what extent this “stable state” is dependent on the rotational motion of the ball is, however, unclear. At the same time, it is known that a rotating body induces significant lift through the Magnus effect. This suggests that the stability of the system may be dependent on the moment of inertia of the ball. In this work, we conduct a computational study, using a moving mesh Navier-Stokes solver, where we systematically vary the moment of inertia of the ball to isolate its effect on the dynamics of the system. Preliminary results suggest that the system remains stable as the moment of inertia becomes large. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2023 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700