Probing into the Efficacy of Discrete Forcing Immersed Boundary Method in Capturing the Aperiodic Transition in the Wake of a Flapping Airfoil
01 Jan 2021-pp 271-281
TL;DR: In this paper, the authors investigate the underlying flow physics behind the transition from periodicity to aperiodicity in the flow past a harmonically plunging elliptic foil as the plunge amplitude is increased to a high value.
Abstract: The present work focuses on investigating the underlying flow physics behind the transition from periodicity to aperiodicity in the flow past a harmonically plunging elliptic foil as the plunge amplitude is increased to a high value. Two-dimensional (2D) numerical simulations have been performed in the low Reynolds number regime using an in-house flow solver developed following the discrete forcing Immersed Boundary Method (IBM). To capture the aperiodic transition in the unsteady flow-field behind a flapping foil accurately, the boundary structures such as the leading-edge vortex and its evolution with time need to be resolved with maximum accuracy as they are the primary key to the manifestation of the aperiodic onset. Even a small discrepancy may result in a different dynamical state and lead to an erroneous prediction of the transition route. On the other hand, discrete forcing IBM is known to suffer from non-physical spurious oscillations of the velocity and pressure field near the boundary, which may affect the overall flow-field solution. In this regard, the present work investigates the efficacy of discrete forcing IBM in accurately capturing the transitional dynamics in the flow-field around a plunging elliptic foil by comparing its results with that of a well-validated body-fitted ALE solver.
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TL;DR: The term immersed boundary (IB) method is used to encompass all such methods that simulate viscous flows with immersed (or embedded) boundaries on grids that do not conform to the shape of these boundaries.
Abstract: The term “immersed boundary method” was first used in reference to a method developed by Peskin (1972) to simulate cardiac mechanics and associated blood flow. The distinguishing feature of this method was that the entire simulation was carried out on a Cartesian grid, which did not conform to the geometry of the heart, and a novel procedure was formulated for imposing the effect of the immersed boundary (IB) on the flow. Since Peskin introduced this method, numerous modifications and refinements have been proposed and a number of variants of this approach now exist. In addition, there is another class of methods, usually referred to as “Cartesian grid methods,” which were originally developed for simulating inviscid flows with complex embedded solid boundaries on Cartesian grids (Berger & Aftosmis 1998, Clarke et al. 1986, Zeeuw & Powell 1991). These methods have been extended to simulate unsteady viscous flows (Udaykumar et al. 1996, Ye et al. 1999) and thus have capabilities similar to those of IB methods. In this review, we use the term immersed boundary (IB) method to encompass all such methods that simulate viscous flows with immersed (or embedded) boundaries on grids that do not conform to the shape of these boundaries. Furthermore, this review focuses mainly on IB methods for flows with immersed solid boundaries. Application of these and related methods to problems with liquid-liquid and liquid-gas boundaries was covered in previous reviews by Anderson et al. (1998) and Scardovelli & Zaleski (1999). Consider the simulation of flow past a solid body shown in Figure 1a. The conventional approach to this would employ structured or unstructured grids that conform to the body. Generating these grids proceeds in two sequential steps. First, a surface grid covering the boundaries b is generated. This is then used as a boundary condition to generate a grid in the volume f occupied by the fluid. If a finite-difference method is employed on a structured grid, then the differential form of the governing equations is transformed to a curvilinear coordinate system aligned with the grid lines (Ferziger & Peric 1996). Because the grid conforms to the surface of the body, the transformed equations can then be discretized in the
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TL;DR: In this paper, a new immersed-boundary method for simulating flows over or inside complex geometries is developed by introducing a mass source/sink as well as a momentum forcing.
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TL;DR: In this article, the vortical flow patterns in the wake of a NACA 0012 airfoil pitching at small amplitudes were studied in a low speed water channel, and it was shown that a great deal of control can be exercised on the structure of the wake by the control of the frequency, amplitude and also the shape of the oscillation waveform.
Abstract: The vortical flow patterns in the wake of a NACA 0012 airfoil pitching at small amplitudes are studied in a low speed water channel. it is shown that a great deal of control can be exercised on the structure of the wake by the control of the frequency, amplitude and also the shape of the oscillation waveform. An important observation in this study has been the existence of an axial flow along the cores of the wake vortices. Estimates of the magnitude of the axial flow suggest a linear dependence on the oscillation frequency and amplitude.
672 citations
TL;DR: This article reviews representative numeri- cal methods based on conforming and non-conforming meshes that are currently avail- able for computing fluid-structure interaction problems, with an emphasis on some of the recent developments in the field.
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TL;DR: In this article, the ability of a sinusoidally plunging airfoil to produce thrust, known as the Knoller-Betz or Katzmayr effect, was investigated experimentally and numerically.
Abstract: The ability of a sinusoidally plunging airfoil to produce thrust, known as the Knoller-Betz or Katzmayr effect, is investigated experimentally and numerically. Water-tunnel experiments are performed providing flow visualization and laser Doppler velocimetry data of the unsteady wakes formed by the plunging foils. Vortical structures and time-averaged velocity profiles in the wake are compared with numerical computations from a previously developed inviscid, unsteady panel code that utilizes a nonlinear wake model
408 citations