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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24 Feb 2010
TL;DR: In this article, Computational Fluid Dynamics methods are used to resolve the flow around two-and three-dimensional flapping foils and wings, at the scale relevant to insect flight, move at large rotation angles, which is difficult to handle in existing mesh motion solvers.
Abstract: Both biological and engineering scientist have always been intrigued by the flight of insects and birds. For a long time, the aerodynamic mechanism behind flapping insect flight was a complete mystery. Recently, several experimental and numerical flow visualisations were performed to investigate the aerodynamics around flapping wings. Flapping wings produce both lifting and propulsive forces such that it becomes possible for insects and smaller bird species, e.g. hummingbirds, to stay aloft and hover, but also to perform extreme manoeuvres. Because of this versatility, insects and smaller birds are an inspiration for the development of flapping wing Micro Air Vehicles, small man-made flyer's to use in exploration and surveillance. In this thesis, Computational Fluid Dynamics methods are used to resolve the flow around two- and three-dimensional flapping foils and wings. Flapping wings, at the scale relevant to insect flight, move at large rotation angles, which is difficult to handle in existing mesh motion solvers. Therefore, existing methods to deform the mesh have been compared and improved. A relatively new method is implemented, based on the interpolation of radial basis functions. Using the mesh motion based on radial basis function interpolation, the flow around flapping airfoils and wings at hovering and forward flight conditions has been investigated. The forces and vortex patterns have been studied, especially the influence of wing kinematics on the leading-edge vortex. In addition, preliminary results are described of the effects by active wing flexing.
45 citations
TL;DR: In this paper, a discrete vortex method to simulate the separated flow around an aerofoil undergoing pitching motion is described, where vorticity generated in the thin layer around the body is discretized into vortices in accordance with themultipanel surface representation by convectionand diffusion.
Abstract: Amodi® ed discrete vortexmethod to simulate the separated ow around an aerofoil undergoingpitchingmotion is described The vorticity generated in the thin layer around the body is discretized into vortices in accordance with themultipanel surface representation By convectionand diffusion the vortices are released from the body and advanced in the wake as determined by the Biot± Savart law and random-walkmodel, respectively Both unsteady static and pitching cases are presented, and comparisonwith the test data illustrates that, without prior knowledge of the developing separation and reattachment points for the model, good agreement has been achieved
35 citations
TL;DR: An iterative approach to compute the forcing term implicitly is proposed, which reduces the errors at the boundary and retains the stability guarantees of the original semi-implicit discretization of the Navier–Stokes equations.
30 citations