Oscillation Frequency and Amplitude Effects on the Wake of a Plunging Airfoil

Young, John; Lai, Joseph H.K.

doi:10.2514/1.5070

Cited by 244 publications

(144 citation statements)

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“…A common experimental and computational model of flapping flight is the sinusoidal pitching and/or heaving motion of an airfoil geometry in which an LEV is generated, and the effects of lift and drag can be carefully documented. Many experiments have looked at symmetric airfoils in sinusoidal heaving motion [11,12], or pitching motion [13], finding the boundary layer separation and formation of a LEV can greatly impact the lift generation. Experiments by Cleaver et.…”

Section: Introductionmentioning

confidence: 99%

Unsteady high-lift mechanisms from heaving flat plate simulations

Franck

Breuer

2017

International Journal of Heat and Fluid Flow

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Flapping animal flight is often modeled as a combined pitching and heaving motion in order to investigate the unsteady flow structures and resulting forces that could augment the animal's lift and propulsive capabilities. This work isolates the heaving motion of flapping flight in order to numerically investigate the flow physics at a Reynolds number of 40,000, a regime typical for large birds and bats and challenging to simulate due to the added complexity of laminar to turbulent transition in which boundary layer separation and reattachment are traditionally more difficult to predict. Periodic heaving of a thin flat plate at fixed angles of attacks of 1, 5, 9, 13, and 18 degrees are simulated using a large-eddy simulation (LES). The heaving motion significantly increases the average lift compared with the steady flow, and also surpasses the quasi-steady predictions due to the formation of a leading edge vortex (LEV) that persists well into the static stall region. The progression of the high-lift mechanisms throughout the heaving cycle is presented over the range of angles of attack. Lift enhancement compared with the equivalent steady state flow was found to be up to 17% greater, and up to 24% greater than that predicted by a quasi-steady analysis. For the range of kinematics explored it is found that maximum lift enhancement occurs at an angle of attack of 13 degrees, with a maximum lift coefficient of 2.1, a mean lift coefficient of 1.04.

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Section: Introductionmentioning

confidence: 99%

Unsteady high-lift mechanisms from heaving flat plate simulations

Franck

Breuer

2017

International Journal of Heat and Fluid Flow

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“…Extensive experimental and computational studies have been carried out to understand the unsteady aerodynamics of flapping wings [4][5][6]. However, in most of these studies, the effects of flow fluctuations on the flapping flight are ignored by considering a uniform flow condition.…”

Section: Introductionmentioning

confidence: 99%

Stochastic Bifurcation Analysis of an Elastically Mounted Flapping Airfoil

2018

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Abstract. The present paper investigates the effects of noisy flow fluctuations on the fluid-structure interaction (FSI) behaviour of a span-wise flexible wing modelled as a two degree-of-freedom elastically mounted flapping airfoil. In the sterile flow conditions, the system undergoes a Hopf bifurcation as the free-stream velocity exceeds a critical limit resulting in a stable limit-cycle oscillation (LCO) from a fixed point response. On the other hand, the qualitative dynamics changes from a stochastic fixed point to a random LCO through an intermittent state in the presence of irregular flow fluctuations. The probability density function depicts the most probable system state in the phase space. A phenomenological bifurcation (P-bifurcation) analysis based on the transition in the topology associated with the structure of the joint probability density function (pdf) of the response variables has been carried out. The joint pdf corresponding to the stochastic fixed point possesses a Dirac delta function like structure with a sharp single peak around zero. As the mean flow speed crosses the critical value, the joint pdf bifurcates to a crater-like structure indicating the occurrence of a P-bifurcation. The intermittent state is characterized by the co-existence of the unimodal as well as the crater like structure.

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“…Motion of the airfoil is introduced by a combination of rigid-body motion and deformation of the grid, resulting in time-dependent grid metrics and Jacobian. Details of the method may be found in Young and Lai [1,3], and Tuncer and Platzer [5]. Versions of the code have been parallelized with OpenMP for use on an Alpha cluster, and Parallel Virtual Machine (PVM) for use on a cluster of Pentiumbased workstations running Linux.…”

Section: Methodsmentioning

confidence: 99%

“…The Navier Stokes solver has been validated against a number of flow visualizations for pure plunging motion, and quantitative experimental and computational studies of pure pitching motion, with good results [1]. Here combined pitching and plunging motions are computed, with thrust and efficiency results compared to small-amplitude potential theory (Garrick [2]), largeamplitude unsteady panel method (UPM) potential flow simulations [1,3], and experimental results of Anderson et al [4].…”

Section: Introductionmentioning

confidence: 99%