Active Flow Control at Low Reynolds Numbers by Periodic Airfoil Morphing

Jones, Gareth R.; Santer, Matthew; Papadakis, George; Debiasi, Marco

doi:10.2514/6.2016-1303

Cited by 4 publications

(1 citation statement)

References 13 publications

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“…In some of these studies, the periodic excitations were prescribed as standing waves. Jones et al [12] experimentally studied standing-wave morphing at a Reynolds number of Re = 50, 000 for a variety of temporal frequencies and angles of attack. The authors found increased velocity within the time-averaged boundary layer for certain morphing frequencies, and an associated increase in mean lift and reduction in mean drag.…”

Section: Introductionmentioning

confidence: 99%

Surface morphing for aerodynamic flows at low and stalled angles of attack

Thompson¹,

Goza²

2021

Preprint

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In the current work we numerically study the effect of traveling-wave surface morphing actuation, which is a lightweight, spatially distributed actuation strategy made possible by advances in materials science. Although this actuation strategy has been studied at higher Reynolds numbers for an airfoil and a rectangular flat plate, its effects at low Reynolds numbers relevant to microair vehicles have not yet been investigated. We perform high-fidelity 2D numerical simulations to study the effects of traveling wave surface morphing on the suction surface of NACA0012 at Re = 1,000. The kinematics of actuation are defined by wavenumber and wavespeed, both of which are varied over a wide range of values to include parameters that considerably change the lift dynamics as well as those that do not. We first study the effect of actuation at an angle of attack of α = 5 • , where the unactuated flow is steady. The lift dynamics are found to align with the surface morphing kinematics, and there is a low-pressure minimum shown to be introduced into the flow-field by morphing that advects at a speed agnostic to the morphing parameters. Lift benefits are found to be maximal when the morphing kinematics align with this intrinsic flow speed. We then investigate the role of morphing in the presence of an unsteady, separated baseline flow (with intrinsic vortex-shedding processes) at α = 15 • . At this higher angle of attack, we identify three distinct behavioral regimes based on the relationship between morphing and the underlying shedding frequency. Of these regimes, the most beneficial to mean lift is the lock-on regime, where the vortex-shedding dynamics align with the morphing kinematics. Lock-on was similarly found using this actuation strategy at higher Reynolds numbers, though in that setting the effect was to reduce separation, whereas at these lower Reynolds numbers the outcome is that vortex shedding persists with-in certain cases-significant lift benefits. We also identify other regimes where morphing can become out of phase with the vortex-shedding dynamics, termed here the interactive regime, and where morphing leaves the unactuated dynamics unaltered, termed here the superposition regime. At the higher angle of attack, parameters leading to lift benefits/detriments are explained in terms of the effect of morphing on the leading and trailing-edge vortex. Where appropriate, connections between the mechanisms at the higher angle of attack are drawn to the matching/disparity of timescales between morphing and lift-producing pressure signatures seen in the lower-angle-of-attack setting.

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Section: Introductionmentioning

confidence: 99%