Revisiting Conventional Flaps at High Deflection Rate

Medina, Albert; Ol, Michael V.; Mancini, Peter; Jones, Anya R.

doi:10.2514/1.j055754

Cited by 22 publications

(17 citation statements)

References 18 publications

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“…Nevertheless, Medina et al [17] argued that the transient (unsteady) responses to pulse-like actuators could be better utilized to produce higher lift than the one achieved with periodic forcing, basing these conclusions on an earlier work performed by Amitay and Glezer [18]. Based on these assumptions, a series of experiments to investigate the transient flow responses to low-amplitude high deflection rates of conventional hinged flaps were conducted [17,19]. In order to observe the lift coefficient response to various deflection frequencies, an NACA 0006 airfoil equipped with a TEF (at 50% chord) was tested in a water tunnel, first at 0 • and 20 • AoA [19] and then at a fixed AoA of 20 • , where the 0 • setting corresponds to attached flow, while the 20 • setting represents massively separated flow.…”

Section: Introductionmentioning

confidence: 99%

Near Stall Unsteady Flow Responses to Morphing Flap Deflections

Abdessemed

Yao

Bouferrouk

2021

Fluids

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The unsteady flow characteristics and responses of an NACA 0012 airfoil fitted with a bio-inspired morphing trailing edge flap (TEF) at near-stall angles of attack (AoA) undergoing downward deflections are investigated at a Reynolds number of 0.62 × 106 near stall. An unsteady geometric parametrization and a dynamic meshing scheme are used to drive the morphing motion. The objective is to determine the susceptibility of near-stall flow to a morphing actuation and the viability of rapid downward flap deflection as a control mechanism, including its effect on transient forces and flow field unsteadiness. The dynamic flow responses to downward deflections are studied for a range of morphing frequencies (at a fixed large amplitude), using a high-fidelity, hybrid RANS-LES model. The time histories of the lift and drag coefficient responses exhibit a proportional relationship between the morphing frequency and the slope of response at which these quantities evolve. Interestingly, an overshoot in the drag coefficient is captured, even in quasi-static conditions, however this is not seen in the lift coefficient. Qualitative analysis confirms that an airfoil in near stall conditions is receptive to morphing TEF deflections, and that some similarities triggering the stall exist between downward morphing TEFs and rapid ramp-up type pitching motions.

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Section: Introductionmentioning

confidence: 99%

Near Stall Unsteady Flow Responses to Morphing Flap Deflections

Abdessemed

Yao

Bouferrouk

2021

Fluids

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“…Pure deflection also experiences a gradual shift in lift history phase with increasing reduced frequency k. It should be noted that lift history plots for pure flap deflection are measured from experiment employing zero phase shift φ = 0 • in Eq. (1). Through application of the Theodrosen model, the pure deflection lift histories are of comparable magnitude to those of pure plunge.…”

Section: A Theoretical Approach: Theodorsen's Modelmentioning

confidence: 91%

“…4, this deflection angle presents a nominally attached flow. When engaged in dynamic deflection, the rates of motion considered here are anticipated to support enhanced flow-attachment over the flap [1]. Note that from Eq.…”

Section: A Theoretical Approach: Theodorsen's Modelmentioning

confidence: 95%

“…R ecent parameter studies on transient deflection of fast flaps have shown that immediately upon deflection of the flap, even in a separated flow (the main element being at 20 • incidence), there will be a liftresponse in some proportion to the flap deflection-rate [1]. A simplified analytic model for lift coefficient history, composed of (1) added-mass [2], (2) pitch-rate or virtual camber, and (3) quasi-steady lift from airfoil theory, was moderately successful for transient lift response, but ignored wake-effects.…”

mentioning

confidence: 99%

“…The flap is deflected at the same frequency as the plunge, also sinusoidally, in an attempt to cancel the lift disturbance from plunge. Because the flap frequency and plunge frequency are locked, there is no opportunity to exploit high-lift transients from faster flap deflection [1]. In this study a parameter sweep of the disturbance frequency and amplitude is investigated, and the lift cancellation is informed by both Theodorsen's formula, and an empirical state-space model.…”

mentioning

confidence: 99%

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Lift Disturbance Cancellation with Fast-Flap Actuation

Medina

Hemati

2018

2018 Fluid Dynamics Conference

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Experimental results examining a rapidly-deflecting simple flap of a wall-to-wall NACA 0006 wing in a water tunnel at Re = 40k are presented for a survey of flap deflections designed to negate the lift-transient from an imposed plunge motion of the entire wing. The plunge, over a period ranging from eight convective times to one convective time, is regarded as a vertical disturbance, or a "gust". The flap deflection history is initially derived from Theodorsen's formula for unsteady flap motions, from which one obtains phase and amplitude information. The theoretical derivation makes the standard assumptions of attached flow, planar wake, and no leading edge vortices. Experimental data measurements of lift on the fore-element and the flap of the wing are examined for pure-plunge, for pure flap deflection, and for the combined airfoil plunge and flap deflection motion. The latter shows up to 87% of lift cancellation, verifying the limited, but substantial applicability of Theodorsen's formula. Improvements over the theoretical formulation of lift cancellation are sought by constructing empirical models for both airfoil plunge and flap deflection. The empirical models for airfoil plunge and flap deflection are constructed independent of one another and their superposition is employed to approximate the total lift in combined plunge and deflection motions. It is shown that although the empirical model approach performs similar to the inviscid theory of Theodorsen's model, the empirical model proves more effective in suppressing the leading-edge vortex induced in plunge.

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Inviscid modeling of unsteady morphing airfoils using a discrete-vortex method

Martínez-Carmena,

Ramesh

2023

Theor. Comput. Fluid Dyn.

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A low-order physics-based model to simulate the unsteady flow response to airfoils undergoing large-amplitude variations of the camber is presented in this paper. Potential-flow theory adapted for unsteady airfoils and numerical methods using discrete-vortex elements are combined to obtain rapid predictions of flow behavior and force evolution. To elude the inherent restriction of thin-airfoil theory to small flow disturbances, a time-varying chord line is proposed in this work over which to satisfy the appropriate boundary condition, enabling large deformations of the camber line to be modeled. Computational fluid dynamics simulations are performed to assess the accuracy of the low-order model for a wide range of dynamic trailing-edge flap deflections. By allowing the chord line to rotate with trailing-edge deflections, aerodynamic loads predictions are greatly enhanced as compared to the classical approach where the chord line is fixed. This is especially evident for large-amplitude deformations. Graphical abstract

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Revisiting Conventional Flaps at High Deflection Rate

Cited by 22 publications

References 18 publications

Near Stall Unsteady Flow Responses to Morphing Flap Deflections

Near Stall Unsteady Flow Responses to Morphing Flap Deflections

Lift Disturbance Cancellation with Fast-Flap Actuation

Inviscid modeling of unsteady morphing airfoils using a discrete-vortex method

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