Direct numerical simulation of the flow around an aerofoil in ramp-up motion

Rosti, Marco E.; Omidyeganeh, Mohammad; Pinelli, Alfredo

doi:10.1063/1.4941529

Cited by 45 publications

(44 citation statements)

References 47 publications

(49 reference statements)

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“…The equations given above, have been made non-dimensional using the magnitude of the free stream velocity U ∞ and the aerofoil chord c. Also, in the momentum Equation 1, Re c = U ∞ c/ν is the chord-based Reynolds number and f i represents a system of singular body forces used to keep into account the presence of the flap as it will be discussed later. The momentum and mass conservation equations (1 and 2), are discretised on a cell-centered, co-located grid using a well-established curvilinear finite volume code [21,33,34]. The fluxes are approximated by a second-order central formulation, and the method of Rhie and Chow [35] is used to avoid spurious pressure oscillations.…”

Section: Numerical Formulationmentioning

confidence: 99%

“…Dumlupinar and Murthy [18] further investigated the performances of various turbulence models and pointed out that different turbulence closures predict a broad range of different behaviours even in light stall cases. Recently, Rosti et al [21] performed a DNS of flow around a NACA0020 aerofoil, with the aim of elucidating the physical mechanisms that determine the dynamic stall vortex creation, its evolution along the aerofoil and the subsequent detachment.…”

Section: Introductionmentioning

confidence: 99%

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Passive control of the flow around unsteady aerofoils using a self-activated deployable flap

Rosti

Omidyeganeh

Pinelli

2017

Journal of Turbulence

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Self-activated feathers are used by many birds to adapt their wing characteristics to the sudden change of flight incidence angle (e.g., sudden increase in angle of attack due to gusts or perching manoeuvres). In particular, dorsal feathers are believed to pop up as a consequence of unsteady flow separation and to interact with the flow to palliate the sudden stall breakdown typical of dynamic stall. Inspired by the adaptive character of birds feathers, some authors have envisaged the potential benefits of using of flexible flaps mounted on aerodynamic surfaces to counteract the negative aerodynamic effects associated with dynamic stall. This contribution explores more in depth the physical mechanisms that play a role in the modification of the unsteady flow field generated by a NACA0020 aerofoil equipped with an elastically mounted flap undergoing a specific ramp-up manoeuvre. It is found that it is possible to design flaps that limit the severity of the dynamic stall breakdown by increasing the value of the lift overshoot also smoothing its abrupt decay in time. A detailed analysis on the modification of the unsteady vorticity field due to the flap flow interaction during the ramp-up motion is also provided to explain the more benign aerodynamic response obtained when the flap is in use.

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Section: Numerical Formulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Passive control of the flow around unsteady aerofoils using a self-activated deployable flap

Rosti

Omidyeganeh

Pinelli

2017

Journal of Turbulence

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“…This literature overview shows the benefits of flaps for a wide range of Reynolds numbers and the potential for technical applications. While the positive effect of the self-adapting mechanism is mentioned in the literature [3,4,8,9,14], there is only one study (by Kernstine et al [4]) of elastic flaps with regard to lift and drag improvements. Because this study focuses on aluminum foil, there is a demand to investigate other elastic materials, since aluminum foil has the disadvantage of plastic deformation, which can be caused by strong gusts.…”

Section: Introductionmentioning

confidence: 99%

Effect of Flexible Flaps on Lift and Drag of Laminar Profile Flow

Reiswich¹,

Finster²,

Heinrich³

et al. 2020

Energies

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Experiments with elastic flaps applied on a common airfoil profile were performed to investigate positive effects on lift and drag coefficients. An NACA0020 profile was mounted on a force balance and placed in a wind tunnel. Elastic flaps were attached in rows at different positions on the upper profile surface. The Reynolds number of the flow based on the chord length of the profile is about 2 × 10 5 . The angle of attack is varied to identify the pre-and post-stall effects of the flaps. Polar diagrams are presented for different flap configurations to compare the effects of the flaps. The results showed that flaps generally increase the drag coefficient due to the additional skin friction and pressure drag. Furthermore, a significant increase of lift in the stall region was observed. The highest efficiency was obtained for the configuration with flaps at the leading and trailing edges of the profile. In this case, the critical angle was delayed and lift was increased in pre-and post-stall regions. This flap configuration was used in a gust simulation in the wind tunnel to model unsteady incoming flow at a critical angle of attack. This investigation showed that the flow separation at the critical angle was prevented. Additionally, smoke-wire experiments were performed for the stall region in order to visualize the flow around the airfoil. The averaged flow field results showed that the leading-edge flaps lean the flow more towards the airfoil surface and reduce the size of the separated region. This reduction improves the airfoil performance in the deep stall region.

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“…4b showing the time evolutions of the lift and drag coefficients obtained by integrating the wall pressure and the shear stress at each time step (mean values: c l = 0.64 and c d = 0.35). From the figure, one can observe the presence of a dominant oscillation period clearly associated to the alternating vortex shedding in the wake, with a corresponding non dimensional frequency, in terms of Strouhal number, equal to S t = f s c / U ∞ ≈ 0.534 [21]. The unsteady behaviour of the spanwise vorticity field, determined by the shear layers instabilities and by the mutual interaction of the vortices embedded in the wake, is the ultimate responsible of the aerodynamic response of the aerofoil to stalled conditions.…”

Section: Baseline Flow Characterisationmentioning

confidence: 99%

Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet

Rosti

Omidyeganeh

Pinelli

2018

Flow Turbulence Combust

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Self-activated feathers are used by almost all birds to adapt their wing characteristics to delay stall or to moderate its adverse effects (e.g., during landing or sudden increase in angle of attack due to gusts). Some of the feathers are believed to pop up as a consequence of flow separation and to interact with the flow and produce beneficial modifications of the unsteady vorticity field. The use of self adaptive flaplets in aircrafts, inspired by birds feathers, requires the understanding of the physical mechanisms leading to the mentioned aerodynamic benefits and the determination of the characteristics of optimal flaps including their size, positioning and ideal fabrication material. In this framework, this numerical study is divided in two parts. Firstly, in a simplified scenario, we determine the main characteristics that render a flap mounted on an aerofoil at high angle of attack able to deliver increased lift and improved aerodynamic efficiency, by varying its length, position and its natural frequency. Later on, a detailed direct numerical simulation analysis is used to understand the origin of the aerodynamic benefits introduced by the flaplet movement induced by the interaction with the flow field. The parametric study that has been carried out, reveals that an optimal flap can deliver a mean lift increase of about 20% on a NACA0020 aerofoil at an incidence of 20o degrees. The results obtained from the direct numerical simulation of the flow field around the aerofoil equipped with the optimal flap at a chord Reynolds number of 2 × 104 shows that the flaplet movement is mainly induced by a cyclic passage of a large recirculation bubble on the aerofoil suction side. In turns, when the flap is pushed downward, the induced plane jet displaces the trailing edge vortices further downstream, away from the wing, moderating the downforce generated by those vortices and regularising the shedding cycle that appears to be much more organised when the optimal flaplet configuration is selected.

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Direct numerical simulation of the flow around an aerofoil in ramp-up motion

Cited by 45 publications

References 47 publications

Passive control of the flow around unsteady aerofoils using a self-activated deployable flap

Passive control of the flow around unsteady aerofoils using a self-activated deployable flap

Effect of Flexible Flaps on Lift and Drag of Laminar Profile Flow

Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet

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