Time resolved PIV analysis of flow over a NACA 0015 airfoil with Gurney flap

Troolin, Dan; Longmire, Ellen; Lai, Wing

doi:10.1007/s00348-006-0143-8

Cited by 70 publications

(30 citation statements)

References 9 publications

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“…Troolin, Longmire & Lai (2006) found that two distinct vortex shedding modes interacted in the wake downstream of the airfoil. The dominant mode resembled Karman vortex shedding behind an asymmetric bluff body, while the second mode related to intermittent shedding of fluid recirculating in the cavity upstream of the Gurney flap.…”

Section: Gurney Flapsmentioning

confidence: 99%

Flow control over an airfoil using virtual Gurney flaps

2015

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Flow control over a NACA 0012 airfoil is carried out using a dielectric barrier discharge (DBD) plasma actuator at the Reynolds number of 20 000. Here, the plasma actuator is placed over the pressure (lower) side of the airfoil near the trailing edge, which produces a wall jet against the free stream. This reverse flow creates a quasi-steady recirculation region, reducing the velocity over the pressure side of the airfoil. On the other hand, the air over the suction (upper) side of the airfoil is drawn by the recirculation, increasing its velocity. Measured phase-averaged vorticity and velocity fields also indicate that the recirculation region created by the plasma actuator over the pressure surface modifies the near-wake dynamics. These flow modifications around the airfoil lead to an increase in the lift coefficient, which is similar to the effect of a mechanical Gurney flap. This configuration of DBD plasma actuators, which is investigated for the first time in this study, is therefore called a virtual Gurney flap. The purpose of this investigation is to understand the mechanism of lift enhancement by virtual Gurney flaps by carefully studying the global flow behaviour over the airfoil. First, the recirculation region draws the air from the suction surface around the trailing edge. The upper shear layer then interacts with the opposite-signed shear layer from the pressure surface, creating a stronger vortex shedding from the airfoil. Secondly, the recirculation region created by a DBD plasma actuator over the pressure surface displaces the positive shear layer away from the airfoil, thereby shifting the near-wake region downwards. The virtual Gurney flap also changes the dynamics of laminar separation bubbles and associated vortical structures by accelerating laminar-to-turbulent transition through the Kelvin-Helmholtz instability mechanism. In particular, the separation point and the start of transition are advanced. The reattachment point also moves upstream with plasma control, although it is slightly delayed at a large angle of attack.

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Section: Gurney Flapsmentioning

confidence: 99%

Flow control over an airfoil using virtual Gurney flaps

2015

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“…This explains a reduction in the vortex formation length behind the Gurney flap. Troolin et al (2006) have pointed that such increase in the net negative vertical velocity on the airfoil wake leads to an enhancement of circulation and thus the lift force.…”

Section: Wake Vortex Dynamicsmentioning

confidence: 99%

Flow control over a NACA 0012 airfoil using dielectric-barrier-discharge plasma actuator with a Gurney flap

et al. 2012

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Flow control study of a NACA 0012 airfoil with a Gurney flap was carried out in a wind tunnel, where it was demonstrated that a dielectric-barrier-discharge (DBD) plasma actuator attached to the flap could increase the lift further, but with a small drag penalty. Timeresolved PIV measurements of the near-wake region indicated that the plasma forcing shifted the wake downwards, reducing its recirculation length. Analysis of wake vortex dynamics suggested that the plasma actuator initially amplified the lower wake shear layer by adding momentum along the downstream surface of the Gurney flap. This enhanced mutual entrainment between the upper and lower wake vortices, leading to an increase in lift on the airfoil.

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“…Based on the study performed by these authors, the time-averaged flow downstream a GF consists of 2 counter-rotating vortices, but the instantaneous flow structure actually consists of a wake of alternately shed vortices. Troolin et al (2006) investigated the wake structure using time-resolved particle image velocimetry. They showed that 2 distinct vortex-shedding modes exist in the wake.…”

Section: Introductionmentioning

confidence: 99%

“…According to the study performed by Date and Turnock (2002), quasi-steady approach has the same prediction of mean performance as time accurate computations. Based on the experimental studies in the literature regarding Gurney-flapped airfoils, the addition of flap originates vortex shedding, and the flow becomes unsteady (Jeffrey et al 2000;Troolin et al 2006). As a result, all computations should be performed in unsteady mode.…”

Section: Introductionmentioning

confidence: 99%

Detailed Numerical Study on the Aerodynamic Behavior of a Gurney Flapped Airfoil in the Ultra-low Reynolds Regime

Khoshlessan¹,

Karimian²

2017

J.Aerosp. Technol. Manag.

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The addition of Gurney flap changes the nature of flow around airfoil by producing asymmetric VonKarman vortex in its wake. Most of the investigations on Gurney flapped airfoils have modeled the flow using a quasisteady approach, resulting in time-averaged values with no information on the unsteady features of the flow. Among these, some investigations have shown that quasi-steady approach does a good job on predicting the aerodynamic coefficients and physics of flow. Previous studies on Gurney flap have shown that the calculated aerodynamic coefficients such as lift and drag coefficients from quasi-steady approach are in good agreement with the time averaged values of these quantities in time accurate computations. However, these investigations were conducted in regimes of medium to high Reynolds numbers where the flow is turbulent. Whether this is true for the regime of ultra-low Reynolds number is open to question. Therefore, it is deemed necessary to examine the previous investigations in the regime of ultra-low Reynolds numbers. The unsteady incompressible laminar flow over a Gurney flapped airfoil is investigated using three approaches; namely unsteady accurate, unsteady inaccurate, and quasisteady. Overall, all the simulations showed that at ultra-low Reynolds numbers quasi-steady solution does not necessarily have the same correlation with the time averaged results over the unsteady accurate solution. In addition, it was observed that results of unsteady inaccurate approach with very small time steps can be used to predict time-averaged quantities fairly accurate with less computational cost.

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Time resolved PIV analysis of flow over a NACA 0015 airfoil with Gurney flap

Cited by 70 publications

References 9 publications

Flow control over an airfoil using virtual Gurney flaps

Flow control over an airfoil using virtual Gurney flaps

Flow control over a NACA 0012 airfoil using dielectric-barrier-discharge plasma actuator with a Gurney flap

Detailed Numerical Study on the Aerodynamic Behavior of a Gurney Flapped Airfoil in the Ultra-low Reynolds Regime

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