Experimental Investigation of Open- and Closed-Loop Control for Airfoil Under Low Reynolds Number Conditions

Plogmann, Benjamin; Mack, Steffen; Fasel, Hermann F.

doi:10.2514/6.2009-4282

Cited by 32 publications

(22 citation statements)

References 12 publications

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“…Apparently, the receptivity of the boundary layer to this disturbance has a frequency preference near 40 Hz (f+ ≈ 1). This agrees well with Plogmann et al 22 , who found that when actuating from near the leading edge of the NACA 64 3 -618 at α > 10°, forcing at f+ = 0.88 was found to be the most effective in increasing the maximum lift.…”

Section: B Steady Vs Pulsed Blowingsupporting

confidence: 89%

Pulsed Blowing on a Laminar Airfoil at Low Reynolds Number

Packard

Bons

2011

29th AIAA Applied Aerodynamics Conference

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The range of effectiveness of pulsed actuation with varying frequency, duty cycle and blowing ratio is explored on a NACA 64 3 -618 airfoil at a Reynolds number of 6.4x10 4 . Pulsed blowing from a row of discrete holes located at five percent chord on the upper surface of the airfoil successfully reduces separation over a wide range of reduced frequency (0.1-1), blowing ratio (0.5-2), and duty cycle (0.6-50%). A phase-locked investigation, by way of particle image velocimetry, at ten degrees angle of attack illuminates physical mechanisms responsible for separation control of pulsed actuation at a low frequency and duty cycle. Temporal resolution of large structure formation and wake shedding is obtained, revealing a key mechanism for separation control. The Kelvin-Helmholtz instability is identified as responsible for the formation of smaller structures in the separation region which produce favorable momentum transfer, assisting in further thinning the separation region and then fully attaching the boundary layer. The proximity to the wall dampens the Kelvin-Helmholtz instability, leaving no further evidence until the proceeding jet perturbation arrives. Nomenclaturelocal -P s, ∞ ) / (P T, ∞ -P s, ∞ )] C µ = jet momentum coefficient [see Eq. (1)] c = chord d = diameter of actuator and pressure tap holes DC = actuation duty cycle f = actuation frequency f s = shear layer shedding frequency f+ = reduced frequency (fc/U ∞ ) n = wall normal distance from airfoil surface N = number of actuation holes P = pressure Re = Reynolds number based on airfoil chord (U ∞ c/v) S = planform area Sr θs = Strouhal number based on conditions at the point of separation (f s θ s /U es ) T = actuation period t = time elapsed from beginning of actuation waveform U ∞ = freestream velocity U es = boundary layer edge velocity at the separation location x = chordwise coordinate y = wall normal distance α = airfoil angle of attack θ s = momentum thickness at the separation location ν = kinematic viscosity

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Section: B Steady Vs Pulsed Blowingsupporting

confidence: 89%

Pulsed Blowing on a Laminar Airfoil at Low Reynolds Number

Packard

Bons

2011

29th AIAA Applied Aerodynamics Conference

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“…Computational work by Brehm et al 6 show that wall-normal slot blowing and suction prove more effective when forced near the leading edge than when the actuator is placed more aft on the airfoil, just ahead of the separation point. Results of Plogmann et al 3 also show more effective control in leading edge actuation, particularly at higher angles of attack. They speculate that at high angles of attack, actuation too far downstream of the leading edge will be largely ineffective, or will require an impractical amount of energy as the actuator lies in the region of fully separated flow.…”

Section: Introductionmentioning

confidence: 80%

“…Some passive methods, like boundary layer trips 1,2 , are effective in delaying or preventing flow separation in some flight environments, but can produce undesirable results in conditions for which they were not designed. Active flow control methods such as plasma actuators 3 , fluidic oscillators 4 , pulsed jets, and acoustics 5 are beneficial in that they can be activated only when necessary; however, the energy required to be effective must be carefully considered.…”

Section: Introductionmentioning

confidence: 99%

Effect of Spanwise Jet Spacing on Separation Control for Swept and Unswept Airfoils

Walker

Hipp

Benton

et al. 2015

33rd AIAA Applied Aerodynamics Conference

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The performance of active flow control on a NACA 64 3 -618 laminar wing at an effective streamwise Reynolds number of 64,000 with and without sweep (Λ = 30° and 0°) is evaluated at post-stall angles of attack. Actuation is implemented near the leading edge using discrete, wall-normal, steady vortex generating jets (VGJs). The effect of increasing spanwise distance between jets along the leading edge of the wing is studied. For the swept wing configuration, lift coefficient shows a strong dependence on the number of vortex generating jets distributed near the leading edge. While holding blowing ratio constant and increasing spanwise jet spacing, small performance gains are noted while significantly reducing the required mass flow across a wide range of angles of attack (22º ≤ α ≤ 35º). While holding the total mass flow rate constant and increasing the spanwise distance between jets, significant performance gains are seen. The controlled straight wing configuration demonstrated a similar trend with increased spanwise jet spacing, but only over a narrow range of angle of attack (centered at α = 18º). Above this threshold, the flow displays a tendency toward multiple stable states in a seemingly unpredictable manner. Nomenclature b = span of wing [m] BR= jet blowing ratio, BR = U jet / U edge C l = airfoil section lift coefficient,pressure [Pa] Re c = chordwise Reynolds number, Re c = U eff c / ν Re eff = effective streamwise Reynolds number, Re eff = U ∞ c eff / ν U ∞ = freestream velocity [m/s] U eff = effective freestream velocity [m/s], U ∞ cos(Λ) c = chord [m] c eff = effective chord [m], c eff = c / cos(Λ) d = jet diameter [m] N jets = number of jets x = leading edge-normal coordinate [m] y = wall-normal coordinate [m] z = spanwise coordinate [m] α = airfoil angle of attack [°] Λ = wing sweep angle [°] 2 Subscripts edge = local boundary layer edge eff = effective variable measurement jet = jet exit max = maximum value of variable ps = pressure surface of wing ss = suction surface of wing ∞ = freestream

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“…Examples are separation control for low-pressure turbine blades 1-3 and laminar airfoils. [4][5][6][7] In this paper the question is addressed if harmonic blowing through a slot is also effective at higher Reynolds numbers. The Reynolds number scalability of a flow control strategy can be investigated by keeping an appropriate dimensionless parameter (such as the momentum coefficient) constant and then determining how dimensionless performance parameters (such as the lift and drag coefficient) change when the Reynolds number is altered (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Two-dimensional (2-D) wing sections were tested in the wind and water tunnel for Reynolds numbers between 64,200 and Re=322,000, the model (1/5 scale) cruise Reynolds number based on MAC. 5,6,9 The experiments were complemented by simulations for Re=64,200 4, 10 and Re=322,000. 11,12 The full size cruise Reynolds number is 3.2million.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of Separation Control for Wing Sections

Groß

Fasel

2012

6th AIAA Flow Control Conference

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Numerical simulations of the unsteady separated flow over wing sections at flight Reynolds numbers are challenging. Direct numerical simulations which resolve all scales of the fluid motion promise the highest degree of fidelity but are computationally very expensive. Even large-eddy simulations can be prohibitively expensive because of the high grid resolution required near the walls. Hybrid turbulence models employ Reynolds-averaged NavierStokes near the walls and adjust the turbulence model contribution away from the walls according to the local physical grid resolution. In this paper hybrid simulations based on a one-equation renormalization group model are presented for a modified NACA643-618 airfoil at a chord Reynolds number of 1 million and for 10, 20, and 30 degrees angle of attack. For these conditions a short laminar separation bubble develops near the leading edge and the flow separates turbulent from the suction side downstream of the leading edge bubble. For 10 degrees angle of attack the lift and drag data obtained from the simulations are in good agreement with XFoil predictions and active flow control by harmonic blowing through a spanwise slot upstream of the turbulent separation is investigated.

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Experimental Investigation of Open- and Closed-Loop Control for Airfoil Under Low Reynolds Number Conditions

Cited by 32 publications

References 12 publications

Pulsed Blowing on a Laminar Airfoil at Low Reynolds Number

Pulsed Blowing on a Laminar Airfoil at Low Reynolds Number

Effect of Spanwise Jet Spacing on Separation Control for Swept and Unswept Airfoils

Numerical Investigation of Separation Control for Wing Sections

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