Investigations of an Airfoil at Low Reynolds Number Conditions

Brehm, Christoph; Mack, Steffen; Groß, Andreas; Fasel, Hermann F.

doi:10.2514/6.2008-3765

Cited by 26 publications

(14 citation statements)

References 27 publications

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“…Our earlier experimental and numerical campaign [2,3] indicated that a considerable improvement of aerodynamic performance using active flow control could be expected for α=8.64° and Re C =64,200. For this particular case, using our compressible finite-volume code, we investigated active flow control by pulsed vortex generator jets (VGJs) and a plasma actuator.…”

Section: Dns Of Entire Airfoilmentioning

confidence: 96%

“…A comparison with earlier lift and drag data is shown in Figure 11. The earlier CFD results by Brehm et al [3] were obtained with the same code on a computational grid with identical wall-normal and circumferential grid resolution but half the number of grid cells in the spanwise direction. The thin straight line that connects the linear lift region near α=−5° with the "plateau region" near 10°<α<15° approximately coincides with the lift curve of the experiment in which the flow was artificially transitioned.…”

Section: Controlled Flowmentioning

confidence: 97%

“…However, successful scaled flight research can only be guaranteed if the geometrically scaled model exhibits the same aerodynamics as the full size wing (aerodynamic scaling) [1] . For example, in both experiments [2] and numerical investigations [3] , it was found that at low angles-of-attack, the boundary layer separates in the aft section of the blade. This separation results in a considerably reduced slope (based on thin airfoil theory) of the lift curve (see Figure 2).…”

Section: Introductionmentioning

confidence: 96%

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Control of Boundary-Layer Separation for Lifting Surfaces

Balzer

Groß

Fasel

2009

2009 DoD High Performance Computing Modernization Program Users Group Conference

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The lack of understanding of most of the relevant physical mechanisms when applying flow control limits the prospects of successfully transitioning flow-control technologies into real flight vehicles. Successful control of boundary-layer separation for lifting surfaces promises major performance gains especially when large laminar runs are desired in order to minimize the skin-friction drag.We systematically explore the fundamental mechanisms of the interaction of separation and transition that are relevant for effective and efficient flow control applications.Toward this end, we are employing computational fluid dynamics (CFD) for investigating active flow control for a NACA 64 3 -618 airfoil at a chord Reynolds number Re C =64,200 and various angles-of-attack. CFD results are compared to wind/water tunnel experiments carried out at the University of Arizona. For simulations of the entire wing section we are using a high-order-accurate finite volume code based on the compressible NavierStokes equations. For very highly resolved DNS which focus exclusively on the separated region on the suction side of the wing, we are employing a higher-orderaccurate compact finite difference code based on the incompressible Navier-Stokes equations in vorticityvelocity formulation. These simulations are set up to fully resolve the flow field and enable us to reveal some of the intricate physical mechanisms associated with unsteady separation and transition, flow instabilities, and active flow control.

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Section: Dns Of Entire Airfoilmentioning

confidence: 96%

Section: Controlled Flowmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 96%

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Control of Boundary-Layer Separation for Lifting Surfaces

Balzer

Groß

Fasel

2009

2009 DoD High Performance Computing Modernization Program Users Group Conference

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“…The shear-layer (KelvinHelmholtz) instability produces spanwise "rollers" which facilitate transition and provide necessary wall-normal momentum exchange which closes the bubble and reattaches the flow. 4 Figure 4(c) shows the oil flow visualization of the baseline flow at α = 16°. Laminar separation is evident at x/c ≈ 0.02.…”

Section: A Baseline Flowmentioning

confidence: 97%

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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“…Foundation of studying complex laminar separation phenomena around the airfoil at low Reynolds number started from laminar separation bubble model [2] (long and short separation bubble) which More and more numerical simulation supports this view [10,11,[13][14][15] .…”

mentioning

confidence: 97%

Evolution of the Non-linear and Unsteady Low Reynolds Number Laminar Separation Bubble around the Airfoil with Small angle of attack

Bai

Liu

et al. 2016

46th AIAA Fluid Dynamics Conference

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Laminar separation bubble and laminar separation are the typical characteristics of the low speed low Reynolds number flow. There are stronger unsteady and nonlinear effects as the Reynolds number decreasing. Three significant effects are listed below: 1 Decreasing of the lift coefficients, increasing of the drag coefficients, and rapid deterioration of the lift-to-drag ratio. 2 Nonlinear phenomenon of aerodynamic coefficients near the small angle of attack. 3 Static hysteresis effect at the middle angle of attack. Based on the former numerical simulation studies about the laminar separation effect around the E387 and SD8020 airfoil at the low Reynolds number, the author discovered a new kind of trailing-edge laminar separation bubble(TLSB), which is significantly different from the classical long laminar separation bubble(LLSB). Furthermore, in this paper, the unsteady numerical method and wind tunnel PIV flow visualization method were taken to study the flow field of the symmetrical airfoil SD8020 at the small angle of attack with low Reynolds number more deeply and systemically.The unsteady and time-averaged flowfield structure and pressure coefficient, the nonlinear alteration of the unsteady lift coefficient with the angle to attack were given out in this paper. The results of CFD and experiments were good agreement with each other, especially for the Strouhal number (St), proved that our studies were correct.The PIV experiment proved that the classical long laminar separation is the time-averaged results of the unsteady laminar separation flow field. And the time-averaged trailing-edge laminar separation bubble indeed exists. And there are significant differences between the TLSB and LLSB among the shape, inner structure and the evolution law. The details of the time-averaged structures of the two LSBs were given out in this paper. The St number and the amplitude of the lift coefficients pulse between the two LSBs change sharply. And the unsteady and time-averaged pressure distributions and separation flows of the two LSBs are different greatly. The nonlinear effects of the lift coefficients to the angle of attack are caused by the evolutions between the TLSB and the LLSB.

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Investigations of an Airfoil at Low Reynolds Number Conditions

Cited by 26 publications

References 27 publications

Control of Boundary-Layer Separation for Lifting Surfaces

Control of Boundary-Layer Separation for Lifting Surfaces

Pulsed Blowing on a Laminar Airfoil at Low Reynolds Number

Evolution of the Non-linear and Unsteady Low Reynolds Number Laminar Separation Bubble around the Airfoil with Small angle of attack

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