Active Flow Control for NACA 6-Series Airfoil at Re = 64,200

Groß, Andreas; Fasel, Hermann F.

doi:10.2514/1.j050051

Cited by 33 publications

(32 citation statements)

References 17 publications

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“…At AR=0.8 the normalized maximum difference is around 0.02, which is more than one order larger than that of AR=0.4 and reflects the strong spanwise non-uniformity. The inaccurate prediction of the leading edge separation line using a small aspect ratio has also been 505 observed by Gross & Fasel [1]. They found a spanwise straight separation line in their DNS study using AR=0.2, while the comparative experiment with AR=4.0 shows a curved separation line [69].…”

Section: A C C E P T E D Mmentioning

confidence: 63%

“…Comparisons between experimental and numerical studies have shown that for flow past bluff bodies, the spanwise coherence of the vortices may be artificially reinforced 15 in 2D simulations [1] and thus the validity of such results is questionable. In 3D simulations the spanwise domain size, representing the separation distance between end plates in experiments or the length of the bluff body in simulations, is normalized and represented by the aspect ratio AR=L z /L re f , where L z is the spanwise domain size and L re f is a reference length (cylinder diameter D or airfoil chord length C, etc.).…”

Section: A C C E P T E D Mmentioning

confidence: 99%

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Assessment of spanwise domain size effect on the transitional flow past an airfoil

Zhang

Samtaney

2016

Computers & Fluids

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Please cite this article as: Wei Zhang, Ravi Samtaney, Assessment of spanwise domain size effect on the transitional flow past an airfoil, Computers and Fluids (2015), doi: 10.1016/j.compfluid.2015 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPTA C C E P T E D M A N U S C R I P T Highlights• DNS on the separated-transitional-reattached flow past the airfoil.• The effects of the spanwise domain size are analyzed from various aspects.• The spanwise domain size has significant effects on the various turbulent statistics.• Small spanwise domain size tends to underpredict the spanwise variations.• Examination through only a few quantities may lead to misleading conclusion.

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Section: A C C E P T E D Mmentioning

confidence: 63%

Section: A C C E P T E D Mmentioning

confidence: 99%

Assessment of spanwise domain size effect on the transitional flow past an airfoil

Zhang

Samtaney

2016

Computers & Fluids

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“…As a result, the surface curvature is discontinuous at the junctions between the actuator exit and the airfoil surface. In the present study, the SJ is simply modeled by the time-periodic velocity boundary conditions at the actuator exit, [11][12][13]18,24 instead of a cavity-type actuator where the jet is realized by the piston stroke in the cavity. 17,20,33,38 Although phase lag exists between the piston velocity and the jet velocity, 23 and the jet will undergo viscous dissipation, we mainly focus on the effects of jet on flow separation control and neglect the implementation details of a synthetic jet.…”

Section: A Physical Setupmentioning

confidence: 99%

“…In most DNS and LES studies at relatively higher Reynolds number, the spanwise domain size is normally chosen as L z = 0.1-0.2C. 11,12,38,40 In the DNS study by Hoarau et al…”

Section: A Physical Setupmentioning

confidence: 99%

“…Separation is alleviated through the mechanism of energizing the flow in the boundary layer, either by directly injecting high-momentum fluid through blowing or by introducing high-momentum fluid from the exterior cross-flow through suction. The pulsed jet [10][11][12][13] is similar to the steady blowing but differs in that the jet is injected into the boundary layer periodically. The boundary layer flow is sufficiently excited that perturbations amplify and transition to turbulence is initiated.…”

Section: Introductionmentioning

confidence: 99%

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A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil

Zhang

Samtaney

2015

Physics of Fluids

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CitationA direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil 2015, 27 (5) We present results of direct numerical simulations of a synthetic jet (SJ) based separation control of flow past a NACA-0018 (National Advisory Committee for Aeronautics) airfoil, at 10• angle of attack and Reynolds number 10 4 based on the airfoil chord length C and uniform inflow velocity U 0 . The actuator of the SJ is modeled as a spanwise slot on the airfoil leeward surface and is placed just upstream of the leading edge separation position of the uncontrolled flow. The momentum coefficient of the SJ is chosen at a small value 2.13 × 10 −4 normalized by that of the inflow. Three forcing frequencies are chosen for the present investigation: the low frequency (LF) F + = f e C/U 0 = 0.5, the medium frequency (MF) F + = 1.0, and the high frequency (HF) F + = 4.0. We quantify the effects of forcing frequency for each case on the separation control and related vortex dynamics patterns. The simulations are performed using an energy conservative fourth-order parallel code. Numerical results reveal that the geometric variation introduced by the actuator has negligible effects on the mean flow field and the leading edge separation pattern; thus, the separation control effects are attributed to the SJ. The aerodynamic performances of the airfoil, characterized by lift and lift-to-drag ratio, are improved for all controlled cases, with the F + = 1.0 case being the optimal one. The flow in the shear layer close to the actuator is locked to the jet, while in the wake this lock-in is maintained for the MF case but suppressed by the increasing turbulent fluctuations in the LF and HF cases. The vortex evolution downstream of the actuator presents two modes depending on the frequency: the vortex fragmentation and merging mode in the LF case where the vortex formed due to the SJ breaks up into several vortices and the latter merge as convecting downstream; the discrete vortices mode in the HF case where discrete vortices form and convect downstream without any fragmentation and merging. In the MF case, the vortex dynamics is at a transition state between the two modes. The low frequency actuation has the highest momentum rate during the blowing phase and substantially affects the flow upstream of the actuator and triggers early transition to turbulence. In the LF case, the transverse velocity has a 1%U 0 pulsation at the position 18%C upstream of the actuator. C 2015 AIP Publishing LLC.

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Numerical investigation of rotational augmentation for S822 wind turbine airfoil

et al. 2012

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Direct numerical simulations were carried out for an S822 wind turbine blade section at a chord Reynolds number of Re D 100;000 and an angle of attack of˛D 5°. Results for a stationary non-rotating blade section compare favorably with wind tunnel data by the University of Illinois at Urbana-Champaign and XFoil predictions. By adding volume forcing terms to the right-hand side of the Navier-Stokes equations, the Coriolis and centrifugal accelerations resulting from blade rotation are modeled in the blade section simulations. Blade rotation is shown to delay separation especially near the hub, resulting in a lift increase of up to 100% and a drag reduction. The simulations provide insight into a physical mechanism that offers an explanation for the lift increase observed for rotating blade sections when compared with stationary blade sections, which is commonly referred to as rotational augmentation. Rotation is shown to lead to a radial velocity component toward the blade tip in areas where the velocity is substantially different from its free-stream value, such as near the stagnation point and especially in the separated flow region, and to the appearance of stationary and traveling crossflow vortices. A linear stability theory analysis that compares favorably with the simulation data provides proof that the primary instabilities are of a mixed type, including both a two-dimensional mode (Tollmien-Schlichting and Kelvin-Helmholtz type) and a stationary and unsteady crossflow mode. The crossflow instabilities accelerate transition, leading to separation delay, lift increase and drag reduction. This effect is very pronounced at 20% blade radius and still present at 80% radius. Because periodicity conditions were applied in the spanwise direction, the present results provide an explanation for rotational augmentation that is not based on the transfer of fluid from the inboard region toward the blade tip ('centrifugal pumping'). For the low Reynolds number conditions considered here, crossflow instabilities, which destabilize the flow leading to earlier transition and a separation delay, may contribute to rotational augmentation.Accurate blade performance predictions are crucially needed during wind turbine development. A survey of numerical methods for analysing the aerodynamic and aeroelastic properties of wind turbines was provided by Hansen et al. 1 Blade element momentum theory (BEMT) is one of the main tools for computing the performance of entire turbines. This approach was found to perform well for attached flow conditions but underestimate the stall onset and hence the peak power output when two-dimensional (2D) airfoil data are used that are not corrected for rotational effects. For example, the National Renewable Energy Laboratory (NREL) Combined Experiment (Phase II) turbine power exceeded predictions by approximately 15-20%. 2 Almost all research suggests that this effect can be attributed to stall delay caused by blade rotation. 3The survey paper by Leishman et al. 4 points out that many details of the...

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Active Flow Control for NACA 6-Series Airfoil at Re = 64,200

Cited by 33 publications

References 17 publications

Assessment of spanwise domain size effect on the transitional flow past an airfoil

Assessment of spanwise domain size effect on the transitional flow past an airfoil

A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil

Numerical investigation of rotational augmentation for S822 wind turbine airfoil

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