Numerical Investigations of a Back-Flow Flap for Dynamic Stall Control

Kaufmann, Kurt; Gardner, Anthony Donald; Richter, Kai

doi:10.1007/978-3-319-03158-3_26

Cited by 5 publications

(7 citation statements)

References 5 publications

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“…Computations using the DLR-Tau URANS code using the method of Kaufman et al [36] were performed to estimate the correct size and position of the flap. This 2D method uses a flap (Fig.…”

Section: Design Of the Experiments 21 Auxiliary Cfd Airfoil Computationsmentioning

confidence: 99%

“…The flap angle is measured by Hall-effect sensors and is factored Fig. 2 Grid geometry for the CFD design computations [36] Fig. 3 Comparison of predicted peak integrated force changes with flow control using DLR-TAU, for different flap lengths and positions for the deep stall case equivalent to a = 22 ± 8 at k ¼ 0:06. a C Lmax , b C Mmin into the force computation.…”

Section: Airfoil Section Designmentioning

confidence: 99%

“…The pressure integration on the airfoil included sensors above and below the flap. The pressure under the flap was taken to be a constant from the single pressure sensor present there, as a constant pressure was indicated by the CFD computations of [36]. Figure 5b shows a top-view of the airfoil with the flap.…”

Section: Airfoil Section Designmentioning

confidence: 99%

“…The suitability of back-flow flaps for dynamic stall suppression was first postulated by Höfinger [35], and influencing the dynamic stall using an active back-flow flap was investigated as part of the DLR project STELAR. Initial investigations using CFD indicated that a reduction of the pitching moment peak of the order of 25-35% could be achieved [36]. Further investigations showed that actuating the flap passively might not work as hoped [37], and using this background, a glove for an existing wind-tunnel model was designed with a solid-state hinge, a magnetic actuator system and straps to limit the flap opening angle to 30 [37,38].…”

Section: Introductionmentioning

confidence: 99%

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Reduction of dynamic stall using a back-flow flap

Gardner¹,

Opitz²,

Wolf³

et al. 2017

CEAS Aeronaut J

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A back-flow flap attached to the suction side of an airfoil is investigated in both passively and actively actuated modes for the control of dynamic stall. This method of dynamic stall control has low power requirements and no parasitic drag when not actuated. Experiments in a low-speed wind tunnel at 50 m/s were used to characterize the reduction in dynamic stall hysteresis using pressure measurements on the midline airfoil section. It was found that the pitching moment peak is reduced by an average of 25% for all deep stall test cases for active actuation of the flap, while for passive actuation the pitching moment peak is reduced by 19%. In each case the maximum lift remained the same, while the peak drag increased by an average of 2.5% for the active flap, and by 0.9% for the passive flap. With the flap closed at low angles of attack, the reference values of the airfoil are retained. KeywordsHelicopter blade Á Wind tunnel Á Flow control Á Dynamic stall Á Back-flow flap Á Experiment List of symbols a; a max Angle of attack; maximum ( ) c Airfoil model chord (m) C D ; C D max Drag coefficient; peak C L ; C L max Lift coefficient; peak C M ; C M min Pitching moment coefficient; peak C P Pressure coefficient f Frequency of pitching (Hz) M Mach number k Reduced frequency: k ¼ pfc=v 1 Re Reynolds number based on c t Time (s) T Period (s) u, v Velocity: in x direction, in z direction (m/s) v 1Freestream velocity (m/s) x, zCoordinates: chord, upward (m)This paper is based on a presentation at the AHS 72nd Annual Forum,

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“…Computations using the DLR-Tau URANS code using the method of Kaufman et al [36] were performed to estimate the correct size and position of the flap. This 2D method uses a flap (Fig.…”

Section: Design Of the Experiments 21 Auxiliary Cfd Airfoil Computationsmentioning

confidence: 99%

Section: Airfoil Section Designmentioning

confidence: 99%

Section: Airfoil Section Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Reduction of dynamic stall using a back-flow flap

Gardner¹,

Opitz²,

Wolf³

et al. 2017

CEAS Aeronaut J

Self Cite

View full text Add to dashboard Cite

show abstract

“…The basic concept was patent-registered by Höfinger [15]. A numerical study was performed to estimate possible gains of the flap and to optimize its geometrical parameters, see Kaufmann et al [16]. If the back-flow flap is attached to the suction side of the airfoil in a distance of 0.4 chord lengths to the leading edge, and deployed during dynamic stall, it will split up the large-scale stall vortex.…”

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confidence: 99%

Influence of a back-flow flap on the dynamic stall flow topology

et al. 2017

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Dynamic stall is a major concern for highly loaded helicopter rotors in fast forward flight. The potential of a back-flow flap for dynamic stall reduction is investigated. The flap assembly is mounted on the suction side of a helicopter main rotor-blade airfoil undergoing deep-stall pitch oscillations. Wind-tunnel experiments using high-speed particle image velocimetry were conducted to identify the flow topology and to investigate the flap's method of operation. A phase-averaged proper orthogonal decomposition (POD) is used to identify relevant flow events and to compare test cases with and without flap. The evolution of the large-scale dynamic stall vortex in the initial phases of flow separation is analyzed in detail. The back-flow flap splits the vortex into two smaller vortices and thereby reduces the pitching moment peak. This effect can be described through the eigenmode coefficients of the POD. The study closes with an analysis of different pitching frequencies, which do not affect the flap's method of operation.

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