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

Influence of a back-flow flap on the dynamic stall flow topology 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png CEAS Aeronautical Journal Springer Journals

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

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

CEAS Aeronaut J (2018) 9:39–51 https://doi.org/10.1007/s13272-017-0274-z OR IGINAL PAPER Influence of a back-flow flap on the dynamic stall flow topology 1 1 1,2 3 • • • C. C. Wolf A. D. Gardner C. B. Merz S. Opitz Received: 2 February 2017 / Revised: 7 September 2017 / Accepted: 23 October 2017 / Published online: 13 November 2017 Deutsches Zentrum fu ¨ r Luft- und Raumfahrt e.V. 2017 Abstract Dynamic stall is a major concern for highly Keywords Helicopter rotor  Wind tunnel  Flow control loaded helicopter rotors in fast forward flight. The potential Dynamic stall  Experiment of a back-flow flap for dynamic stall reduction is investi- gated. The flap assembly is mounted on the suction side of List of symbols a helicopter main rotor-blade airfoil undergoing deep-stall a Temporal POD coefficient pitch oscillations. Wind-tunnel experiments using high- c Airfoil model chord (m) speed particle image velocimetry were conducted to iden- C Drag coefficient tify the flow topology and to investigate the flap’s method C Lift coefficient of operation. A phase-averaged proper orthogonal decom- C Pitching moment coefficient position (POD) is used to identify relevant flow events and C Pressure coefficient to compare test cases with and without flap. The evolution f Frequency of pitching (Hz) of the large-scale dynamic stall vortex in the initial phases k Reduced frequency, k ¼ pfc=V of flow separation is analyzed in detail. The back-flow flap m POD mode number splits the vortex into two smaller vortices and thereby M Mach number reduces the pitching-moment peak. This effect can be N Number of samples described through the eigenmode coefficients of the POD. N Reduced-order cut-off The study closes with an analysis of different pitching Re Reynolds number based on c frequencies, which do not affect the flap’s method of t Time (s) operation. u, w Velocity in x direction and z direction (m/s) u Vector of 2-D...
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Publisher
Springer Journals
Copyright
Copyright © 2017 by Deutsches Zentrum für Luft- und Raumfahrt e.V.
Subject
Engineering; Aerospace Technology and Astronautics
ISSN
1869-5582
eISSN
1869-5590
D.O.I.
10.1007/s13272-017-0274-z
Publisher site
See Article on Publisher Site

Abstract

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.

Journal

CEAS Aeronautical JournalSpringer Journals

Published: Nov 13, 2017

References

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