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

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Publisher
Springer Vienna
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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