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research-article

Dynamic Stall Flow Structure and Forces on Symmetrical Airfoils at High Angles of Attack and Rotation Rates

[+] Author and Article Information
Ryan Leknys

The University of Adelaide, Adelaide, South Australia, 5006
ryan.leknys@adelaide.edu.au

Maziar Arjomandi

The University of Adelaide, Adelaide, South Australia, 5006
maziar.arjomandi@adelaide.edu.au

Richard Kelso

The University of Adelaide, Adelaide, South Australia, 5006
richard.kelso@adelaide.edu.au

Cristian Birzer

The University of Adelaide, Adelaide, South Australia, 5006
cristian.birzer@adelaide.edu.au

1Corresponding author.

ASME doi:10.1115/1.4041523 History: Received January 11, 2018; Revised September 07, 2018

Abstract

This article describes a direct comparison between two symmetrical airfoils undergoing dynamic stall at high, unsteady reduced frequencies under otherwise identical conditions. Particle image velocimetry was performed to distinguish the differences in flow structure between a NACA 0021 and a NACA 0012 airfoil undergoing dynamic stall. In addition, surface pressure measurements were performed to evaluate aerodynamic load and investigate the effect of laminar separation bubbles and vortex structures on the pressure fields surrounding the airfoils. Airfoil geometry is shown to have a significant effect on flow structure development and boundary layer separation, with separation occurring earlier for thinner airfoil sections undergoing constant pitch-rate motion all reduced frequencies. Inertial forces were identified to have a considerable impact on the overall force generation with increasing rotation rate. Force oscillation was observed to correlate with multiple vortex structures shedding at the trailing edge during high rotation rates. The presence of laminar separation bubbles on the upper and lower surfaces were shown to dramatically influence the steady-state lift of both airfoils. Post-stall characteristics are shown to be independent of airfoil geometry such that periodic vortex shedding was observed for all cases. However, the onset of deep stall is delayed with increased non-dimensional pitch rate due to the delay in initial dynamic-stall vortex.

Copyright (c) 2018 by ASME
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