Numerical investigations on flow structure and behavior of vortices in the dynamic stall of an oscillating pitching hydrofoil

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 (PIV) 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. 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 was shown to dramatically influence the steady-state lift of both airfoils. Poststall 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 nondimensional pitch rate due to the delay in initial dynamic-stall vortex.

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Numerical Investigations of Dynamic Stall on a Rotor with Cyclic Pitch Control

Journal of the American Helicopter Society ◽

10.4050/jahs.64.012007 ◽

2019 ◽

Vol 64 (1) ◽

pp. 1-14 ◽

Cited By ~ 4

Author(s):

Johannes Letzgus ◽

Anthony D. Gardner ◽

Till Schwermer ◽

Manuel Keßler ◽

Ewald Krämer

Keyword(s):

Dynamic Stall ◽

Pitch Control ◽

Numerical Investigations

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Numerical investigations of flow structure in gas turbine shroud gap

Journal of Physics Conference Series ◽

10.1088/1742-6596/760/1/012039 ◽

2016 ◽

Vol 760 ◽

pp. 012039

Author(s):

F Wasilczuk ◽

P Flaszyński ◽

P Doerffer

Keyword(s):

Gas Turbine ◽

Flow Structure ◽

Numerical Investigations

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Comparison Between NACA 65 Profile and Circular Arc Blade Based on Numerical Investigation

Volume 1C, Symposia: Gas-Liquid Two-Phase Flows; Gas and Liquid-Solid Two-Phase Flows; Numerical Methods for Multiphase Flow; Turbulent Flows: Issues and Perspectives; Flow Applications in Aerospace; Fluid Power; Bio-Inspired Fluid Mechanics; Flow Manipulation and Active Control; Fundamental Issues and Perspectives in Fluid Mechanics; Transport Phenomena in Energy Conversion From Clean and Sustainable Resources; Transport Phenomena in Materials Processing and Manufacturing Processes ◽

10.1115/fedsm2017-69014 ◽

2017 ◽

Author(s):

Tao Bian ◽

Qianpeng Han ◽

Martin Böhle

Keyword(s):

Flow Structure ◽

Lower Cost ◽

Flow Behavior ◽

Axial Flow ◽

Leading Edge ◽

Circular Arc ◽

Spacing Ratio ◽

Flow Loss ◽

The Difference ◽

And Behavior

For the axial flow fans NACA profiles have been well explored. However, the development and production of NACA profiles are also very expensive. Due to their lower cost of production circular arc blades are also applied to axial flow fans. But there is few information in the open literature focusing on flow loss and behavior of circular arc blades. Therefore, one question remains: how much is the difference of flow loss and behavior between NACA profiles and circular arc blades. In this paper NACA 65 profile and circular arc blade are examined by numerical method. The paper shows the flow loss of both blades in dependence of incidence, Reynolds number and spacing ratio. The occurrence of flow behavior, such as separation bubbles on the leading edge and flow structure on the sidewall is examined and discussed. The flow structure is given on basis of numerical flow picture. Additionally, the flow loss in the sidewall region of both investigated blades are worked out and compared.

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