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Unsteady RANS Simulations of Strong and Weak 3D Stall Cells on a 2D Pitching Aerofoil

1
School of Water, Energy and Environment, Cranfield University, Bedfordshire MK43 0AL, UK
2
Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK
*
Author to whom correspondence should be addressed.
Fluids 2019, 4(1), 40; https://doi.org/10.3390/fluids4010040
Received: 29 January 2019 / Revised: 22 February 2019 / Accepted: 26 February 2019 / Published: 2 March 2019
(This article belongs to the Special Issue Turbulence and Transitional Modeling of Aerodynamic Flows)
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Abstract

A series of three-dimensional unsteady Reynolds-averaged Navier–Stokes (RANS) simulations are conducted to investigate the formation of stall cells over a pitching NACA 0012 aerofoil. Periodic boundary conditions are applied to the spanwise ends of the computational domain. Several different pitching ranges and frequencies are adopted. The influence of the pitching range and frequency on the lift coefficient (CL) hysteresis loop and the development of leading-edge vortex (LEV) agrees with earlier studies in the literature. Depending on pitching range and frequency, the flow structures on the suction side of the aerofoil can be categorized into three types: (i) strong oscillatory stall cells resembling what are often observed on a static aerofoil; (ii) weak stall cells which are smaller in size and less oscillatory; and (iii) no stall cells at all (i.e., flow remains two-dimensional) or only very weak oval-shaped structures that have little impact on CL. A clear difference in CL during the flow reattachment stage is observed between the cases with strong stall cells and with weak stall cells. For the cases with strong stall cells, arch-shaped flow structures are observed above the aerofoil. They resemble the Π-shaped vortices often observed over a pitching finite aspect ratio wing. View Full-Text
Keywords: pitching aerofoil; unsteady RANS; hysteresis loop; leading-edge vortex; stall cells pitching aerofoil; unsteady RANS; hysteresis loop; leading-edge vortex; stall cells
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Liu, D.; Nishino, T. Unsteady RANS Simulations of Strong and Weak 3D Stall Cells on a 2D Pitching Aerofoil. Fluids 2019, 4, 40.

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