Experimental study of boundary-layer transition on an airfoil induced by periodically passing wake |
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Authors: | W-P Jeon T-C Park S-H Kang |
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Institution: | (1) Center for Turbulence and Flow Control Research Institute of Advanced Machinery and Design Seoul National University, Seoul 151-742, Korea e-mail: wpjeon@plaza1.snu.ac.kr, KR;(2) School of Mechanical and Aerospace Engineering Seoul National University, Seoul 151-742, Korea, KR |
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Abstract: | Hot-wire measurements are performed in boundary-layer flows developing on a NACA 0012 airfoil over which wakes pass periodically.
The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The time-
and phase-averaged mean streamwise velocities and turbulence fluctuations are measured to investigate the phenomena of wake-induced
transition. Especially, the phase-averaged wall shear stresses are evaluated using a computational Preston tube method. The
passing wakes significantly change the pressure distribution on the airfoil, which has influence on the transition process
of the boundary layer. The orientation of the passing wake alters the pressure distribution in a different manner. Due to
the passing wake, the turbulent patches are generated inside the laminar boundary layer on the airfoil, and the boundary layer
becomes temporarily transitional. The patches propagate downstream at a speed smaller than the free-stream velocity and merge
together further downstream. Relatively high values of phase-averaged turbulence fluctuations in the outer part of the boundary
layer indicate the possibility that breakdown occurs in the outer layer away from the wall. It is confirmed that the phase-averaged
mean velocity profile has two dips in the outer region of the transitional boundary layer for each passing cycle.
Received: 12 February 2001 / Accepted: 6 July 2001 Published online: 23 November 2001 |
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