R. Bhaskaran et Ap. Rothmayer, SEPARATION AND INSTABILITIES IN THE VISCOUS-FLOW OVER AIRFOIL LEADINGEDGES, Computers & fluids, 27(8), 1998, pp. 903-921
The two-dimensional, unsteady, leading-edge flow over stationary, pitc
hing and oscillating airfoils is studied using the Navier-Stokes equat
ions for flow past a parabola. Grid-converged solutions have been obta
ined for the initial stages of unsteady separation for impulsively-sta
rted unsteady flow and for pitch-up at constant rate. The results comp
are favorably with corresponding full-airfoil computations. It is show
n that small perturbations in the flow can generate eddies in the boun
dary layer before how reversal occurs in the base flow. Oscillations a
ppear in the skin friction which grow in amplitude and convect downstr
eam with time. Above a certain amplitude, the skin Friction becomes ne
gative locally, giving rise to small recirculating eddies. This type o
f eddy creation prior to reversal in the base flow is in general agree
ment with the theory of Rayleigh instabilities. The wavelength of thes
e instabilities scales as Re-0.43 which is in reasonable agreement wit
h the theoretical value of Re-1/2 for the Rayleigh instability. (C) 19
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