Numerical simulations of dynamic stall phenomena around an airfoil oscillating in a coupled mode, in which the pitching and heaving oscillations have some phase difference, have been performed with a Navier ‐Stokes code. The propulsive efe ciency and the thrust have been calculated for various combinations of the phase difference and the reduced frequency for two different amplitude ratios. The effects of the dynamic stall phenomena on the behaviors of the propulsive efe ciency and thrust are discussed in detail by examination of each e ow pattern obtained. Highest efe ciency has been observed for the case in which the pitching oscillation advances 90 deg ahead of the heaving oscillation and the reduced frequency is at some optimum value, for which there appears no appreciable e ow separation in spite of large-amplitude oscillations. For phase angles and reduced frequency other than thisbestcondition, efe ciency israpidly degraded by theoccurrenceof thelarge-scaleleading-edgeseparation.
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Isogai et al. (1999) studied this question.
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