The applicability of the Kutta condition for a heaving airfoil was experimentally investigated, using flow visualization and Laser Doppler and Hot-film anemometry. The visualized stream lines at the trailing edge show, in some cases, momentary turning around it, which implies that the Kutta condition does not hold at least locally. The flow pattern about 1/8 chord length downstream shows a thin velocity shear layer, that is, a vortex layer, which closely follows the trace of the trailing edge of the heaving airfoil. The flow pattern obtained by the linearized potential theory also gives the similar feature. The strength of the vortex layer and its phase relation agree fairly well each other for low reduced frequency, although these agreements become poor for higher one, where the linearization assumption is also violated. This vortex layer grows wider and eventually rolls up far downstream for the reduced frequency larger than 1.3, or simply decays out after several wavy motions for the lower one than it, which were found in visualized flow field and by Hot-film survey of the wake field of the oscillating airfoil. Throughout this experiment, the computerized flow measuring system was extensively utilized.
<論文>振動翼後流の実験
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