周期撹乱が二次元混合層の乱流遷移に及ぼす影響

抄録

The laminar-turbulent transition of a mixing layer excited by oscillating flat plates at an exit of a two-dimensional nozzle was experimentally investigated. The mixing layer was formed between the jet issued from the nozzle and the surrounding quiescent fluid. The plates oscillated vertically in relation to the mean flow. Upper and lower flat plates oscillated symmetrically. The oscillation frequency, 5 Hz, was two orders of magnitude smaller than the fundamental frequency of the velocity fluctuation in the natural transition process. The amplitude of the respective plates was 0.5, 1.0, 1.5, 2.0 and 3.0 mm. Mean and fluctuating velocity components in the streamwise and normal directions were measured by hot-wire anemometers. We examine how this localized perturbation influences the turbulent transition of the mixing layer. The phase variation of the flow rate at the exit of the nozzle increased as the plate amplitude increased, though they were not in a proportional relationship. The mean velocity profiles skewed at the exit of the nozzle with the large amplitude, though the skewness disappeared downstream. The mean vorticity thickness was thick with large amplitude. The irregular fluctuation velocity with large amplitude increased earlier, and the turbulent transition was accelerated.