The laminar-turbulent transition of a mixing layer induced by oscillating flat plates at an exit of a two-dimensional nozzle was experimentally investigated. The mixing layer was formed between the jet, which issued from the nozzle and the surrounding quiescent fluid. The plates oscillated vertically in relation to the mean flow. The oscillation frequency was two orders of magnitude smaller than the fundamental frequency of the velocity fluctuation. Mean and fluctuating velocity components in the streamwise and normal directions were measured by hot-wire anemometers. In the oscillating state, the same phenomenon as in the natural transition process appeared more upstream. In the early stage within the nonlinear region, the growth of fluctuating velocity attenuated and the Reynolds shear stress component decreased. The decrease in their production rate due to the expansion of the mixing layer contributed to the attenuation and decrease. The probability of the streamwise and normal fluctuating velocity components taking the same sign, increased or decreased in accordance with the increase and decrease of the Reynolds shear stress component. The randomness factor, which had been proposed by Sato, appeared to be a reasonable indicator of the present transition process, especially in the process in which the periodic velocity fluctuation became irregular. However, this factor certainly indicated the same value at two streamwise positions.

These results indicate that effective improvement of image quality can be expected with interpolation. Thus, image quality and the ability to depict images can be improved while maintaining the present acquisition time and image quality. In addition, this can be achieved more effectively than at present even if the acquisition time is reduced.

The laminar-turbulent transition of a mixing layer induced by oscillating flat plates at the exit of a two-dimensional nozzle was experimentally investigated. The mixing layer was formed between the jet, which issued from the nozzle, and the surrounding quiescent fluid. The plates oscillated vertically in relation to the jet. The oscillation frequency was two orders of magnitude smaller than the fundamental frequency of the fluctuating velocity. The oscillating amplitude was double that of a previous report. The oscillating frequency was pseudo-steady and the same as in the previous report, at 5 Hz, and unsteady at 15 Hz. Mean and fluctuating velocity components in the streamwise and normal directions were measured by hot-wire anemometers. As the flow proceeds downstream, the mixing layer entrains the surrounding quiescent fluid. This entrainment is affected by the oscillating frequency rather than the oscillating amplitude. The variation of the streamwise velocity with the oscillating phase is much affected by the oscillating amplitude rather than the oscillating frequency. On the other hand, the variation of the normal velocity is affected by both oscillating amplitude and frequency. For an irregularly fluctuating velocity, a linear region where the velocity grows exponentially first exists. The spatial growth rate in this region is the same between the streamwise and normal components, and does not differ with various oscillating amplitudes and frequencies.

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