乱流間欠性研究へのレーザドップラ流速計の応用

概要

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A novel method to measure the conditional turbulent zone averages in a fully developed jet is demonstrated. In conventional methods to study the turbulent intermittency, hot wire signals are processed to detect the turbulent zone and then the conditional average velocities are obtained. But this signal processing is cumbersome and difficult to set the threshold of turbulence without ambiguity. In a jet flow, the surrounding non-turbulent fluid is entrained into the turbulent zoze, but the reverse process never occurs. Therefore small particles seeded in the nozzle flow remain only in the turbulent zone. By means of a laser doppler anemometer (LDA), the velocities of these particles are measured, therefore, the turbulent zone averages are obtained directly. This paper describes an experimental comparison of this method with the conventional one. A circular air jet seeded with DOP particles was blown into a seedless coflowing stream. Then the mean velocities and the turbulent intensities were measured by a LDA processed with a frequency counter, and they were proved to coincide with the values secured by means of conditional average of HWA signals. Furthermore, a seedless jet in a seeded co flowing stream was measured, and the effects of selective seeding on the mean velocities and the turbulent intensities were examined to understand the entrainment and the turbulent mixing process of jet.
九州大学の論文
1988-06-30