選択的シーディングLDAによる乱流間欠性の研究 : 第1報,条件付乱流域平均の直接測定

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 nonturbulent fluid is entrained into the turbulent zone, 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 particle are measured. Therefore, the turbulent zone averages are obtained directly. This paper describes and 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 LDA processed with a frequency counter, and they proved to coincide with the values secured by means of conditional averaging of HWA signals.
社団法人日本機械学会の論文
1989-03-25