MEASUREMENTS OF TURBULENCE CHARACTERISTICS IN VARIOUS FLOW FIELDS BY MEANS OF PIV AND LDA

摘要

Turbulence characteristics in several flow fields are compared between measurement data acquired by means of laser Doppler anemometer (LDA) and particle image velocimetry (PIV). The PIV is effective to understand the spatial distributions of the turbulence characteristics and can directly measure the integral length scales from spatial correlation coefficients. However, in general, PIV has less time resolution than LDA. In other words, it presumes that there are differences in the data meanings obtained by LDA or PIV. It is important to clarify the differences in measurement techniques of PIV and LDA to understand the turbulence characteristics. In the LDA measurement, two point simultaneous acquisitions of velocities are necessary to measure the integral length scale directly without applying the Taylor's hypothesis. Therefore this study is carried out by means of PIV and two LDA systems composed by He-Ne and Ar ion lasers. Analyzed flows in this report are grid turbulence, flows around a circular cylinder and a rectangular cube. In the all experiments, the results acquired by the PIV and the LDA were compared with each other about the mean velocities, turbulence intensities, spatial correlations and integral length scales. In addition, the validities of integral length scale calculated by using Taylor's hypothesis are evaluated and the convection velocities of vortex are discussed in the flows.