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Journal of Flow Visualization and Image Processing
SJR: 0.161 SNIP: 0.312 CiteScore™: 0.1

ISSN Print: 1065-3090
ISSN Online: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.2018026747
pages 1-13

INSIGHT INTO COHERENCE STRUCTURE IN LOGARITHMIC REGION OF WALL TURBULENCE WITH DETACHED EDDY BY USING CONDITIONALLY AVERAGED TWO-CAMERA PIV MEASUREMENTS

Yasuo Hattori
Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba, 270-1194, Japan
Hitoshi Suto
Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-city, Chiba, 270-1194, Japan
Keisuke Nakao
Central Research Laboratory, Mitsubishi Electric Corp., Amagasaki C., Hyogo, Japan; Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-city, Chiba, Japan
Hiromaru Hirakuchi
Fluid Dynamics Sector, Central Research Institute of Electric Power Industry (CRIEPI) 1646 Abiko, Abiko-shi, Chiba 270-1194, Japan

ABSTRACT

Two-camera particle image velocimetry (PIV) was used to investigate the structural characteristics of organized motions in a logarithmic layer under influences of overlying detached eddies, which mimics very-large-scale motions in the near-neutral atmospheric surface layer. We used the same experimental technique of our previous studies, except for velocity measurements: in the present study, the velocity vectors were measured with a two-camera PIV technique to ensure spatial fine resolutions for capturing turbulence vortices and also a large visualized area for observing organized motions. Two-dimensional velocity fields in a streamwise-spanwise plane of the logarithmic layer were visualized by light sheets discharged from yttrium aluminum garnet (YAG) laser systems. Visualized images were captured by CCD cameras, and then velocity vectors were calculated with a cross-correlation method. After confirming the existence of large-scale structures with the spatial distributions of two-point correlations of streamwise-velocity fluctuations, which showed long tails of high-correlation regions in the streamwise direction, we detected the snapshots including the organized motions by using time-series data of higher-order moments obtained by a spatial averaging procedure for velocity vectors in each snapshot. The organized motions accompanied by streaky structures of low-momentum motions, the characteristic length of which fully exceeded the logarithmic layer height in the streamwise direction, meandered in the spanwise direction, and such motions generated large streamwise-velocity fluctuations in low-frequency regions through velocity gradient in the spanwise direction.