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MEASUREMENT OF FINE SCALE STRUCTURE IN TURBULENCE BY QUAD-PLANE STEREOSCOPIC PIV

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To investigate fine scale structure of turbulent flows, quad-plane stereoscopic particle image velocimetry (QPSPIV) has been developed. QPSPIV provides three-dimensional distribution of three components of velocity and nine components of velocity gradient with a high spatial resolution. The QPSPIV system was applied to measurements in a turbulent jet for two different conditions: Reλ = 76.8 and 128.9. Probability density functions (PDFs) of velocity gradients agree with DNS data. Fine scale structures of turbulence are investigated based on an eddy identification scheme used for the analysis of DNS data which requires full velocity gradient tensor. PDFs of the diameter and maximum azimuthal velocity of the detected eddies show peaks at D/η ≈ 8 and uθ,max/uk ≈ 1.5 for both Reynolds numbers, and this coincides with the results obtained from DNS. The present study gives experimental evidence of the existence of the coherent fine scale eddy in turbulence.

Author(s):

Yoshitsugu Naka    
Tokyo Institute of Technology
Japan

Kenichi Tomita    
Tokyo Institute of Technology
Japan

Masayasu Shimura    
Tokyo Institute of Technology
Japan

Naoya Fukushima    
Tokyo Institute of Technology
Japan

Mamoru Tanahashi    
Tokyo Institute of Technology
Japan

Toshio Miyauchi    
Tokyo Institute of Technology
Japan