Abstract

Three dimensional tomographic time dependent PIV measurements of high Reynolds number (Re= u’.L/ν) laboratory turbulence (N. Worth at CUED ) are presented which show the existence of long-lived, highly sheared thin layer eddy structures with thickness of the order of the Taylor microscale and internal fluctuations. Similar intermittent highly sheared layer structures are also observed in direct numerical simulations of Ishihara et al (2014) (in Nagoya) at higher values of Re, with a comparable layer thickness λ (of order L Re-1/2 ). Outside these layers the cascade of small eddies are distorted as they impact and transfer net energy into the layers –there is also some up-scale transfer as well. Within these ‘spaghetti-sandwich‘ layers intense elongated vortices form, with the usual Kolmogorov micro- scale L Re-3/4, where there is intense dissipation (of order L/λ times the average value ε) and velocity fluctuations of order u’- which is not consistent with the overall non-intermittent Kolmogorov-Obukhov (1941) statistical model. The intense shear layers are of practical significance in decorrelating regions of large scale eddying and through the influence of their intense internal microscale substructures on particle motions and combustion. Ref: Hunt JCR , T. Ishihara, N. Worth, Y. Kaneda (2014) Thin shear layers in high Reynolds number turbulence-tomographic experiments and a local distortion model. J. Flow Turb Comb vol. 92, no 3, pp607-650 (on-line DoI 10.1007)