Passive scalar intermittency in low temperature helium flows

Abstract

We report new measurements of turbulent mixing of temperature fluctuations in a low temperature helium gas experiment, spanning a range of microscale Reynolds number, $R_{\lambda }$, from 100 to 650. The exponents ${\xi }_n$ of the temperature structure functions $<|\theta (x+r)-\theta (x){|}^n>\sim r^{{\xi }_n}$ are shown to saturate to ${\xi }_{\infty }\simeq 1.45\pm 0.1$ for the highest orders, $n\sim 10$. This saturation is a signature of statistics dominated by front-like structures, the cliffs. Statistics of the cliff characteristics are performed, particularly their width are shown to scale as the Kolmogorov length scale.

4 pages, with 4 figures