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, $R_λ$, from 100 to 650. The exponents $ξ_{n}$ of the temperature structure functions $<|θ(x+r)-θ(x)|^n > \sim r^{ξ_{n}}$ are shown to saturate to $ξ_{\infty} \simeq 1.45 \pm 0.1$ 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.