Experimental Investigation of Dissipation Element Statistics in a Jet Flow

摘要

We present a detailed experimental investigation of conditional statistics related to dissipation elements based on the scalar field θ and its scalar dissipation rate χ. Based on high frequency two-dimensional measurements of the mass fraction of propane in a turbulent round jet discharging into surrounding air, we acquire data resolving the Kolmogorov scale in every spatial direction using a high-speed Rayleigh scattering technique and Taylor's hypothesis. The Reynolds number (based on nozzle diameter and jet exit velocity) varies between 2,000 and 6,700 and the Schmidt number between 1.2 and 1.7. The experimental results for the normalized marginal pdf P(l) of the length of dissipation elements follow closely the theoretical model derived by Wang and Peters (J. Fluid. Mech. 608:113-138, 2008). We also find that the mean linear distance between two extreme points of an element is of the order of the Taylor microscale λ. Furthermore, the conditional mean (Δθ|l) scales with Kolmogorov's 1/3 power.