Turbulence measurements in axisymmetric jets of air and helium. Part 1. Air jet

TLDR

A turbulent round jet of air discharging into quiescent air was studied experimentally. The study measured velocity fluctuation moments up to fourth order to characterize turbulent transport and evaluate models for triple moments in Reynolds stress equations. The authors used ×‑wire hot‑wire probes on a moving shuttle to eliminate rectification errors and measured velocity fluctuation moments up to fourth order. Fourth moments matched quasi‑Gaussian predictions across the jet, third‑moment profiles differed from earlier data with negative values near the axis, the basic triple‑moment model was inadequate, but including mean‑strain production and rapid pressure correlations yielded satisfactory predictions in the fully turbulent region, and momentum flux matched nozzle input within ±5% while radial diffusive flux of turbulent kinetic energy was near zero.

Abstract

A turbulent round jet of air discharging into quiescent air was studied experimentally. Some × -wire hot-wire probes mounted on a moving shuttle were used to eliminate rectification errors due to flow reversals in the intermittent region of the jet. Moments of velocity fluctuations up to fourth order were measured to characterize turbulent transport in the jet and to evaluate current models for triple moments that occur in the Reynolds stress equations. Fourth moments were very well described in terms of second moments by the quasi-Gaussian approximation across the entire jet including the intermittent region. Profiles of third moments were found to be significantly different from earlier measurements: 〈 uv 2 〉, 〈 uw 2 〉 and 〈 u 2 v 〉 are found to be negative near the axis of the jet. The Basic triple moment model that included turbulent production and models for the dissipation and the return-to-isotropy part of the pressure correlations was found to be unsatisfactory. When mean-strain production and a model for rapid pressure correlations were also included, predictions were satisfactory in the fully turbulent region. The consistency of the measurements with the equations of motion was assessed: momentum flux across the jet was found to be within ±5% of the nozzle input and the integral of radial diffusive flux of turbulent kinetic energy across the jet calculated from the measured third moments was found to be close to zero.