The evolution of a turbulent isothermal jet in a uniform turbulent external coflow

Abstract

An experimental investigation is presented that examines the effects of external turbulence on the development and evolution of a turbulent isothermal coflowing jet. Three intensities of external turbulence, two different jet model diameters, and two initial jet velocities were combined to obtain data for twelve different experimental conditions. The measured instantaneous velocity data resulting from these experiments were statistically processed to obtain mean velocities, Reynolds normal and shear stresses, integral length scales, and energy spectra both within the jet and in the external flow. The experimental results indicate that the presence of external turbulence begins to affect the development of a jet in the range of 15 to 25 momentum radii downstream from the jet exit by enhancing the diffusion of jet momentum.

A new entrainment velocity function is developed for use in an integral model to predict the effects of external turbulence on the evolution of a coflowing jet. The resulting predictions are compared with experimental data and yield accurate predictions for the radial spread and velocity decay for a jet in a laminar external coflow while yielding relatively good agreement for a jet in a turbulent external coflow.