Statistical Characteristics of the Cross-Sectional Concentration Field in a Round Counter Jet

Abstract

The concentration field of a diffusing matter in the cross plane of a turbulent round jet injected into a counter-flowing uniform stream has been investigated using the PLIF technique. In order to capture images in good focus from a camera oriented obliquely to the object plane, the camera configuration has been designed according to the Scheimpflug condition and a water prism has been introduced to reduce the amount of radial distortions that are caused by capturing images through a channel wall. In addition to the mean and rms concentration fields in the cross-section, turbulent dispersion properties, such as the centroid and the absolute and relative spreads, have been examined by integrating the instantaneous concentration field over a cross-sectional area. It has been confirmed that a random fluctuation in the centroid of instantaneous concentration field exists in the cross plane and its amplitude increases downstream more rapidly as compared with the conventional jet in a quiescent ambient. These results could have a close relation with a radial oscillation of the jet core, which is expected to be responsible for its enhanced mixing efficiency.