LDV Measurements ｉｎ Two-Dimensional　Bent-over Jets (Part 1) -Mean flow properties and curvature effects on turbulence structures of nonbuoyant jets?

摘要

An experimental study of two-dimensional bent-over nonbuoyant jets which are characterized by streamline curvature is reported. The experimental data include mean and turbulent flow properties obtained from measurement of instantaneous velocity and temperature in the flow. The experiments were conducted in a hydroulic flume using Laser Doppler Velocimetry (LDV) and resistance thermometry. The mean flow properties studied are trajectories of the jets, mexing rate, velocity and temperature distributions. In the turbulent hw studies, the effects of streamline curvature on turbulence structure were investigated. There, turbulence intensities, Reynolds stress, intermittency and turbulent spectra are calculated. The measurements extended over the near-to-intermediate field, namely y/D＜60, where y is the distance along the flume and D is the width of the jet at the exit. In spite of the presence of strong streamline curvature, streamwise mean velocity distributions are found to be nearly Gaussian when scaled properly. The trajectory of the maximum velocity point scales with length scale based on the kinematic momentum flux and follows a half power law. Even if the buoyancy effects are absent, it is rather difficult to isolate the curvature effects from the combined effects of curvature and nonequilibrium in the outer portion of the curved jets. However, the stabilizing effects of curvature in the inner portion and the destabilizing effects in the outer portion can be clearly seen from an isotropy parameter of the urbulent fluctuations and the temperature fluctuations.