MEASUREMENTS OF FLUID PARTICLE CORRELATED MOTION IN THE FAR-FIELD OF AN AXISYMMETRICAL JET/

Typical features of fluid-particle interaction in the far field of an axisymmetric polydispersed particle laden tube jet were measured and a nalysed in the present study. Measurements up to 45 jet diameters were obtained by using a phase Doppler anemometer. The statistical propert ies of four particle size classes were obtained in order to cover a wi de range of particle relaxation times. The downstream evolution of the mean longitudinal particle velocity field and of the particle radial and longitudinal turbulent components is first displayed. We show that a Stokes number based on the time scale of the large ''structural'' e ddies is a relevant parameter to describe the selective influence of t he jet flow on the particle mean velocity field. The anisotropy betwee n axial and radial fluctuating velocity of the particles is found to i ncrease with increasing particle relaxation time scale. A method is pr oposed and validated to determine the statistics of the velocity of th e fluid seen by the particles. Measurements are made in the jet far fi eld at x/D = 30. Ejection of solid particles in regions of high outwar d velocity is detected statistically. The fluid-particle correlations are presented and used to analyse the evolution of particle kinetic st resses. The experimental results confirm that the radial particle turb ulent velocity is mainly controlled by the dragging by the fluid turbu lence and decreases with increasing particle relaxation time compared to the fluid turbulence integral time scale. In contrast, production b y the mean particle velocity gradient and transport terms are importan t mechanisms affecting the streamwise particle turbulence velocity. Th ese mechanisms are responsible for the increase in the streamwise part icle turbulence velocity with increasing particle relaxation time. Cop yright (C) 1996 Elsevier Science Ltd.