Author(s): Adrian C. H. Laii, Peng Liu, Adria W. K. Law, E. Eric Adams
Linked Author(s): Adrian Lai
Keywords: Jets, plumes, ambient turbulence, second order statistics, integral models
Abstract: Jets and plumes can be seen in many natural and man-made environments and processes. The ambient which the jets discharge into is often not quiescent but weakly turbulent, which can somewhat change the mixing characteristics of the jet or plume. As a first step, to better understand the mixing of a jet in ambient turbulence, experiments are carried out in a 2. 4 m (long) x 1. 2 m (wide) x 2 m (tall) water tank. An array of submerged bilge pumps is placed at one end of the tank; each of them is switched on and off at random time and interval to generate an array of randomly pulsating jets. The pulsating jets are mixed in the tank and generated an approximately isotropic and homogeneous turbulence. A pure jet from a nozzle with diameter D = 1. 0 cm discharged at an initial velocity uo = 0. 63 m/s into the ambient turbulence (root-mean-square velocity ? 2 cm/s; integral length scale ? 9 cm). The instantaneous velocity field of the jet is then measured with Particle Image Velocimetry (PIV) at a distance of 10D � 30D from the source at a frequency of 50Hz. We then extract the velocity and spreading the rate of the jet in ambient turbulence. We also extract the second order statistics, such as the jet axial and shear stresses from the PIV measurements. It is shown that the jet momentum is conserved only if the jet second order statistics are taken into account, which previously have often been overlooked. The conservation of momentum is an important governing equation for predictive jet integral models, and an outline of such model will be given in this paper
Year: 2017