Abstract

Jets are used in several engineering applications including dilution and mixing. The counter flowing free jet was investigated to find the penetration length and geometry of the expanded jet. The turbulence characteristics of the counter flowing free jets have been determined. Several jet nozzles with different diameters were used to form the jet located at the center of a closed conduit that had a square cross section. The results show that the penetration length varies linearly with the ratio of the jet velocity to the main flow velocity that is denoted by R. Axial and radial velocity components were measured simultaneously using a 2-D laser velocity probe. The raw data was processed and several characteristics of the counter flowing free jets such as the decay rate of the jet and the turbulence behavior of the jet along the jet axis are reported. The turbulent kinetic energy of the counter flowing free jets was studied. Several profiles were chosen and the turbulent kinetic energy was balanced along the radial direction of the jet. The terms including pressure component were used as the closure, since the pressure was not measured. Another major part of the study was to find the wake mixing characteristics of the counter flowing free jets. Several tests with different R values were performed and for each test, the concentration of the tracer injected by the jet to the main flow was measured at several points at different cross sections in the near wake region of the jet. The results show that the mixing between the tracer and the main flow improves with larger jet diameter and bigger velocity ratios. A small part of the study was devoted to numerical test using the software code, Phoenics. Three sets of tests using different turbulence models were performed and the results were compared with the measurement. In comparison, for the case of turbulent jets in counter flow, the k-f model gave a better result than k-} and mixing length models. The results can be applied directly to the control of stream pollution, as the counter flowing free jet is a very effective device to dilute the effluents injected in a stream