Enhancement of turbulent diffusion in an axisymmetric jet by vortex generators

Abstract

Effects of vortex generators (VGs) on fluid entrainment and thermal diffusion on an axisymmetric jet are experimentally investigated. A weakly-heated air is introduced from the circular skimmer to the test section. The skimmer diameter is 30mm and the Reynolds number based on the diameter and the initial jet velocity is set to 20,000. The VGs have a shape of a half delta-wing and they are installed circumferentially on the edge of the skimmer. Eleven VGs configurations are tested by changing the number of the VGs and their intervals. Instantaneous velocity and temperature are simultaneously measured using a hot wire anemometer and a cold wire thermometer, respectively. The results show that the VGs increase fluid entrainment in the upstream region but become ineffective in the downstream region. The VGs also promote thermal diffusion and the effectiveness increases with the number of the VGs. The present study suggests that it is possible to control jet diffusion by arranging the numbers and locations of the VGs.