Study on control of axisymmetric jet by half delta-wing shaped vortex generators (Part 2: Evaluation of statistics on the thermal field)

Abstract

Effects of half delta-wing shaped vortex generators (VGs) on thermal diffusion of an axisymmetric jet are experimentally investigated. The basic experimental setup is same as that of our past study (Miura et al., 2015). Six VGs are equally arrayed around the jet exit. The jet Reynolds number is set to 20,000. The initial temperature of the jet is set to 7.5 K higher than the ambient temperature. Instantaneous velocities and temperature are simultaneously measured by a composite probe which consists of an X-type hot-wire probe and an I-type cold-wire probe. The results show that ambient fluid is rapidly entrained and transported toward the jet center and thermal diffusion is promoted in the case with the VGs. The peak value of the temperature fluctuation in the case with the VGs is smaller than that in the case without the VGs because of the enhanced mixing near the jet exit. The turbulent Prandtl number at the location of half width of the mean velocity is around 0.65 ～ 0.8 in most of the cases but it is around 0.9 between the VGs at x/d = 2. In the downstream region, the effect of the VGs is small.