Quantification of Dissimilar Destruction between Turbulent Momentum and Heat Fluxes Using Hot- and Cold-Wires

Abstract: We conceived that the dissimilarity between the velocity and temperature fields in a turbulent flow is (at least partially) due to the dissimilar destruction of turbulent fluxes of momentum and heat. In this study, we measured the dissimilar destruction using hot- and cold-wires in a slightly heated (20C above ambient temperature) jet at a Reynolds number of 70,000. In principle, investigation of the destruction of turbulent fluxes requires measurements of the fluctuating pressure. However, because the dissimilar destruction is associated with the instantaneous velocity-gradient ∂v′/∂x and temperature-gradient ∂θ′/∂y with opposite signs, we eliminated the pressure measurements. We used a combined probe consisting of an X-type hot-wire and two cold-wire probes. The results of the simultaneous velocity- and temperature-gradients were in good agreement with the reference results. Spectral coherence and joint PDF between ∂v′/∂x and ∂θ′/∂y show that these quantities do not correlate with each other, indicating a great degree of dissimilarity in the destruction of the turbulent fluxes. Keywords: Round jet, turbulent momentum flux, turbulent heat flux, hot-wire anemometry, cold-wire thermometer