Measurement of dissimilar destruction of turbulent momentum and heat fluxes without instantaneous pressure acquisition

Abstract

Pressure–rate-of-strain and pressure–temperature-gradient statistically contribute to the destruction of turbulent momentum and heat fluxes, respectively. However, in instantaneous fields, both forward (loss) and backward (gain) destruction events can occur. Moreover, dissimilar destruction of turbulent fluxes, such as the forward destruction of momentum flux and backward destruction of heat flux, and vice versa, can arise in shear flows. In this study, we experimentally quantify the dissimilarity of turbulent fluxes in a heated round jet. The destruction of the turbulent fluxes is governed by the pressure-rate-of-strain for the momentum flux and the pressure-temperature-gradient of the heat flux. To circumvent the need for instantaneous pressure fluctuation measurements, we employed a combined probe consisting of an X-type hot-wire and two parallel cold-wire sensors. This setup enabled the quantification of the fraction of total events corresponding to dissimilar flux destruction. The combined probe provided accurate velocity and temperature statistics, including their derivatives, except in the outer regions of the jet, where the mean velocity is extremely small. Furthermore, confidence in measuring intermediate-scale fluctuations, which are related to the destruction of turbulent fluxes, is confirmed. Finally, the joint statistics between the velocity and temperature derivatives indicate that the destruction of turbulent fluxes in a free round jet is highly dissimilar. We find that the coherence of the destruction of turbulent fluxes due to intermediate-scale fluctuations is at most 0.4 and decreases with the streamwise distance from the exit and increasing frequency. Furthermore, approximately half of the instantaneous events exhibit dissimilar destruction of the turbulent fluxes.