Turbulent Scalar Transport Mechanism and Velocity-Temperature Natural Dissimilarity in a Turbulent Plane Couette Flow

Abstract

The direct numerical simulation, DNS, of a fully developed turbulent plane Couette flow with heat transfer has been performed. The main goals of the present work is to analyse natural dissimilarity, and axial momentum and thermal energy turbulent transport mechanism in this kind of turbulence. It has been chosen a low Reynolds number equal to 1,300 as a function of half the walls distance and half the velocity of the moving wall. This Reynolds gives a Reynolds number as a function of half walls distance and friction velocity of about 84. The energy equation was solved for a molecular Prandtl number equal 1, and with isothermal boundary conditions at both walls. For instance, the streamwise velocity and temperature fields were solved with the same kind of boundary conditions, in order to have the same direction of momentum and thermal turbulent fluxes. Buoyancy effects were neglected, thus the temperature was considered as a passive scalar.
The main results of this work show that axial velocity and temperature fluctuations have the same kind of natural dissimilarity present in turbulent channel flow. While natural de-correlation between axial velocity and temperature fluctuations starts in the very near-wall region due to the most energetic events there, the contribution of these events to the total natural dissimilarity is less than fifty percent in the
whole flow.
Analysis of longitudinal velocity and temperature fluctuations in the frequency domain, using spectral density functions, shows that the main cause of natural dissimilarity is the shift toward higher frequencies of temperature fluctuations in comparison to those belong to axial velocity, in the viscous,
buffer, and beginning of the logarithmic region. Based on the spectra of pressure fluctuations and wall normal fluctuations, it is clear that wall normal velocity plays an important role in the natural dissimilarity of streamwise velocity and temperature fluctuation fields.