Turbulent Dynamics and Heat Transfer in Transcritical Channel Flow

Abstract

We present direct numerical simulations (DNS) of turbulent channel flow to study turbulent dynamics and heat transfer effects at a transcritical temperature and supercritical pressure regime. The fully compressible Navier–Stokes equations in conservative form are closed with the Peng–Robinson (PR) equation of state and the Chung’s model for the thermophysical and transport properties. To quantify the turbulent heat transfer effect, the bottom and top walls of the channel are maintained at different isothermal temperatures, Ttop/bot = Tpb±∆T/2, where Tpb is the pseudoboiling temperature of working fluid and ∆T = 20 K. The bulk pressure and velocity are 1.1pc and 36 m/s, respectively, where pc is the critical pressure. The statistical mean profiles shows significant thermophysical variation in the regime having large thermodynamic gradient near the walls compared to the ideal gas case and the average pseudoboiling location is observed at y/h = 0.92. The root mean square (RMS) profiles of fluctuating velocity are attenuated in the pseudogas region, whereas the thermodynamic fluctuations are greater in that region than the pseudoliquid region. One-dimensional energy spectra fall off steeply at high wavenumber showing the adequacy of the DNS resolution. Instantaneous visualizations of near-wall turbulent structures reveal that the dense fluid ejection from the bottom wall reaches to the channel center region resulting in the large fluctuation in the thermodynamic properties across the channel.