Near-wall turbulence in channel flow boundary layer with large thermophysical property fluctuations at supercritical pressure*

Direct numerical simulations of turbulent channel flow boundary layers are conducted using CO2 as a working fluid at supercritical pressure (SCP). The channel upper and lower walls are treated as isothermally heated and cooled, respectively, ensuring the pseudo-boiling process occurs in the channel flow. The objective is to elucidate how the property variations affect the first- and second-order turbulence statistics, near-wall scaling laws, and turbulence anisotropy. The results demonstrate that large property fluctuations occur near the heated wall due to the proximity of the pseudo-boiling point. This real-fluid effect leads to the failure of conventional temperature scaling law and promotes turbulence anisotropy. A new scaling law based on enthalpy calibration utilizing energy conservation is proposed to exhibit substantial improvement. The budget analysis shows that drastic changes in thermophysical properties lead to the redistribution of turbulent kinetic energy among different components, resulting in turbulence anisotropy. Further insights are gained through turbulence statistical decomposition, quadrant analysis, and instantaneous flow snapshots. These results could enhance the understanding of the impact of drastic property changes on near-wall turbulence in SCP fluids and provide guidance for turbulence modeling of SCP fluids.