Spatial And Temporal Analysis Of Real Fluid Thermodynamics Nonlinearities On Turbulent Mixing In Supercritical Fluids

Abstract

The impact of thermodynamic nonlinearities on flow properties and turbulence was the focus of this study, which investigated the spatial and temporal dynamics of supercritical CO₂ turbulent mixing layers. Beyond their critical point, where parameters such as density, pressure, temperature, isothermal compressibility, and thermal expansion show significant gradients and fluctuations, supercritical fluids deviate sharply from ideal gas behavior. These nonlinearities have a major effect on turbulence and cause complex mixing behavior that has important ramifications for the machines that operate in supercritical environments. The study explored the effects of local variations of important thermodynamic variables on the fluid dynamics in a spatially evolving mixing layer axially along the X axis, and transversely across the mixing layer along the Y axis, using LES. Five locations downstream of a finite splitter plate are the subject of the analysis. This study also analyzed the change of parameters at the intersecting points of vertical stations and centerline with respect to time. Maxwell\u27s relations and the Jacobian inversion method were used to quantify the effects of factors such as isothermal compressibility and the thermal expansion coefficient on observables such as temperature and pressure. The major findings include sudden inflections in the partial derivative of density with respect to pressure, which signify regions of a marked difference in isothermal compressibility. These changes are more pronounced downstream, highlighting the coupling of thermodynamic properties and turbulence. In temperature profiles, it is evident that the rise of fluctuations and sharp gradients enhances the formation of turbulent structures. This highlights the heat expansion effect on the mixing. Also, there are large pressure and enthalpy fluctuations in regions with significant thermodynamic gradients. Pressure fluctuations driven by these nonlinear property increased in amplitude downstream, potentially leading to instabilities in confined environments. In a qualitative sense the study shows that thermodynamic nonlinearities lead to active flow regimes, where turbulence is enhanced. Quantitatively, the outcomes indicate that near the critical point slight perturbations often produce dramatic property changes necessitating advanced modeling methods. These results highlight how thermodynamic nonlinearities are significant to supercritical CO₂ mixing-layer evolution. Index Terms: Bulk thermal expansion coefficient, isothermal compressibility, Large Eddy Simulation, supercritical condition, thermodynamic nonlinearities, and turbulent flow