Turbulence statistics of homogeneous isotropic supercritical fluid flow

At supercritical pressures, intermolecular forces and molecular packing effects strongly influence fluid behavior, leading to thermodynamic and transport properties that differ significantly from those at subcritical pressures. At these conditions, the resulting high-pressure thermodynamic state space can be divided into liquidlike and gaslike regimes, separated by the pseudoboiling region, where thermophysical properties change rapidly. In this regard, the effects of real-fluid properties and pseudoboiling phenomena on turbulence at <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mtext>Re</a:mtext> <a:mi>λ</a:mi> </a:msub> <a:mo>=</a:mo> <a:mn>30</a:mn> </a:mrow> </a:math> and <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:msub> <b:mtext>Ma</b:mtext> <b:mi>t</b:mi> </b:msub> <b:mo>=</b:mo> <b:mn>0.1</b:mn> </b:mrow> </b:math> are investigated through direct numerical simulations of isotropic turbulence in five thermodynamic states of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msub> <c:mi>CO</c:mi> <c:mn>2</c:mn> </c:msub> </c:math> : one liquidlike, one gaslike, and three pseudoboiling conditions. The thermophysical operating conditions result in Prandtl numbers greater than one, leading to the generation of sub-Kolmogorov thermal scales. Turbulence statistics are, thus, assessed through spectra, probability density functions, and higher-order moments. Temperature-related quantities are particularly sensitive to supercritical fluid effects, showing increased intermittency in the temperature variance dissipation rate and reduced production of mean-square temperature gradients, particularly in strong pseudoboiling conditions. Finally, local flow topology is analyzed using joint probability density functions of the velocity gradient invariants, conditioned on regions with intense pseudoboiling activity. These regions are found to suppress strain-dominated structures while enhancing vortical motions.