The topology of multiscale turbulent motions in a high-pressure transcritical channel flow is studied using direct numerical simulations. In particular, the system analyzed corresponds to high-pressure (P/Pc=2) microconfined turbulence of N2 at transcritical conditions imposed by a temperature difference between the cold (T/Tc=0.75) and hot (T/Tc=1.5) walls for a friction Reynolds number of Ret=100 (cold wall). The invariants of the velocity-gradient, rate-of-strain, and rate-of-rotation tensors are computed at different length scales. The joint probability density functions of the invariants are calculated and conditioned based on the distance from the walls and additionally compared against an equivalent low-pressure case at isothermal conditions. The results indicate that the presence of higher levels of vorticity close to the hot wall significantly impacts the flow topologies in the viscous sublayer. As a result, topology distributions of the velocity-gradient tensor typical from the outer region are observed in the vicinity of the hot wall. Moreover, the second invariants of the rate-of-strain and rate-of-rotation tensors indicate a large probability of vortex sheet events in the hot (supercritical gaslike) region. Finally, at lengths comparable to the density gradient scale, the presence of vortex sheet structures is diminished with respect to the reference low-pressure case to favor more tubelike flow motions. As inferred from the vorticity transport equation, this behavior is connected to the appearance of a baroclinic-type instability generated from the combination of the external force driving the flow and the large variation of density across the pseudoboiling region.
