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- Contribution to the Physical Understanding of Supercritical Fluid Flows: A Computational PerspectivePublication . Magalhães, Leandro Barbosa; Silva, André Resende Rodrigues daThe modeling of fluids at supercritical and transcritical regimes is addressed at conditions characteristic of liquid propelled rocket engines, whose increasing performance demands have led to conditions in the combustion chambers to exceed the critical point of both fuels and oxidizers in the pursuit of higher specific impulses. In the present document, nitrogen is used as a surrogate for the commonly encountered oxygenhydrogen mixture so that turbulence mixing can be looked into without influences from combustion and chemically reacting effects. In contrast to the widespread use of compressible formulations in the literature, a distinct hypothesis is formulated and investigated, focusing on fluids’ incompressible but variabledensity behavior at supercritical and transcritical conditions. The incompressible but variabledensity hypothesis arose from the similarity of visualization data, namely measuring mixing efficiency through jet spreading rates. This document evaluates the capabilities and limitations of a computational method (Reynoldsaveraged NavierStokes) developed based on the incompressible variabledensity hypothesis when applied to supercritical and transcritical conditions. Based on the socalled ”thermal breakup mechanism concept” proposed in the literature, the mechanical description of supercritical jets is complemented, demonstrating that the amount of heat a jet receives inside the injector determines if a change from supercritical liquidtogaslike condition takes place, highlighting the importance of including the injector flow in the computations. Axial density and temperature decay rates of supercritical and transcritical jets are predicted for a wide range of conditions and geometries of increasing complexity, ranging from single species injection at supercritical and later transcritical conditions into quiescent environments to coaxial single and multispecies configurations. The results suggest that the incompressible but variable density hypothesis can sufficiently replicate the experimental data, rivaling the predictions of more sophisticated methods relying on large eddy simulation formulations. Moreover, the need to include the injector into the computations for an accurate flow description is demonstrated. Furthermore, the errors resulting from its absence are assessed and evaluated by comparing adiabatic and isothermal boundary conditions. Finally, the proposed solver has also demonstrated its capabilities in the temperature field predictions, making it one of the few solvers currently available to have been validated in terms of density and temperature.