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This paper evaluates the suitability of a newly developed hybrid “Langmuir–Maxwell” and “Langmuir–Smoluchowski” slip/jump boundary conditions in the Navier–Stokes–Fourier equations for nano-/micro-backward-facing step geometry flow which experiences separation and reattachment. Additionally, this paper investigates the effect of different parameters such as step pressure ratio, inflow temperature, and wall temperature on the separation zone in the nano-/micro-step geometry. We chose nitrogen as the working gas and use two direct simulation Monte Carlo (DSMC) solvers to assess the accuracy of the computational fluid dynamics (CFD) solutions. DSMC results showed that the increase of the inlet temperatures extends the length of the separation zone and raises the mass flow rate. The change of pressure ratio does not affect the separation length while the increase of the step wall temperature decreases the length of this zone for both CFD and DSMC results. Compared to the DSMC results, the hybrid slip/jump boundary conditions predict better surface pressure, surface gas temperature, and slip velocity in the separation zone than the standard Maxwell/Smoluchowski boundary conditions. [ABSTRACT FROM AUTHOR]

In this study, transient 2D/axisymmetric simulations of cavitating flows are performed using a modified 'Volume-of-Fluid' (VOF) technique. Simulation of the cavitation is based on a homogenous equilibrium flow model. To predict the shape of the cavity, the Navier-Stokes equations in addition to an advection equation for the liquid volume fraction are solved. Mass transfer between the phases is treated as a sink term in the VOF equation. The numerical method is used for different geometries in a wide range of cavitation numbers. Computed shapes of cavities were found to be in good agreement with those of the reported experiments. The simulation results also compared well with those obtained from analytical relations. [ABSTRACT FROM AUTHOR]