Peculiarities of vortex trace formation in subsonic two-phase flow

The process of unsteady subsonic laminar flow round a simple cube-shaped body with a two-phase flow was investigated. The two-phase flow is a flow of finely dispersed particles of a liquid (water) in a carrier phase (air), which are not mixed with the main flow. Such medium is a model of an aero-suspension. The volume fraction of dispersed water in the aero-suspension did not exceed 1 %. The aim of the work was to investigate the peculiarities of the formation and development of separated currents in the trace during the aero-suspension flow around a cube. The problem was described by the system of the Navier-Stokes equations with the addition of the concentration equation and the equations of state corresponding to the phases and was solved in the framework of the Euler approach, using the VOF method in the multiphaseEulerFoam module, which is a part of the open source package OpenFOAM. The problem was solved in a flat formulation. The discretisation of convective summands over the space was performed using the Van Leer scheme of the second order of accuracy. The reconstruction of the fluxes on the cell faces was performed using the TVD scheme with the gradient constraint, in which the approximation is based on central differences and the Van Leer minmod function is used as a constraint. The resulting system of algebraic equations was solved numerically using the conjugate gradient method with an incomplete diagonal Cholesky preconditioner. The instantaneous fields of pressures, velocities and concentrations of flow phases were obtained. It is revealed and shown that the structure of the two-phase flow of aero-suspension is characterised by the formation of a stagnation region near the frontal surface of the cube and the formation of a vortex trace behind the body. The peculiarities of the formation and development of detached currents in the trace during two-phase medium flow around the cube are revealed and shown. The mechanism of the formation of the vortex trace development is described. It is shown that it is the presence of the second phase in the aero-suspension that leads to the formation of vortex structures and the formation of a viscous vortex track even in laminar flow regimes in the subsonic region.