A fully meshless method for ‘gas – evaporating droplet’ flow modelling

A meshless method for modelling two-phase flows with phase transition is described. The method is based on consideration of three systems: viscous-vortex blobs, thermal-blobs and droplets; and can be applied for numerical simulation of 2D non-isothermal flows of ‘gas-evaporating droplets’ in the framework of the one-way coupled two-fluid approach. The carrier phase is viscous incompressible gas. The dispersed phase is presented by a cloud of identical spherical droplets, and, due to evaporation, the radius and mass of droplets are time dependent. The carrier phase parameters are calculated using the viscous-vortex and thermal-blob method; the dispersed phase parameters are calculated using the Lagrangian approach. Two applications have been considered: (i) a standard benchmark – Lamb vortex; (ii) a cold spray injected into a hot quiescent gas. In the latter problem three cases corresponding to three droplet sizes were investigated. The smallest droplets (of the three cases considered) are more readily entrained by the carrier phase and form ring-like structures; the flow shows better mixing. Larger droplets evaporate less intensively. The medium sized droplets collect into two narrow bands stretched along the jet axis. The largest droplets form a two-phase jet, which remains close to the jet axis. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Aerodynamic focusing of inertial particles in supersonic micronozzles

A particle-laden flow in a supersonic micronozzle is studied using a one-way coupled two-fluid approach. The carrier gas parameters are obtained from the numerical solution of the Navier-Stokes equations, rarefaction effects are taken into account by imposing velocity slip and temperature jump boundary conditions on the nozzle walls. Under conditions considered, the flow around particles is transitional and free-molecular. As a result of numerical solution of the dispersed-phase equations in Lagrangian variables, two types of particle motion in the expanding part of the nozzle are detected: particle spraying and particle accumulation. The particle focusing effect is most pronounced for particles of about 1–2 µm in size. The particle number density fields contain singularities appearing on the envelopes of particle trajectories. However, the model of non-colliding particles remains valid because the mean distance between the particles near the singularities remains much greater than the particle size. The aerodynamic scheme of aerosol particle focusing proposed may be used in various technologies (microthrusters, needle-free drug injection, microfabrication, etc.). (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)