Oyuna Rybdylova

Modelling of a two-phase vortex-ring flow using an analytical solution for the carrier phase

Abstract A transient axially symmetric two-phase vortex-ring flow is investigated using the one-way coupled, two-fluid approach. The carrier phase parameters are calculated using the approximate analytical solution suggested by Kaplanski and Rudi (Phys. Fluids vol. 17 (2005) 087101–087107). Due to the vortical nature of the flow, the mixing of inertial admixture can be accompanied by crossing particle trajectories. The admixture parameters are calculated using the Fully Lagrangian Approach (FLA). According to FLA, all of the dispersed phase parameters, including the particle/droplet concentration, are calculated from the solution to the system of ordinary differential equations along chosen particle trajectories; FLA provides high-accuracy particle number calculations even in the case of crossing particle trajectories (multi-valued fields of the dispersed media). Two flow regimes corresponding to two different initial conditions are investigated: (i) injection of a two-phase jet; and (ii) propagation of a vortex ring through a cloud of particles. It was shown that the dispersed media may form folds and caustics in these flows. In both cases, the ranges of governing parameters leading to the formation of mushroom-like clouds of particles are identified. The caps of the mushrooms contain caustics or edges of folds of the dispersed media, which correspond to particle accumulation zones.

Meshless methods for ‘gas ‐ evaporating droplet’ flow modelling

The main ideas of simulation of two-phase flows, based on a combination of the conventional Lagrangian method or Osiptsov method for the dispersed phase and the mesh-free vortex and thermal blob methods for the carrier phase, are summarised. A meshless method for modelling of 2D transient, non-isothermal, gas-droplet flows with phase transitions, based on a combination of the viscous-vortex and thermal-blob methods for the carrier phase with the Lagrangian approach for the dispersed phase, is described. The one-way coupled, two-fluid approach is used in the analysis. The method makes it possible to avoid the ‘remeshing’ procedure (recalculation of flow parameters from Eulerian to Lagrangian grids) and reduces the problem to the solution of three systems of ordinary differential equations, describing the motion of viscous-vortex blobs, thermal blobs, and evaporating droplets. The gas velocity field is restored using the Biot–Savart integral. The numerical algorithm is verified against the analytical solution for a non-isothermal Lamb vortex. The method is applied to modelling of an impulse two-phase cold jet injected into a quiescent hot gas, taking into account droplet evaporation. Various flow patterns are obtained in the calculations, depending on the initial droplet size: (i) low-inertia droplets, evaporating at a higher rate, form ring-like structures and are accumulated only behind the vortex pair; (ii) large droplets move closer to the jet axis, with their sizes remaining almost unchanged; and (iii) intermediate-size droplets are accumulated in a curved band whose ends trail in the periphery behind the head of the cloud, with larger droplets being collected at the front of the two-phase region.

A model for mono- and multi-component droplet heating and evaporation and its implementation into ANSYS Fluent

A model for heating and evaporation of mono- and multi-component droplets, based on analytical solutions to the heat transfer and species diffusion equations in the liquid phase, is summarised. The implementation of the model into ANSYS Fluent via User-Defined Functions (UDF) is described. The model is applied to the analysis of pure acetone, ethanol, and mixtures of acetone/ethanol droplet heating/cooling and evaporation. The predictions of the customised version of ANSYS Fluent with the newly implemented UDF model are verified against the results predicted by the previously developed in house, one-dimensional code. DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4759

Numerical study of nanoparticle formation in a free turbulent jet

Di-ethyl-hexyl-sebacate (DEHS) aerosol nanoparticle formation in a free turbulent jet as a result of nucleation, condensation and coagulation is studied using fluid flow simulation and the method of moments under the assumption of lognormal particle size distribution. The case of high nucleation rates and the coagulation-controlled growth of particles is considered. The formed aerosol performance is jet is numerically investigated for the various nozzle diameters and two approximations of the saturation pressure dependence on the temperature. It is demonstrated that a higher polydispersity of the aerosol is obtained for smaller nozzle diameters.