Particle behavior in a turbulent flow within an axially corrugated geometry

In this numerical study particle behavior inside a sinusoidal pipe geometry is analyzed. The 3D geometry consists of three identical modules, with a periodic boundary condition applied to the flow in the stream wise direction. The incompressible, turbulent gas flow is modeled using a Large Eddy Simulation (LES) approach. Furthermore, the particle dynamics are simulated using a Lagrangian point force approach incorporating the Stokes drag and slip correction factor. Four different sizes of particles, corresponding to a Stokes number less than unity, are considered along with two different inflow conditions: continuous and pulsatile. The pulsatile inflow has an associated flow frequency of 80 Hz. The fluid flow through the sinusoidal pipe is characterized by weak flow separation in the expansion zones of the sinusoidal pipe geometry, where induced shear layers and weak recirculation zones are identified. Particle behavior under the two inflow conditions is quantified using particle dispersion, particle residence time, and average radial position of the particle. No discernible difference in the particle behavior is observed between the two inflow conditions. As the observed recirculation zones are weak, the particles are not retained within the cavities for a long duration of time, thereby reducing their likelihood of agglomerating.

HYDRODYNAMIC FEATURES OF SUSPENSIONS AND EMULSIONS FLOWS.

This scientific article is devoted to the problems associated with the flow of suspensions and emulsions and some simplifications of the real picture of the flow of a polydisperse medium are made. It is also stipulated that differential equations characterizing the motion of suspensions and emulsions should take into account the fundamental discontinuity of the medium and the physicochemical processes of heat and mass transfer occurring in it. Taking into account all these factors, a general equation for multiphase systems is proposed with certain simplifications that do not change. The behavior of particles in two-phase systems, their concentration, collision and coagulation are considered. As a result, it was concluded that there is a multifactorial interaction and mutual influence of both phases in a dispersed flow. A differential equation of motion of a single i-th spherical particle in suspension was proposed, and an equation describing the drag force of a solid spherical particles. Equations of conservation of mass and momentum are presented for one-dimensional laminar motion of two incompressible phases in a gravity field with the same pressure in the phases. Having studied the parameters of the flow of fine particles in a turbulent gas flow, some assumptions were made. It was found that the pulsating motion of particles, performed by them during one period of gas pulsations, can be represented as a change in the pulsating gas velocity in time. The parameter of entrainment of particles by a pulsating medium is an important characteristic in determining the transport coefficients in a turbulent flow. It is concluded that the presence of various kinds of particles in the liquid complicates the problem of solving hydromechanical problems in turbulent and laminar flow, and the assumptions given in the work facilitate the study of this problem.

Small-scale clustering of nano-dust grains in supersonic turbulence

ABSTRACT We investigate the clustering and dynamics of nano-sized particles (nano dust) in high-resolution (10243) simulations of compressible isothermal hydrodynamic turbulence. It is well established that large grains will decouple from a turbulent gas flow, while small grains will tend to trace the motion of the gas. We demonstrate that nano-sized grains may cluster in a turbulent flow (fractal small-scale clustering), which increases the local grain density by at least a factor of a few. In combination with the fact that nano-dust grains may be abundant in general, and the increased interaction rate due to turbulent motions, aggregation involving nano dust may have a rather high probability. Small-scale clustering will also affect extinction properties. As an example we present an extinction model based on silicates, graphite, and metallic iron, assuming strong clustering of grain sizes in the nanometre range, could explain the extreme and rapidly varying ultraviolet extinction in the host of GRB 140506A.

Space-time discontinuous Galerkin method for the numerical simulation of the compressible turbulent gas flow through the porous media

The article is concerned with the numerical simulation of the compressible turbulent gas flow through the porous media using space-time discontinuous Galerkin method.The mathematical model of flow is represented by the system of non-stationary Reynolds-Averaged Navier-Stokes (RANS) equations. The flow through the porous media is characterized by the loss of momentum. This RANS system is equipped with two-equation k-omega turbulence model. The discretization of these two systems is carried out separately by the space-time discontinuous Galerkin method. This method is based on the piecewise polynomial discontinuous approximation of the sought solution in space and in time. We present some numerical experiments to demonstrate the applicability of the method using own-developed code.