Experimental investigations and theoretical calculations devoted to studying different aspects of the formation of clusters in two-phase flows are reviewed. The physical mechanisms of the formation of the regions of increased concentrations of particles in turbulent flows and under flowing bodies by two-phase streams, as well as in free concentrated vortices, are considered.

Clusterization of particles in turbulent and vortex two-phase flows

Particle removal from a surface by a bounded vortex flow

The motion of a dispersed inertial admixture in a steady-state axisymmetric 3D viscous incompressible flow formed by a semi-infinite vortex filament interacting with an orthogonally located substrate surface is considered. The carrier-phase parameters are found from the numerical solution of the Navier-Stokes equations under the assumption of flow self-similarity of a known type [1]. Different phase force interaction schemes corresponding to different ratios of the phase densities are considered. For calculating the dispersed-phase continuum parameters, a full Lagrangian approach is used, which makes it possible to calculate the dispersed-phase concentration in particle accumulation zones and regions of intersecting particle trajectories. On the basis of parametric calculations, it is found that in the case of heavy particles (whose density is greater than that of the carrier phase) a “cup-shaped” particle accumulation surface visualizing a high-vorticity region is formed. The dependence of this surface shape on the governing parameters is investigated. It is shown that for different phase density ratios the dispersed-phase concentration fields are qualitatively different.

Structure of inertial-admixture accumulation zones in a tornado-like flow

The results of an investigation of the unsteady flow structure in a turbulent swirling jet obtained using the PIV technology are presented. The greater part of the measurements is carried out at the swirl intensity W
 0 ≈ 1.7. A part of the data is obtained under other conditions of the swirl jet outflow. To establish the relation between disturbances of different types the phase averaging technique is employed with the pressure fluctuation in the acoustic field of the jet taken as a reference signal. The flow structure is numerically calculated. The results of the investigation show that a quasisteady inhomogeneity observable in the jet flow executes rotational motion relative to the mean flowfield in the jet cross-section, or “precession”. It causes disturbances in the flow ejected by the jet, which transform into acoustic disturbances far away from the jet. The frequencies of the dynamic disturbances near the jet and the acoustic disturbances far away from it coincide with the precession frequency.

Investigation of unsteady processes, flow properties, and tonal acoustic radiation of a swirling jet

In the previous experimental studies it was concluded that the turbulent jet noise is produced by large-scale motions in the mixing layer induced by turbulence intermittence. The burden of this numerical simulation is the validation of these conclusions. As a result of numerical calculations, the “instantaneous” flow patterns and the parameter distributions in the initial regions of turbulent jets are obtained. On the basis of this information the flow dynamics are investigated. In the jet flow there are observable slowly transforming low static pressure regions and zones of elevated static pressure. These regions are displaced at the convection velocity. The inflow induced by the low pressure in the mixing layer has streamlines entering into the low pressure zones and flowing around the elevated pressure zones. The motion of the zones of the static pressure varying along the flow produces velocity disturbances in the induced external flow. The succession of the transformations of the intermittence-induced static pressure disturbances into sound waves is determined. This transformation occurs in the regions occupied by the ejected air.

Investigation of noise generation by turbulent jets on the basis of numerical simulation of unsteady flow in mixing layers

Free turbulent jets produce disturbances in the ambient medium which at a certain distance from the jet are perceived as sound waves. These disturbances are due to unsteady fluctuating motion of the medium in the jet flow (intermittance). The origin of the acoustic disturbances can be attributed to turbulence intermittance. Due to lowered pressure in the movable dynamic inhomogeneities of the turbulent fluid, they induce air ejection by the jet, which turns out to be fluctuating in nature, since the turbulent fluid flow is unsteady. The proposed mechanism of the generation of acoustic disturbances accompanying turbulent jet propagation is verified in numerical and experimental studies; in particular, the formation of acoustic fluctuations in the half-space over a surface which contains an embedded fluctuating finite-size sink is considered on the basis of the numerical solution of the unsteady Reynolds equations. From the results of the numerical experiment performed using large eddy simulation the fluctuating characteristics of the flow in a swirling jet and the direction of the disturbance energy flux in the ambient medium are determined. An experimental investigation of the disturbances produced by a strongly swirling jet is also carried out.

Investigation of the generation of sound waves produced by turbulent jets

The structure and the properties of the air flow developing when an intake system (in particular, a turbojet engine) operates near a surface are studied. On the basis of numerical calculations, the conditions of onset, the intensity, and the structure of the vortex flow ascending from the surface toward the intake are determined. From an analysis of the particle transport toward the intake by the vortex flow, the main factors responsible for the rise of large particles and objects are determined and the conditions of minimization of the probability of large particles entering the intake are found.

Induced flow and ascent of heavy particles when an air intake operates near a surface

The results of a special investigation of the diffuser flowfield are presented for two models of curvilinear diffuser channels with annular and rectangular cross-sections. The flow is visualized and the total pressure fields are measured by means of low-inertia transducers. At the same time, the flows are numerically calculated using commercial programs, together with codes developed by the authors. In these calculations the stationary and time-dependent Reynolds equations closed by different turbulence models, as well as the time-dependent Navier-Stokes equations, were integrated. A considerable difference between the measured data and the results of the numerical calculations in the stationary formulation is found to exist. At the same time, it has been possible to describe the occurrence of spatial inhomogeneities, the flow pattern, and the level of the experimentally observed aerodynamic losses on the basis of the solution of time-dependent problems.

Experimental and Numerical Investigation of Separated Flows in Subsonic Diffusers

Examples of numerical simulation of complex turbulent flows and accompanying problems

Numerical procedure of DBD modeling based on RANS equations has been developed and tested in present study both for the standard DBD and DBD working in constricted mode. Qualitative and approximate quantitative correspondence between known experimental data and numerical results has been achieved. Typical volume force and heat magnitudes has been evaluated, these values could be used as estimation in steady approximation calculations. Both DBD actuators models has shown up that required volume force magnitude has to be increased by 2-3 orders influence on flow separation in S-type engine ducts at relatively high inlet velocity Different method of volume force calculation using actuator electrical parameters (DPM) has been carried out. Continuous volume force components fields have been calculated as a function of DBD actuator potential difference and charge density amplitude.

D. E. Pudovikov

Papers

Investigation of the generation of sound waves produced by turbulent jets

Induced flow and ascent of heavy particles when an air intake operates near a surface

Experimental and Numerical Investigation of Separated Flows in Subsonic Diffusers

Examples of numerical simulation of complex turbulent flows and accompanying problems

Numerical simulation of interaction process between dielectric barrier discharge and duct flow