scholarly journals Time resolved measurements of droplet preferential concentration in homogeneous isotropic turbulence without mean flow

2019 ◽  
Vol 31 (2) ◽  
pp. 025103
Author(s):  
H. Lian ◽  
X. Y. Chang ◽  
Y. Hardalupas
Keyword(s):  
Isotropic Turbulence ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Time Resolved ◽  
Preferential Concentration ◽  
Time Resolved Measurements

Particle Dispersion in Fine Scales of Homogeneous Isotropic Turbulence

2007 ◽  
Author(s):  
M. Sato ◽  
M. Tanahashi ◽  
T. Miyauchi
Keyword(s):  
Isotropic Turbulence ◽  
Major Axis ◽  
Stokes Number ◽  
High Energy ◽  
Energy Dissipation Rate ◽  
Particle Dispersion ◽  
Fine Scale ◽  
Number Density ◽  
Homogeneous Isotropic Turbulence ◽  
Preferential Concentration

Direct numerical simulations of homogeneous isotropic turbulence laden with particles have been conducted to clarify the relationship between particle dispersion and coherent fine scale eddies in turbulence. Dispersion of 106 particles are analyzed for several particle Stokes numbers. The spatial distributions of particles depend on their Stokes number, and the Stokes number that causes preferential concentration of particles is closely related to the time scale of coherent fine scale eddies in turbulence. On the plane perpendicular to the rotating axes of fine scale eddies, number density of particle with particular Stokes number is low at the center of the fine scale eddy, and high in the regions with high energy dissipation rate around the eddy. The maximum number density can be observed at about 1.5 to 2.0 times the eddy radius on the major axis of the fine scale eddy.

Simulation of Interactions Between Microbubbles and Turbulent Flows

1994 ◽  
Vol 47 (6S) ◽  
pp. S70-S74 ◽  
Author(s):  
M. R. Maxey ◽  
E. J. Chang ◽  
L. -P. Wang
Keyword(s):  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Small Scale ◽  
Air Bubbles ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Drag Forces ◽  
Spherical Inclusions ◽  
Average Rise ◽  
Surrounding Fluid

Microbubbles formed by small air bubbles in water are characterized as spherical inclusions that are essentially rigid due to the effects of surfactants, and respond to the action of drag forces and added-mass effects from the motion relative to the surrounding fluid. Direct numerical simulations of homogeneous, isotropic turbulence are used to study the effects of the small-scale, dissipation range turbulence on microbubble transport and in particular the average rise velocity of microbubbles. It is found that microbubbles rise significantly more slowly than in still fluid even in the absence of a mean flow, due to a strong interaction with the small-scale vorticity. The way in which microbubbles might modify the underlying turbulence by the variations in their local distribution is discussed for dilute, dispersed systems and some estimates for the enhanced viscous dissipation given.

Lift Force Effects on the Behavior of Bubbles in Homogeneous Isotropic Turbulence

2005 ◽  
Author(s):  
Mustapha Abbad ◽  
Benoiˆt Oesterle´
Keyword(s):  
Relative Velocity ◽  
Lift Force ◽  
Isotropic Turbulence ◽  
Stokes Number ◽  
Rise Velocity ◽  
Homogeneous Isotropic Turbulence ◽  
Preferential Concentration ◽  
Coupling Approximation ◽  
Lagrangian Tracking ◽  
Small Bubbles

The influence of lift forces on the dispersion of small bubbles is numerically studied in a homogeneous isotropic turbulence generated by random Fourier modes, under one-way coupling approximation. The effects of bubble Stokes number and mean relative velocity are investigated by computing the statistics from Lagrangian tracking of a large number of bubbles in many flow field realizations, and comparison is provided between the results obtained with and without taking the lift force into account. The effects of preferential concentration, which are known to reduce the terminal rise velocity of bubbles, are also investigated. The lift force is found to drastically modify the correlations and integral time scales of the fluid seen by the bubbles in their fluctuating motion, and to significantly enhance the accumulation of bubbles in high vorticity regions.

Evolution of enstrophy in shock/homogeneous turbulence interaction

2012 ◽  
Vol 707 ◽  
pp. 74-110 ◽  
Author(s):  
Krishnendu Sinha
Keyword(s):  
Shock Wave ◽  
Numerical Simulations ◽  
High Speed ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Interaction Analysis ◽  
Direct Numerical Simulations ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Linear Interaction

AbstractInteraction of turbulent fluctuations with a shock wave plays an important role in many high-speed flow applications. This paper studies the amplification of enstrophy, defined as mean-square fluctuating vorticity, in homogeneous isotropic turbulence passing through a normal shock. Linearized Navier–Stokes equations written in a frame of reference attached to the unsteady shock wave are used to derive transport equations for the vorticity components. These are combined to obtain an equation that describes the evolution of enstrophy across a time-averaged shock wave. A budget of the enstrophy equation computed using results from linear interaction analysis and data from direct numerical simulations identifies the dominant physical mechanisms in the flow. Production due to mean flow compression and baroclinic torques are found to be the major contributors to the enstrophy amplification. Closure approximations are proposed for the unclosed correlations in the production and baroclinic source terms. The resulting model equation is integrated to obtain the enstrophy jump across a shock for a range of upstream Mach numbers. The model predictions are compared with linear theory results for varying levels of vortical and entropic fluctuations in the upstream flow. The enstrophy model is then cast in the form of$k$–$\epsilon $equations and used to compute the interaction of homogeneous isotropic turbulence with normal shocks. The results are compared with available data from direct numerical simulations. The equations are further used to propose a model for the amplification of turbulent viscosity across a shock, which is then applied to a canonical shock–boundary layer interaction. It is shown that the current model is a significant improvement over existing models, both for homogeneous isotropic turbulence and in the case of complex high-speed flows with shock waves.

scholarly journals Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows

2015 ◽  
Vol 766 ◽  
pp. 104-128 ◽  
Author(s):  
Matthaus U. Babler ◽  
Luca Biferale ◽  
Luca Brandt ◽  
Ulrike Feudel ◽  
Ksenia Guseva ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Turbulent Channel Flow ◽  
Stochastic Flow ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Flow Properties ◽  
Developed Turbulence ◽  
Flow Configurations

AbstractBreakup of small aggregates in fully developed turbulence is studied by means of direct numerical simulations in a series of typical bounded and unbounded flow configurations, such as a turbulent channel flow, a developing boundary layer and homogeneous isotropic turbulence. The simplest criterion for breakup is adopted, whereby aggregate breakup occurs when the local hydrodynamic stress ${\it\sigma}\sim {\it\varepsilon}^{1/2}$, with ${\it\varepsilon}$ being the energy dissipation at the position of the aggregate, overcomes a given threshold ${\it\sigma}_{cr}$, which is characteristic for a given type of aggregate. Results show that the breakup rate decreases with increasing threshold. For small thresholds, it develops a scaling behaviour among the different flows. For high thresholds, the breakup rates show strong differences between the different flow configurations, highlighting the importance of non-universal mean-flow properties. To further assess the effects of flow inhomogeneity and turbulent fluctuations, the results are compared with those obtained in a smooth stochastic flow. Furthermore, we discuss the limitations and applicability of a set of independent proxies.

Experiments and Simulations on Turbulence Modification by Dispersed Particles

1994 ◽  
Vol 47 (6S) ◽  
pp. S44-S48 ◽  
Author(s):  
John K. Eaton
Keyword(s):  
Numerical Simulations ◽  
Gas Phase ◽  
Fine Particles ◽  
Isotropic Turbulence ◽  
Homogeneous Isotropic Turbulence ◽  
Preferential Concentration ◽  
Turbulence Modification ◽  
Dispersed Particles ◽  
Simple Flows ◽  
Highly Strained

Experiments and direct numerical simulations on simple flows have been performed to examine the attenuation of gas-phase turbulence by fine particles. The experiments were performed in a developing boundary layer and in a fully developed channel flow. Both showed significant turbulence attenuation for mass loading ratios greater than 10%. Numerical simulations on homogeneous/isotropic turbulence show similar levels of turbulence attenuation. Both experiments and simulations have demonstrated the importance of preferential concentration in which particles are collected in highly strained regions of the flow. Two-equation models for turbulence attenuation have been found to be inadequate when preferential concentration occurs.

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