scholarly journals Droplets in isotropic turbulence: deformation and breakup statistics

2018 ◽  
Vol 852 ◽  
pp. 313-328 ◽  
Author(s):  
Samriddhi Sankar Ray ◽  
Dario Vincenzi
Keyword(s):  
Newtonian Fluid ◽  
Capillary Number ◽  
Drop Size ◽  
Isotropic Turbulence ◽  
Vector Model ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Lifetime ◽  
Initial Drop ◽  
The Mean ◽  
Neutrally Buoyant

The statistics of the deformation and breakup of neutrally buoyant sub-Kolmogorov ellipsoidal drops is investigated via Lagrangian simulations of homogeneous isotropic turbulence. The mean lifetime of a drop is also studied as a function of the initial drop size and the capillary number. A vector model of a drop previously introduced by Olbricht et al. (J. Non-Newtonian Fluid Mech., vol. 10, 1982, pp. 291–318) is used to predict the behaviour of the above quantities analytically.

Influence of Downstream Distance on the Drop Size Characteristics of an Evaporative Liquid Spray in a Convective Gaseous Medium

1992 ◽  
Vol 114 (1) ◽  
pp. 70-74 ◽  
Author(s):  
S. P. Sengupta ◽  
A. K. Mitra ◽  
S. K. Dash ◽  
S. K. Som
Keyword(s):  
Drop Size ◽  
Free Stream ◽  
Axial Distance ◽  
Numerical Studies ◽  
Spray Axis ◽  
Mean Diameter ◽  
Liquid Spray ◽  
Initial Drop ◽  
The Mean ◽  
Light Scattering Technique

Numerical studies have been made to evaluate the interdependence of drop size characteristics and evaporation histories of an atomized liquid spray in a convective medium of uniform free stream at high temperature. With the help of a discrete droplet evaporation model, both the actual drop size distribution and the apparent one, that could have been obtained in practice by light-scattering technique, have been determined numerically at different downstream locations perpendicular to the spray axis. Variations of actual and apparent mass mean diameter and the evaporation rate with the axial distance of the spray have been established. Finally, the influences of pertinent input parameters, namely, the initial Reynolds number of the spray, the ratio of free stream to initial drop temperature and the ratio of free stream to initial drop velocity on the mean diameter and evaporation histories have been recognized.

DNS study of decaying homogeneous isotropic turbulence with polymer additives

2010 ◽  
Vol 665 ◽  
pp. 334-356 ◽  
Author(s):  
W.-H. CAI ◽  
F.-C. LI ◽  
H.-N. ZHANG
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Newtonian Fluid ◽  
Isotropic Turbulence ◽  
Transport Equations ◽  
Vortex Structures ◽  
Small Scale ◽  
Polymer Additives ◽  
Homogeneous Isotropic Turbulence ◽  
Turbulent Drag

In order to investigate the turbulent drag reduction phenomenon and understand its mechanism, direct numerical simulation (DNS) was carried out on decaying homogeneous isotropic turbulence (DHIT) with and without polymer additives. We explored the polymer effect on DHIT from the energetic viewpoint, i.e. the decay of the total turbulent kinetic energy and energy distribution at each scale in Fourier space and from the phenomenological viewpoint, i.e. the alterations of vortex structures, the enstrophy and the strain. It was obtained that in DHIT with polymer additives the decay of the turbulent kinetic energy is faster than that in the Newtonian fluid case and a modification of the turbulent kinetic energy transfer process for the Newtonian fluid flow is observed due to the release of the polymer elastic energy into flow structures at certain small scales. Besides, we deduced the transport equations of the enstrophy and the strain, respectively, for DHIT with polymer additives. Based on the analyses of these transport equations, it was found that polymer additives depress both the enstrophy and the strain in DHIT as compared to the Newtonian fluid case, indicating the inhibition effect on small-scale vortex structures and turbulence intensity by polymers.

Enstrophy transport in swirl combustion

2019 ◽  
Vol 876 ◽  
pp. 715-732 ◽  
Author(s):  
Askar Kazbekov ◽  
Keishi Kumashiro ◽  
Adam M. Steinberg
Keyword(s):  
Isotropic Turbulence ◽  
Reynolds Numbers ◽  
The Other ◽  
Homogeneous Isotropic Turbulence ◽  
Relative Significance ◽  
Swirl Combustion ◽  
Image Velocimetry ◽  
Baroclinic Torque ◽  
Planar Laser ◽  
The Mean

The contributions of vortex stretching, dilatation, baroclinic torque and viscous diffusion to Reynolds-averaged enstrophy transport in turbulent swirl flames were experimentally measured using tomographic particle image velocimetry and $\text{CH}_{2}\text{O}$ planar laser induced fluorescence at jet Reynolds numbers of 26 000–51 000. The mean baroclinic torque was determined by subtracting the other terms in the enstrophy transport equation from the mean Lagrangian derivative. Enstrophy production from baroclinic torque was found to be significant relative to the other transport terms across all conditions studies. This result contrasts with direct numerical simulations of flames in homogeneous isotropic turbulence, which show a decreasing relative significance of baroclinic torque with increasing turbulence intensity (e.g. Bobbitt, Lapointe & Blanquart, Phys. Fluids, vol. 28 (1), 2016, 015101). Hence, the significance of baroclinic enstrophy production in flames is not determined entirely by the local turbulence and flame properties, but also depends on the configuration-specific pressure field.

On the motion of gas bubbles in homogeneous isotropic turbulence

1997 ◽  
Vol 336 ◽  
pp. 221-244 ◽  
Author(s):  
P. D. M. SPELT ◽  
A. BIESHEUVEL
Keyword(s):  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Gas Bubbles ◽  
Numerical Data ◽  
Equation Of Motion ◽  
Equivalent Diameter ◽  
Approximate Analysis ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Velocity ◽  
The Mean

This paper is concerned with the motion of small gas bubbles, equivalent diameter about 1.0 mm, in isotropic turbulent flows. Data on the mean velocity of rise and the dispersion of the bubbles have been obtained numerically by simulating the turbulence as a sum of Fourier modes with random phases and amplitudes determined by the Kraichnan and the von Kármán–Pao energy-spectrum functions, and by calculating the bubble trajectories from a reasonably well-established equation of motion. The data cover the range β[les ]1, where β is the ratio between the turbulence intensity and the velocity of rise of the bubbles in still fluid. An approximate analysis based on the assumption that β is small yields results that compare favourably with the numerical data, and clarifies the important role played by the lift forces exerted by the fluid.

A shear-free turbulent boundary layer

1967 ◽  
Vol 28 (4) ◽  
pp. 803-821 ◽  
Author(s):  
T. Uzkan ◽  
W. C. Reynolds
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Isotropic Turbulence ◽  
Wall Turbulence ◽  
Statistical Features ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Velocity ◽  
Velocity Gradients ◽  
The Mean

A simple wall-turbulence interaction has been studied experimentally. In the idealized model an infinite flat plate is suddenly inserted into a pre-existing field of homogeneous isotropic turbulence, and subsequent changes in the turbulence field examined. The experiment involved passing grid-produced turbulence over a wall moving at the mean speed. Mean velocity gradients vanish in both the model and experiment, and hence production of new turbulence is absent. This allowed the inhibiting effects of the wall to be studied separately. The growth of the ‘inhomogeneity layer’ into the impressed turbulence field and other statistical features of the turbulence were measured.

A statistical theory of turbulent relative dispersion

2007 ◽  
Vol 571 ◽  
pp. 391-417 ◽  
Author(s):  
P. FRANZESE ◽  
M. CASSIANI
Keyword(s):  
Laboratory Experiments ◽  
Isotropic Turbulence ◽  
Diffusion Theory ◽  
Relative Dispersion ◽  
Inertial Subrange ◽  
Mean Square ◽  
Homogeneous Isotropic Turbulence ◽  
Relative Kinetic ◽  
The Mean ◽  
Closure Assumption

The laws governing the spread of a cluster of particles in homogeneous isotropic turbulence are derived using a theoretical approach based on inertial subrange scaling and statistical diffusion theory. The equations for the mean square dispersion of a puff admit an analytical solution in the inertial subrange and at large scales. The solution is consistent with Taylor's theory of absolute dispersion. An analytical derivation of the Richardson–Obukhov constant of relative dispersion is presented. A time scale for relative dispersion is identified, as well as relations between Lagrangian and Eulerian structure functions. The results are extended to turbulence at finite Reynolds number. A closure assumption for the relative kinetic energy, based on Taylor's theory, is presented. Comparisons with direct numerical simulations and laboratory experiments are reported.

Temperature Dependences in the O + OH → O2 + H Reaction. Quasiclassical Trajectory Calculation

1993 ◽  
Vol 58 (2) ◽  
pp. 234-243 ◽  
Author(s):  
Viliam Klimo ◽  
Martina Bittererová ◽  
Stanislav Biskupič ◽  
Ján Urban ◽  
Miroslav Micov
Keyword(s):  
Temperature Dependence ◽  
Energy Surface ◽  
Analytical Form ◽  
Mean Values ◽  
Quantum Numbers ◽  
Mean Lifetime ◽  
Temperature Dependences ◽  
Quasiclassical Trajectory Calculation ◽  
The Mean ◽  
Combustion Processes

The reaction O + OH → O2 + H in conditions of combustion of hydrocarbons and polymers was modelled by using the method of quasiclassical trajectories. The potential energy surface was determined by the multiconfiguration interaction method and fitted with the analytical form of the extended LEPS function. Attention was paid to the mean values of the vibrational and rotational quantum numbers of O2 molecules and their temperature dependence. The temperature dependence of the mean lifetime of the OOH collision complex was also examined. The calculated rate constants were analyzed and compared with the experimental data over the temperature region of the combustion processes.

Small-scale energy cascade in homogeneous isotropic turbulence

2019 ◽  
Vol 4 (10) ◽  
Author(s):  
Mohamad Ibrahim Cheikh ◽  
James Chen ◽  
Mingjun Wei
Keyword(s):  
Isotropic Turbulence ◽  
Energy Cascade ◽  
Small Scale ◽  
Homogeneous Isotropic Turbulence
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