scholarly journals Experimental study of the influence of the stabilizing properties of transitional layers on the turbulent mixing evolution

2003 ◽  
Vol 21 (3) ◽  
pp. 369-373 ◽  
Author(s):  
Yu.A. KUCHERENKO ◽  
S.I. BALABIN ◽  
R.I. ARDASHOVA ◽  
O.E. KOZELKOV ◽  
A.V. DULOV ◽  
...  
Keyword(s):  
Diffusion Layer ◽  
Turbulent Mixing ◽  
Molecular Diffusion ◽  
Mixing Layer ◽  
Mixing Zone ◽  
Transitional Layer ◽  
Diffusion Layer Thickness ◽  
X Ray ◽  
Rayleigh Taylor Instability ◽  
Miscible Liquids

Experiments conducted on the EKAP facility at the Russian Federal Nuclear Center–VNIITF concerning the stabilization of Rayleigh–Taylor instability-induced mixing in miscible liquids by the formation of a molecular diffusion (or transitional) layer between the liquids initially were described. The experiments had an Atwood number of 1/3. The acceleration was 3500 times that of Earth's gravity, and several values of diffusion layer thickness were considered. The experiments showed that the growth of the turbulent mixing zone could be delayed by adjusting the amplitude of the initial perturbations and the characteristic thickness of the diffusion layer. This has been observed in experiments conducted with water and mercury. The mixing layer evolution was imaged using X-ray radiography.

scholarly journals Experimental investigation into inertial properties of Rayleigh–Taylor turbulence

1997 ◽  
Vol 15 (1) ◽  
pp. 25-31 ◽  
Author(s):  
Yu.A. Kucherenko ◽  
S.I. Balabin ◽  
R. Cherret ◽  
J.F. Haas
Keyword(s):  
Experimental Investigation ◽  
Kinetic Energy ◽  
Turbulent Mixing ◽  
Average Density ◽  
Taylor Instability ◽  
X Ray ◽  
Two Fluids ◽  
Time Space ◽  
Rayleigh Taylor Instability ◽  
Region Size

An experimental investigation into inertial properties of the developed Rayleigh–Taylor instability with the different initial values of the kinetic energy of turbulence has been performed. The experiments were performed by using two fluids having different densities with density ration n = 3. Fluids were placed in an ampoule. At the unstable stage of motion, the ampoule was moving under an acceleration. At a certain instant of time the acceleration was removed and the ampoule moved under the force of inertia. By means of pulsed X-ray photography, the mixing region size and the time-space distributionof the average density of matter in the turbulent mixing region have been determined at different instants of time. The time-space distributions are compared with those obtained by semiempirical theories of mixing.

Strain and Stratification Effects on the Rapid Acceleration of a Turbulent Mixing Zone

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Benoît-Joseph Gréa ◽  
Jérôme Griffond ◽  
Fabien Godeferd
Keyword(s):  
Turbulent Mixing ◽  
Density Field ◽  
Moving Frame ◽  
Mixing Zone ◽  
Mean Flow ◽  
Time Dynamics ◽  
Rayleigh Taylor Instability ◽  
The Mean ◽  
Two Parameters ◽  
Short Time

We consider the problem of a turbulent mixing zone (TMZ), initially submitted to coupled effects of axisymmetric strain and stratification, then subsequently accelerated. The TMZ grows in the latter stage due to a rapid mixing induced by the Rayleigh-Taylor instability. It is shown that the short time dynamics is simply determined by only two parameters expressing the structure of the turbulent density field, one related to the mixing, the other to the dimensionality of the flow. These quantities are studied by rapid distortion theory and by several homogeneous direct numerical simulations performed in the moving frame of the mean flow. The implications for modeling are discussed, the influence of anisotropy is presented.

scholarly journals Experiments and Simulations on the Turbulent, Rarefaction Wave Driven Rayleigh–Taylor Instability

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
R. V. Morgan ◽  
J. W. Jacobs
Keyword(s):  
Rarefaction Wave ◽  
Lawrence Livermore National Laboratory ◽  
National Laboratory ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Quantitative Agreement ◽  
Diffuse Interface ◽  
Diffusion Layer Thickness ◽  
Average Value ◽  
Rayleigh Taylor Instability

Abstract Experiments were performed to observe the growth of the turbulent, Rayleigh–Taylor unstable mixing layer generated between air and SF6, with an Atwood number of A=(ρ2−ρ1)/(ρ2+ρ1)=0.64, where ρ1 and ρ2 are the densities of air and SF6, respectively. A nonconstant acceleration with an average value of 2300g0, where g0 is the acceleration due to gravity, was generated by interaction of the interface between the two gases with a rarefaction wave. Three-dimensional, multimode perturbations were generated on the diffuse interface, with a diffusion layer thickness of δ=3.6 mm, using a membraneless vertical oscillation technique, and 20 experiments were performed to establish a statistical ensemble. The average perturbation from this ensemble was extracted and used as input for a numerical simulation using the Lawrence Livermore National Laboratory (LLNL) Miranda code. Good qualitative agreement between the experiment and simulation was observed, while quantitative agreement was best at early to intermediate times. Several methods were used to extract the turbulent growth constant α from experiments and simulations while accounting for time varying acceleration. Experimental, average bubble and spike asymptotic self-similar growth rate values range from α=0.022 to α=0.032 depending on the method used, and accounting for variable acceleration. Values found from the simulations range from α=0.024 to α=0.041. Values of α measured in the experiments are lower than what are typically measured in the literature but are more in line with those found in recent simulations.

scholarly journals Coefficient of heterogeneity in turbulent mixing zone

2000 ◽  
Vol 18 (2) ◽  
pp. 207-212 ◽  
Author(s):  
A.S. KOZLOVSKIH ◽  
D.V. NEUVAZHAYEV
Keyword(s):  
Turbulent Mixing ◽  
Molecular Diffusion ◽  
Reynolds Numbers ◽  
Mixing Zone ◽  
Turbulent Diffusion Coefficient ◽  
Dissipative Term ◽  
Developed Turbulence ◽  
Self Similar Solution ◽  
Self Similar ◽  
Good Agreement

The paper considers the equation for heterogeneity coefficient within the turbulent mixing area in the approximation of big Reynolds numbers and small Mach numbers. A mechanism is studied of the heterogeneity coefficient dissipation due to molecular diffusion. The Kolmogorov's hypothesis on developed turbulence is used to calculate a dissipative term. The model presented allows us to take into account the heterogeneity degree in LV- and KE-models of turbulent mixing. A system of equations allowing us to calculate directly the heterogeneity degree is derived for the case of the LV-model with the turbulent diffusion coefficient which is constant over the turbulent mixing area. A self-similar solution is derived for the heterogeneity coefficient which is in good agreement with the results of experiments and direct numerical simulations. The heterogeneity coefficient averaged over the mixing area is shown to depend weakly on the density drop between the mixing materials. Thus, it is kH = 0.25 at the drop n = 1–3, and at the drop n = 20 − kH = 0.23.

A model of constant-flow ventilation in a dog lung

1988 ◽  
Vol 64 (5) ◽  
pp. 2150-2159 ◽  
Author(s):  
E. Ingenito ◽  
R. D. Kamm ◽  
J. W. Watson ◽  
A. S. Slutsky
Keyword(s):  
Gas Exchange ◽  
Turbulent Mixing ◽  
Molecular Diffusion ◽  
Peripheral Zone ◽  
Semiempirical Model ◽  
Mixing Zone ◽  
Constant Flow ◽  
Specific Impedance ◽  
Cardiogenic Oscillations ◽  
Predicted Values

A semiempirical model of constant-flow ventilation (CFV) is developed to test the hypothesis that a three-zone serial model with the following characteristics can explain the adequate CO2 transport observed during CFV: 1) a zone of jet recirculation immediately downstream of the catheter in which convection dominates; 2) a zone influenced by turbulence but with little or no bulk flow; and 3) a peripheral zone, free of turbulence, in which transport is governed by molecular and augmented diffusion. Interactions between turbulent eddies and cardiogenic oscillations are included using a modification of Taylor dispersion theory according to the formulation of Kamm et al. Predicted values for arterial PCO2 are reasonably similar to experimental results for He-O2, air, and SF6-O2 mixtures for catheter flow rates from 0.2 to 1.6 l/s. Specific impedance to gas exchange was found to be largest immediately proximal to the end of turbulent mixing zone, where transport is governed by low-level eddy mixing and molecular diffusion. Simulations suggest that, during CFV, cardiogenic oscillations augment gas exchange primarily by promoting turbulent eddy dispersion in the distal airways and by extending the length of the turbulent mixing zone. Even small displacements of the catheter are shown to have a dramatic effect on gas exchange.

scholarly journals Experimental investigation into the evolution of turbulent mixing of gases by using the OSA facility

2003 ◽  
Vol 21 (3) ◽  
pp. 389-392 ◽  
Author(s):  
Yu.A. KUCHERENKO ◽  
O.E. SHESTACHENKO ◽  
Yu.A. PISKUNOV ◽  
E.V. SVIRIDOV ◽  
V.M. MEDVEDEV ◽  
...  
Keyword(s):  
Growth Rate ◽  
Turbulent Mixing ◽  
Soap Film ◽  
Mixing Zone ◽  
Russian Federal Nuclear ◽  
Liquid Soap ◽  
Compressed Gas ◽  
Rayleigh Taylor Instability ◽  
Schlieren Photography ◽  
Mixing Of Gases

Experiments conducted at the OSA shock tube facility at the Russian Federal Nuclear Center–VNIITF to investigate the compressible turbulent mixing of argon and krypton gases induced by the Rayleigh–Taylor instability are described. A liquid soap film membrane of thickness ∼1 micrometer embedded in an array of microconductors is used, on which specified initial perturbations can be applied. The shock is piston driven by compressed gas. The gas interface was accelerated with an acceleration g′4 3104 m0s2. The membrane is disintegrated at the beginning of the experiment by a strong electric explosion. Imaging is performed using Schlieren photography. The dimensionless growth rate of the mixing zone was determined to be 0.04.

scholarly journals Simulations of the Formation and X-ray Emission from Hot Bubbles in Planetary Nebulae

Galaxies ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 80
Author(s):  
Jesus Toalá ◽  
S. Arthur
Keyword(s):  
Numerical Simulations ◽  
Turbulent Mixing ◽  
Mixing Layer ◽  
Planetary Nebulae ◽  
Magellanic Clouds ◽  
Small Range ◽  
High Quality ◽  
Turbulent Mixing Layer ◽  
X Ray ◽  
Material Form

High-quality X-ray observations of planetary nebulae (PNe) have demonstrated that the X-ray-emitting gas in their hot bubbles have temperatures in the small range TX = (1 − 3) × 106 K. However, according to theoretical expectations, adiabatically-shocked wind-blown bubbles should have temperatures up to two orders of magnitude higher. Numerical simulations show that instabilities at the interface between the hot bubble and the nebular material form clumps and filaments that generate an intermediate-temperature turbulent mixing layer. We describe the X-ray properties resulting from simulations of PNe in our Galaxy and the Magellanic Clouds.

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