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Stabilisation of Turbulent Mixing

#1412


Experimental Investigation into Stabilised Properties of Transitional Layers on the Evolution of Turbulent Mixing

Tech Area / Field

  • PHY-NGD/Fluid Mechanics and Gas Dynamics/Physics

Status
8 Project completed

Registration date
01.12.1998

Completion date
05.04.2005

Senior Project Manager
Bunyatov K S

Leading Institute
VNIITF, Russia, Chelyabinsk reg., Snezhinsk

Project summary

The present Project is directed to the experimental investigation of one of the methods for ensuring the delay in evolution (suppression) of turbulent mixing. It is known when the unstationary flow of liquid or gas takes place the contact boundaries separating different density regions are often unstable. This relates to the case when the light matter accelerates the heavier one or the heavy matter is decelerated by the lighter one. If the acceleration is of quasi-steady character, then Rayleigh-Taylor instability develops at the contact boundary [1, 2]. When the acceleration is of pulsed (d-shaped) character, then Richtmyer-Meshkov instability develops. As a result of the instability evolution, the contact boundary between two media is destroyed, the flow is turbulized and it is formed the region (zone) in which the heavy matter and the light one are found in a mixed state.

The problem of hydrodynamic instabilities and turbulent mixing of the interface between different density media during their unstationary motion relates to a number of fundamental classic problems of hydrodynamics. This phenomenon is widely met at the motion of air masses and admixtures in the Earths atmosphere, in the World Ocean, at the evolution of some astrophysical processes and in many technical devices.

At present, it is possible to say that the averaged characteristics of unstationary turbulence have been well studied. The results of the greater part of investigations devoted to this problem have been set in the Proceedings of International Workshops on Compressible Turbulent Mixing beginning from Workshops in Prinston (USA), Cambridge (England) and ending in the Workshop in Marseilles (France). These investigations made possible to determine experimentally and theoretically the growth rate of the mixing zone, the spatial-time distribution of the matter average density in the mix region, coefficient of asymmetry in the evolution of mixing for different Atwood numbers.

At the same time, such an important problem for practical applications as the suppression of turbulent mixing has been slightly studied experimentally, and some approaches have just been outlined. Up to last time it has been considered that if there are conditions for the instability evolution, then at the contact boundary of two different density media the occurrence of turbulent mixing is inevitable. At present, there are indications that it is possible to “fight“ against turbulent mixing. The following has been revealed experimentally. In experiments of Read and Youngs the delay in the turbulent mixing development has been observed. This delay could be determined by reprocessing of experimental results. In Russian Federal Nuclear Center - VNIITF the first experiments directed to the turbulent mixing suppression have been performed. It has been shown that under definite conditions it is possible to organize the delay in the turbulent mixing evolution by means of transitional layers. It may be appeared that the transitional layers usage will make possible to organize any delay in the turbulent mixing evolution. This phenomenon has not been early predicted theoretically (with taking into account nonlinear effects and turbulence). Thereby, the extremely interesting region of investigations opens which is important for many technical applications.

Experimental investigations envisaged by the present Project are directed to the investigation into the stabilizing properties of transitional layers in the evolution of turbulent mixing. The experiments will be prepared and conducted at the installations EKAP, SOM, OSA in RFNC-VNIITF with using X-ray, light and laser methods of the turbulence parameters registration. It is proposed to investigate the stabilizing role of transitional layers on the evolution both of Rayleigh-Taylor and Richtmyer-Meshkov instabilities as well as on the evolution of turbulent mixing. The delay in the turbulent mixing evolution will be determined experimentally. The experimental dependencies of this delay on the transitional layer parameters and the initial perturbations spectrum characteristics at the contact boundary will be obtained. Experiments will be performed with different Atwood numbers.

As a result of the Project fulfillment the following will be done:


A) technology for obtaining continuous density profile layers separating the different density media (liquids and gases) will be developed;
B) techniques for the determination of the transitional layers parameters in liquids and gases will be developed;
C) at the installation EKAP, by means of X-ray technique, the results will be obtained with respect to influence of the transitional layer width and the initial perturbations spectrum on the turbulent mixing evolution induced by Rayleigh-Taylor instability for different Atwood number with the determination of the averaged matter density in the mixture zone;
D) at the installation SOM the “laser sheet” technique will be developed and by means of it the results will be obtained with respect to the influence of the transitional layer width and the initial perturbation spectrum on the turbulent mixing evolution induced by Rayleigh-Taylor instability for different Atwood numbers with the determination of the heterogeneous structure of matter in the mixture zone;
E) at the installation OSA by means of the schlieren-technique the results will be obtained with respect to the influence of the transitional layer width and form as well as the initial perturbations spectrum on the turbulent mixing evolution in gases which is induced by Richtmyer-Meshkov instability for different Atwood numbers and different Mach numbers.

Work being performed under this Project is within the framework of fundamental investigations of turbulent hydrodynamics and conforms to the ISTC goals. The work on the Project will make possible for RFNC-VNIITF scientists and engineers engaged in the development of weapon to apply their knowledge for solving international scientific and technical problems. This will promote to their integration into the international scientific community.


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