Measurement of spectral characteristics of the turbulent mixing zone

Abstract

Experiments with two pairs of gases with different densities with the initial values of the Atwood number A = 0.21 and 0.83 are performed in a multifunctional shock tube. Statistical and spectral characteristics of the mixing zone formed owing to the Richtmyer-Meshkov and Rayleigh-Taylor instability are obtained by the laser sheet technique, and the range of lengths of the main waves in the structure of this zone is determined. Introduction.A large number of models of turbulent mixing caused by the Richtmyer-Meshkov and Rayleigh-Taylor instability have been developed. In addition to k-ε models, they include models of the second and higher levels of closure [1, 2], whose verification and calibration cannot be performed with the use of integral characteristics of mixing (dimensionless mixing velocity and distributions of the mean density of the substance) obtained in laboratory experiments and require experimentally measured spectral characteristics of time-dependent density and velocity in the mixing zone.Statistical and spectral characteristics of the turbulent mixing zone formed under the consecutive actions of the Richtmyer-Meshkov and Rayleigh-Taylor instability were obtained for some time instants in the present work by the laser sheet technique [3] in a multifunctional shock tube (MST) at the Institute of Technical Physics [4]. The spectral characteristics are used to estimate the range of lengths of the main waves in the mixing zone.The structure of the mixing zone of gases with different densities was studied by the laser sheet technique in [5]. The distribution of density of the heavy gas in the laser sheet plane was obtained. A jump in density was found at the boundary between the heavy gas and the mixing zone. This fact contradicted the integral measurements of the density distributions of fluids with different densities, which were performed in [6] by the x-ray technique. Careful calibration of the measurement technique was performed in the present work.1. Arrangement of Experiments. The experiments were performed in a vertical MST with a square inner cross section 138 × 138 mm; the diagram of the shock tube is shown in Fig. 1. The upper part of the MST contains a section filled with an explosive gas mixture, which is a stoichiometric mixture H 2 + 0.5O 2 . This section is separated from the ambient atmosphere and from the remaining part of the MST by membranes 1 and 4 made of a Mylar film 20 μm thick. The membranes are located on grids consisting of thin metallic strings 0.1 mm in diameter; the cell size of the grids is 12 × 12 mm. The heavy and light gases are separated from each other by a membrane 6 made of a nitrocellulose film whose thickness is approximately 1 μm. The membrane is located on a grid composed of thin strong strings with a cell size of 6 × 6 mm. The MST sections are filled with gases having a pressure of 10 5 Pa and a temperature of 293 K. In the first series of experiments, the heavy gas was carbon dioxide (CO 2 ) with a density ρ 2 = 1.98 · 10 −3 g/cm 3 , and the light gas was hel...

Study of spectral characteristics of a homogeneous turbulent flow

“…Other experimental evidence is available that confirms this law. For example, in [10] with the help of the laser sheet technique in a multifunctional shock tube, spectral and statistical characteristics of the mixing zone were obtained that also supported the Kolmogorov -5/3 power law.…”