Richtmyer-Meshkov mixing zone study by a multidirectional laser absorption technique.

Abstract

Shock tube experiments have been undertaken in which a shock wave accelerates normally to an interface separating two gases of different densities leading to the formation of a three-dimensional mixing zone between the two gases. Assuming the mixing zone to be homogeneous and weakly dependent on the wall effects, an integrated monodirectional absorption technique had been previously carried out and average temperature and density evolutions were determined within it. But the mixing zone is really deformed by the wall effects and in consequence it is not homogeneous. Thus, to improve the diagnostic technique, the experimental setup has been modified so that the mixing zone is divided into nine identical homogeneous imaginary regions. Temperature and species concentration are determined through each region of the mixing zone by a multidirectional laser absorption technique in order to have some new information on the influence of the wall effects on the Richtmyer-Meshkov instability study in square-cross-section shock tubes. Furthermore, a better accuracy in the measurements of the mixing zone thickness is obtained from a discussion of the concentration profiles. The consequence is that previous results achieved with integrated techniques such as global Schlieren, shadograph, or monodirectional absorption methods seem to be strongly overestimated.