510 / 2019-03-19 11:16:33

Development of a three-dimensional gas cylinder under reshock conditions

Richtmyer-Meshkov instability,Shock wave,Reshock,Gas cylinder

全体主题 > Interface Instabilities at Extremes

When an initially perturbed interface separating two fluids of different properties is impulsively accelerated by a shock wave, perturbations initially imposed on the interface will experience successively linear and nonlinear growth, and eventually trigger the turbulent mixing. This type of interfacial instability is usually regarded as Richtmyer-Meshkov instability (RMI). The RMI has been the subject of intensive research due to its significance in compressible turbulence and inertial confinement fusion. In study of the RMI, much attention has been paid to the generation of an initial interface with well-characterized perturbations. Among the initial interfaces previously reported, spherical and cylindrical configurations are fundamental ones as they cover the complete range of angles between the pressure and density gradients, which would affect the distribution of baroclinic vorticity deposited on the interface. Recently, the interactions of a planar shock with three-dimensional (3D) heavy (SF6) and light (Helium) gas cylinders have been successfully realized in shock tube experiments and the results demonstrated that the initial interface curvature significantly affects the flow morphology, wave pattern, vorticity distribution and the interface movement. As for a gas cylinder, the influence of the three-dimensionality on the flow structure would be much different from the two-dimensional (2D) case. Moreover, the corresponding late-time turbulent mixing would be much more chaos than the 2D counterpart due to the 3D vortex associated with the initial interface curvature. Moreover, as the reshock from the end wall arrives at the distorted interface, the phenomena will be distinct, which motivates the present work.
In the present study, the circular wire-restriction method with soap film technique developed in our group is extended to form 2D and 3D heavy gas cylinders. In experiments, the initial interface as well as the incident planar shock and the reshock can be well captured by the high-speed schlieren diagnostics, demonstrating the feasibility and reliability of the experimental method. The initial interface before the shock impact seems much thicker than that in the 2D case because of the integrated view of the interface convex/concave shape. The interface borders at symmetry and boundary slices can be identified by the inner and outer contours of the schlieren pictures, respectively. It can be seen that in the whole evolution process, the structure of the convex cylinder is distinct from the 2D counterpart and presents a remarkable 3D effect, which would trigger the flow transition to turbulent mixing in a relatively shorter time than the 2D counterpart. The present work would provide underlying physical mechanism of RMI flow transition and induced turbulent mixing.