On mixing enhancement by secondary baroclinic vorticity in a shock–bubble interaction

To investigate the intrinsic mechanism for mixing enhancement by variable-density (VD) behaviour, a canonical VD mixing extracted from a supersonic streamwise vortex protocol, a shock–bubble interaction (SBI), is numerically studied and compared with a counterpart of passive-scalar (PS) mixing. It is meaningful to observe that the maximum concentration decays much faster in a VD SBI than in a PS SBI regardless of the shock Mach number ( $Ma=1.22 - 4$ ). The quasi-Lamb–Oseen-type velocity distribution in the PS SBI is found by analysing the azimuthal velocity that stretches the bubble. Meanwhile, for the VD SBI, an additional stretching enhanced by the secondary baroclinic vorticity (SBV) production contributes to the faster-mixing decay. The underlying mechanism of the SBV-enhanced stretching is further revealed through the density and velocity difference between the light shocked bubble and the heavy ambient air. By combining the SBV-accelerated stretching model and the initial shock compression, a novel mixing time estimation for VD SBI is theoretically proposed by solving the advection–diffusion equation under a deformation field of an axisymmetric vortex with the additional SBV-induced azimuthal velocity. Based on the mixing time model, a mixing enhancement number, defined by the ratio of VD and PS mixing time further, reveals the contribution from the VD effect, which implies a better control of the density distribution for mixing enhancement in a supersonic streamwise vortex.

AiStudy on the Behavior of an Underwater Explosion Bubble near a Rigid Wall

The dynamic approach to an underwater explosion (UNDEX) is a complex episode that involves shockwave propagation, bubble pulse with high pressure, and water jet impact. This paper proposes linkage of Finite Element Avenue (FEM) and Companion of Eulerian-Lagrangian (CEL) to supply promised data of large deformations and flow simulation of fluid and gas where the bubble interaction is near a stiff wall. To conduct the process, a 7.5 m x 9.0 m Eulerian domain and explosive charges of 10 g, 35 g, and 55 g TNT are built in a free field, respectively. Numerical analysis, as far as a comparison with research from E. Klaseboer, has been given in this study. The important results obtained from the CEL approach imply high expectations. In spite of the fact that this approach is not adequately consistent to totally supplant a live test, it can be utilized as an outline database to anticipate outcomes of managing an UNDEX with a high pressure bubble. The behavioral explosion from an UNDEX bubble near a rigid wall is a prospective contribution in this research. With these results, this technique can be used in further studies to examine UNDEX bubbles in the vicinity of deformable and complex structures.

Multibubble Sonoluminescence from a Theoretical Perspective

In the present review, complexity in multibubble sonoluminescence (MBSL) is discussed. At relatively low ultrasonic frequency, a cavitation bubble is filled mostly with water vapor at relatively high acoustic amplitude which results in OH-line emission by chemiluminescence as well as emissions from weakly ionized plasma formed inside a bubble at the end of the violent bubble collapse. At relatively high ultrasonic frequency or at relatively low acoustic amplitude at relatively low ultrasonic frequency, a cavitation bubble is mostly filled with noncondensable gases such as air or argon at the end of the bubble collapse, which results in relatively high bubble temperature and light emissions from plasma formed inside a bubble. Ionization potential lowering for atoms and molecules occurs due to the extremely high density inside a bubble at the end of the violent bubble collapse, which is one of the main reasons for the plasma formation inside a bubble in addition to the high bubble temperature due to quasi-adiabatic compression of a bubble, where “quasi” means that appreciable thermal conduction takes place between the heated interior of a bubble and the surrounding liquid. Due to bubble–bubble interaction, liquid droplets enter bubbles at the bubble collapse, which results in sodium-line emission.