L. Biamino

An experimental and numerical investigation of the dependency on the initial conditions of the Richtmyer-Meshkov instability

The nonlinear evolution of 2D single-mode Richtmyer-Meshkov instabilities is investigated through experiments in shock tube and numerical simulations. In our shock tube, the interface is materialized by a thin membrane attached to a stereo-lithographed grid. The purpose of this study is to compare experimental and numerical results, verify that using a higher Mach number for the incident shock wave (Misw) than in a previous study [C. Mariani, M. Vandenboomgaerde, G. Jourdan, D. Souffland, and L. Houas, “Investigation of the Richtmyer-Meshkov instability with stereolithographed interfaces,” Phys. Rev. Lett. 100, 254503 (2008)] drastically reduces the deleterious effects of the membrane remnants, explore the effect of a high initial amplitude at the interface on the growth of the perturbation, and understand the lack of roll-up structures in the nonlinear phase of the instability. Using grayscale gradient rather than gray level, a new processing of the raw pictures is developed. Numerical simulations run wi...

Experimental and numerical study of weak shock wave transmissions through minitubes

The aim of this letter is to present an original experimental technique to study weak shock wave in a minitube. Thus, we designed an apparatus that can be connected to any classical shock tube in order to characterize high speed flows induced by the shock wave transmission in minitubes. We proposed appropriated measurements based on high speed strioscopy coupled with pressure sensors. Two minitube diameters are considered: 1.020±0.010 and 0.480±0.010 mm. We realized preliminary experimental and numerical campaigns with an incident shock wave Mach number at 1.12±0.01. The generation of a microshock wave was observable in the two minitubes. For the smallest minitube, we found an attenuation of the strength of the shock wave with a decrease of 1.8% of the Mach number.

Experimental and Numerical Investigation of the Propagation of a Planar Shock Wave into a Cloud of Droplets

Since several decades, the interest to study the interaction between a shock wave and a two phase medium grows. First, the influence on the propagation of a shock wave by a dusty gas then by a medium composed by solid particles were investigated

Generation of Cylindrical Converging Shock Waves in a Conventional Shock Tube

For ever two decades, the IUSTI laboratory has been known for its investigations [1] dealing with the Richtmyer-Meshkov instability (RMI). Experiments concerning the RMI have been performed in conventional shock tubes [2, 3, 4, 5]. All these experiments use a planar shock wave to generate the instability as perfectly as possible. However, the RMI also occurs in the spherical case where the convergence effects must be taken into account. As far as we know, no conventional (straight section) shock tube facility has been used to experimentally study the RMI in a spherical geometry.

Richtmyer-Meshkov Instability in a Cylindrical Geometry Using a Conventional Shock Tube

During the past 20 years, there was considerable amount of analytical, computational, and experimental works dealing with the planar version of the problem of the Richtmyer-Meshkov instability (RMI). However, this problem is often spherical, and so far there have been only few experimental studies in such configuration, except the cases of both shock-accelerated cylinders [1] and spheres [2] which can be categorized under this label. In convergent geometry, the RMI differs from the planar case due to both the geometrical effects on the instability and a different mono-dimensional (1D) motion of the interface itself. Thus, to better understand the dynamics of this instability in convergent geometry and validate models in such configuration, new experimental data are needed. Holder et al. [3] reported laboratory experiments with a convergent shock tube, using a detonable gas mixture to produce a cylindrically convergent shock. Recently, Zhai et al. [4], Apazidis et al. [5], and Biamino et al. [6] have experimentally proven the possibility of generating a converging cylindrical shock wave using a conventional shock tube. Zhai et al. proposed to design a shock tube having a curved wall test section. This specific wall converts a planar shock wave into a cylindrical one. Apazidis et al. have developed a device where the shock wave propagates inside an annular chamber and focuses after its reflection on the end-wall. Biamino et al. have used and implemented the gas lens theory revisited by Vandenboomgaerde and Aymard [7]. This theory was originally proposed by Dimotakis and Samtaney [8]. This work was the first experimental demonstration of the gas lens technique applied to the T80 conventional shock tube of IUSTI. It was shown that a planar incident shock wave propagating in air (Mis = 1.15) which refracts through a specific elliptical air/SF6 interface generates a cylindrical transmitted shock wave in a two-dimensional wedge geometry with a 30° half apex angle. We were able to diagnose the morphing and the focusing of the shock wave. This study constituted the first step toward canonical experiments on the converging RMI in shock tube environment, for which a second interface had to be implemented. Thus, a new two-dimensional wedge test section (15° half apex angle) was designed to accommodate two interfaces: a first air/SF6 interface of elliptical shape to convert the incident planar shock wave into a cylindrical converging one and a second sinusoidal SF6/air interface to study the converging RMI (see Fig. 1). In the present work, the details of this new experimental apparatus were implemented on the T80 shock tube, and the first results are reported. In particular, the evolution process of interfacial structures induced by RMI is shown.

Blast Wave Impact on a Parallelepiped Headed with a Semicylindrical Model Drilled with a Rectangular Cavity

As part of a research program for the protection of people and buildings after an explosion, a series of experiments is carried out. After an explosion in free air, the created blast wave can penetrate into buildings, boats, or underground shelters.

Long Time Observation of the Richtmyer-Meshkov Instability

Richtmyer-Meshkov (RM) instability occurs when a interface separating two fluids of different density is impulsively accelerated in the direction of its normal. It is one of the most fundamental fluid instabilities and is of importance to the fields of astrophysics and inertial confinement fusion. RM instability experiments are normally carried out in shock tubes, where the generation of a sharp, well-controlled interface between gases is difficult, so there is a dispersion in terms of experimental results. The experiments presented here were conducted in a horizontal shock tube where the materialization of the initial interface was achieved by a thin nitrocellulosic membrane (0.5 μm thick) deposited on a stereolithographed grid support, computer-aided designed and constructed with chosen shape and dimensions. As diagnostic, we used laser sheet flow visualization to yield time-motion image sequences of the linear and the non-linear developments of the instability. In previous investigation [1], we have already shown that residual pieces from the membrane constituting the initial interface tend to delay the interpenetration in the light-to-heavy gas configuration and specifically during the linear stage of the interface evolution. In order to reduce these effects in the present experiments, we have increased the strength of the shock wave (Mach~1.5). We have also extended the test section from 0.46 m to 1.5 m which allows the instability to grow further and thus to observe the whole nonlinear phase until the transition to turbulence. The present paper summarizes the results obtained during this study undertaken for air/SF6 and air/He gas combinations (positive and negative Atwood numbers, respectively) in 2D and 3D geometries.