Michael Liverts

• PhD
• Associate Professor at KTH Royal Institute of Technology

Convergence of cylindrical shock in argon is studied both experimentally and numerically. Shock tube experiments are conducted, where a planar shock is first transformed to a cylindrical shape and then converged to its focal axis. Numerical simulations of the converging shock using equations of state for an ideal gas and a real gas (SESAME 5173 mod...

Two interacting supersonic water jets and collisions of a water jet with an aluminum target are studied experimentally and by hydrodynamic simulations. Supersonic water jets form, when shocks generated by underwater electrical explosions of conical wire arrays converge. The arrays are supplied by a ∼250 kA, ∼1 μs rise time current pulse. Underwater...

Experimental and magnetohydrodynamic numerical simulation results and analysis of a μs- and sub- μs-timescale overdamped underwater electrical explosion of copper wires having different lengths and diameters are presented. For these explosions, ∼80% of the energy stored in the pulse generator is deposited into the wire during a time comparable or s...

We present the results of the research on underwater electrical explosion of planar copper wire arrays, accompanied by the generation of a planar shock, using the synchrotron-based phase-contrast radiography imaging capabilities of the ID19 beamline at the European Synchrotron Radiation Facility. It is shown that the interaction of a strong shock w...

A supersonic jet of Mach number M = 4.5 in air is produced experimentally at the apex of a miniature 150 x 50 x 5 mm converging section with a 2 x 5 mm opening by the principle of blast wave amplification through focusing. An initial plane blast wave of M = 2.4 in the convergence section is generated by the exploding wire technique. The profile of...

Fibre collection on screens is here used as a collective name for any preferred or non-preferred deposition of fibres, appearing in e.g. paper manufacturing, recycling of elongated particles or equipment clogging. The fibre collection on screens is typically discussed on basis of the application and may distinguish between fibre collection being a...

While conventional shock tubes have a distinct advantage in dynamic calibration methods due to their inherent capability to generate pressure pulses of desired amplitude and fast rise time, they are limited to the lower levels of the pressure amplitude realization range (≤7 MPa). With the increasing need for a traceable dynamic calibration standard...

In this work, temperature measurements at the focus of spherically converging shock waves (CSWs) in argon are revisited. Spherical shock waves are produced inside a conventional circular shock tube, where initially plane shocks are transformed into spherically shaped shocks inside an axisymmetric smoothly converging section. As the CSW reflects fro...

Shock wave propagation through an inclined inhomogeneity is investigated experimentally and numerically. The shock wave is generated by exploding wire technique, and its propagation is captured using shadowgraph technique. The numerical simulation is performed using an in-house code. When a shock wave encounters such a medium, the flow field is no...

The unstable evolution of an elongated elliptically shaped inhomogeneity that is embedded in ambient air and aligned both normal and at an angle to an incident plane blast wave of impact Mach number 2.15 is investigated both experimentally and numerically. The elliptic inhomogeneities and the blast waves are generated using gas heating and explodin...

This project has five specific objectives: To provide traceability for dynamic pressure and temperature through development of measurement standards and validated calibration procedures; To quantify the effects of influencing quantities on the response of dynamic pressure and temperature sensors, in order to determine the appropriate calibration pr...

Most of the investigations on shock wave interacting with a liquid droplet in literature have been on the breakup/shattering of the droplet (Engel [1], Ranger and Nicolls [2], Wierzba and Takayama [3], Joseph et al. [4], Igra and Takayama [5], and Theofanous and Li [6]). The diameter of the droplet used for previous studies had been in the order of...

Converging shock waves generate high energy concentrations at the implosion focus and have been studied since Guderley’s pioneer analytical treatment [1]. The similarity solution for converging cylindrical and spherical shocks describes a continuously accelerating shock with ever-increasing temperature and pressure behind the shock front as it appr...

The mitigation of externally generated strong blast waves by an aqueous foam barrier of varying configurations within fixed distance between the explosion origin and the object to be protected is investigated and quantified both experimentally and numerically. The blast waves of shock Mach number 4.8 at 190 mm from the explosion plane are generated...

A complex system of waves propagating inside a water column due to the impact of plane shock wave is investigated both experimentally and numerically. Flow features, such as, focusing of expansion waves generating large negative pressure,nucleation of cavitationbubbles, and a re-circulation zone are observed and discussed qualitatively and quantita...

Spherical shock wave implosion in argon is studied both theoretically and experimentally. It is shown that as the strength of the converging shock increases the nonideal gas effects become dominant and govern the evolution of thermal and transport gas properties limiting the shock acceleration, lowering the gas adiabatic index and the achievable en...

In this work, we implement an exploding wire technique to generate small-scale cylindrical blast waves in aqueous foam. The exploding wire system offers an easy to operate and effective tool for studying blast-wave/foam interaction related phenomena in real explosion scenarios. The mitigation of blast waves as a function of the thickness of the foa...

Three different approaches to macro-mechanical modeling of blast-wave mitigation in foam namely: the single-phase effective gas flow model, the two-phase mixture model and the single bubble/shock wave interaction model are critically reviewed. The nature and extent of the approximations inherent in the formulation of the first two models were exami...

Multiphase flows, which involve compressible or incompressible fluids with linear or nonlinear dynamics, are found in all areas of technology at all length scales and flow regimes. In this contribution, we discuss application of aqueous-foam barriers against blast wave impact. The first experiments demonstrating this behaviour were conducted in the...

A phenomenological study of the process occurring when a plane shock wave reflected off an aqueous foam column filling the test section of a vertical shock tube has been undertaken. The experiments were conducted with initial shock wave Mach numbers in the range and foam column heights in the range 100-450 mm. Miniature piezotrone circuit electroni...

For many applications where solid and heavy protections against blast are inoperative, the mitigation of the blast wave loading in a cost-effective manner could be achieved using aqueous foam. The protective behavior of aqueous foam is mainly ascribed to high compressibility of the gas bubbles, which is generally accomplished with energy losses due...

Among the materials, which are capable of dissipating or absorbing the blast energy, aqueous foams is a good solution, when the place and the time of the blast are known in advance. If the height and the density of foam barrier are sufficient, the blast energy transmitted to nearby objects and personnel could be reduced to harmless levels. Unfortun...

Blast waves mitigate in foam due to various mechanisms, whose contribution to the final result is not fully understood yet. Actually, blast waves can destroy the foam barrier that is usually prone to decay and thus subsides with time. Fortunately, different time scales allow separating between these processes. The foam shattering, for example, coul...

Dynamic simulation of the smart catalytic converter, proposed by Daimler AG, is presented. The smart catalytic converter combines NOx storage, on-board ammonia production and selective catalytic reduction (SCR) and functions in a dual-mode operation, alternating between lean burn and rich burn. It relies on intrinsic dynamic operation and synchroni...

The effects of coal fly ash dispersed in foams on the coarsening and drainage dynamics are investigated in a free drainage experiment. The growth rate of the bubbles is not significantly changed. The rates of the fluid drainage are significantly slower when powder is present, which cannot be attributed to an increase in the fluid’s viscosity associ...

We present macroscopic experiments that show how the decay phenomenon affects the sound wave mitigation in wet aqueous foams and how both effects depend on the mass concentration of added particles of coal fly ash. To measure the mitigation of a sound wave as a function of the drainage time and particle concentration both a standing-wave and a sing...

It is well established, nowadays, that if the particles added to aqueous foams are hydrophilic, have proper size and shape they concentrate within the Plateau borders and decrease the liquid drainage. The fact that solid additives can increase the protective performances of a particulate aqueous foam is also well known and even patented. This study...

Field-aligned and gyrophase bunched ion beams are observed in the foreshock of the Earth bow shock. One of the mechanisms proposed for their production is non-specular reflection at the shock front. We study the distributions which are formed at the stationary quasi-perpendicular shock front within the same process which is responsible for the gene...

We study the compression driven magnetic reconnection in the relativistic electron-positron plasma. Making use of a 2.5D particle-in-cell code, we simulated compression of a magnetized plasma layer containing a current sheet within it. We found that the particle spectrum within the reconnecting sheet becomes non-thermal; it could be approximated by...

Mobile and easy to use barriers of aqueous foam suppress blast waves as well as the fireball that follows explosion by dissipation mechanisms and/or energy transfer into less destructive forms. Early investigations established that damping the capacity of these barriers depends on a number of factors that include the foam density and the characteri...