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 model) are conducted and compared. High temporal resolution data of cylindrical shock convergence is presented. When comparing the trajectories of the converging shock of initial shock Mach number (M-S) of 4.63, the convergence exponent (alpha) in experiments is found to be 0.833. This alpha value in experiments is higher than the value obtained from computations with argon treated as an ideal gas but agrees well with the real gas computations. It is revealed that the form of convergence varies with different M-S. An asymptotic approach of alpha toward the self-similar solution for high M-S is attributed to an earlier transition of shock motion to self-similarity, while a significantly higher alpha observed at lower M-S is attributed to the negative influence of upstream nonuniformities and weaker initiation of the shock. It is found that even before the shock reflection, real gas effects are significant enough to affect the convergence of the shock and limit the extreme conditions predicted by the ideal gas computations. For an M-S of 4.63, the maximum temperature reached is 9250 K before reflection, leading to 0.12% of the argon gas undergoing the first stage of ionization.

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 similar to 250kA, similar to 1 mu s rise time current pulse. Underwater explosion of two conical arrays placed face to face produces jets propagating in air with velocities of similar to 2.5 x 10(3) m/s leading to hot plasma formation at a temperature of similar to 2200-3000 K, pressure similar to 1.7 x 10(10) Pa, and density > 10(29) m(-3). When a single array explodes underwater in front of an aluminum target, the collision of the jet with the target produces a local pressure of similar to 3 x 10(10) Pa on the surface of the target.

Experimental and magnetohydrodynamic numerical simulation results and analysis of a mu s- and sub-mu s-timescale overdamped underwater electrical explosion of copper wires having different lengths and diameters are presented. For these explosions, & SIM;80% of the energy stored in the pulse generator is deposited into the wire during a time comparable or shorter than a quarter period of the underdamped discharge. It was found that the threshold values of the deposited energy density, energy density rate, and energy density per unit area, which satisfy overdamped discharge, depend on the wire parameters and on the timescale of the explosion. It was shown that the mechanism responsible for this is the process during which the wire experiences phase transitions to a low-ionized plasma, the resistivity of which is determined by the electron-neutral collision rate, which, in turn, depends on the wire radial expansion velocity, current density, and temperature.

This paper presents the main results and achievements of the EMPIR DynPT project [1]. Dynamic measurement of pressure and temperature are a key requirement for process control in several demanding applications, such as automotive, marine and turbine engines, manufacturing processes, and ammunition and product safety. The quality of these measurement has been significantly improved in this project through development of dynamic measurement standards and methods and characterized sensor technologies and means of estimating measurement uncertainties in real process conditions.

The study of the properties of matter at extreme conditions (>109 Pa, >104 K0) is imperative for understanding phenomena where such states are reached in planetary astrophysics and confined fusion. To achieve such states of matter, what is often described as warm dense plasma, extremely high energy density deposition should be realized. One of the techniques used to explore matter under extreme conditions is the underwater electrical explosion of wire and wire arrays accompanied by the generation of strong shock waves. 

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 with an air-water interface leads to additional acceleration of the wire expansion due to a rarefaction wave along with the emergence of micro-jets. In the case of a target placed above the array, we observed the formation of a cavity between the array and the target due to the interaction of two rarefaction waves. The results of two-dimensional hydrodynamic simulations of the wire explosion and the interaction of the generated shock with the water-Air and water-Target interfaces showed good agreement with experimental results. 

This study delves into the modelling of resistance wire thermometers (RWTs) within the applicationcontext of measuring the exhaust gas temperature pulse in internal combustion engines. The modelwas developed in a commercial simulation software utilizing the heat balance equation. Disparitieswere found between different model representations of the prongs due to differences in the heat transfer within the sensor, which impacts its expected dynamic response. The appropriate modelling choicewill be made upon validation with shock tube experiments for different RWT designs

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 friend or foe of the process of interest. We report an extensive experimental investigation of fibre collection and provide a systematic discussion based on two parameters describing the screen geometry: the fibre length to the screen opening size (L-Fibre/D-Open), and fibre length to the distance between the openings (L-Fibre/S-Open). The first parameter, L-Fibre/D-Open, discriminates between the two fibre collection modes: (i) fibre retention (L-Fibre/D-Open, for example paper forming) and (ii) fibre stapling (small L-Fibre/D-Open, for example deposition on pins and edges). The second parameter L-Fibre/S-Open controls the fibre collection rate for both modes (with higher collection rates for higher values), but through different physics. In fibre retention, the successful collection is probabilistic and large for small screen openings and a fibre-orientation parallel to the screen. Since a decrease of L-Fibre/S-Open results in a smaller open area and hence to higher acceleration of the suspension upstream of the screen, the fibre orientation is skewed towards a screen normal orientation and fibres tend to pass through the holes. In the case of fibre stapling, the successful collection comes from an immobilization of the fibre when fibre-solid friction force exceeds the hydrodynamic drag force for fibres deposited close to the edge of the holes. For L-Fibre/S-Open above 1 a fibre bends over the solid hole spacing and is fixated on two support points. For L-Fibre/S(Open )below 1 restrains a successful fibre fixation on two support points why fibre collection on the solid screen is hindered and prevented. The impact of the approach velocity and fibre concentration on the fibre collection was tested and found to be negligible for fibre retention but impacting fibre stapling. This is in agreement with reports on equipment clogging in cellulose fibre processing. For fibre retention, the collection rate is high and close to total retention. However, the collection rate of stapling is much lower. At high velocities, we suggested that fibre bending can cause additional leakage through the screen.

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 the convergence section is specially tailored to smoothly transform a plane blast wave into a perfectly cylindrical arc, imploding at the apex of the section. The cylindrical form of the imploding shock delivers maximum shock amplification in the two-dimensional test section and maximum subsequent jet flow velocity behind the shock front. Blast wave propagation in the convergence chamber as well as jet generation through a 2 mm opening at the apex into the adjacent exhaust chamber is optically captured by a high-speed camera using the shadowgraph method. Visualizing the flow provided a distinct advantage not only for obtaining detailed information on the flow characteristics but also for validating the numerical scheme which further enhanced the analysis. Experimental images together with the numerical analysis deliver detailed information on the blast wave propagation and focusing as well as subsequent jet initiation and development. One of the main advantages of the described method apart from being simple and robust is the effective focusing of low initial input energy levels of just around 500 Joules, resulting in production of supersonic jets in a small confined chamber.

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 across wider pressure ranges, a novel technique using converging shock waves is demonstrated in this work that pushes the upper limit of the standard shock tube into the medium-high pressure range. The experiments are conducted in the shock tube facility equipped with a test section that smoothly transforms the incident plane shock into a spherical shock wave that converges, accelerates and thereby amplifies its strength many folds. The experimentally recorded pressure traces are compared with numerical simulations performed by an in-house code. Using this technique, pressure pulses with peak amplitudes in the range of 30-40 MPa, with <<i 3.4% uncertainty based on numerical reference profile, were realized in the test section with nominal usage of resources.