A theoretical model of the shock wave from a lightning discharge ranging from the strong blast wave region out to the acoustic limit is given for the first time. The trajectory and overpressure of the strong shock wave are described by the well-known equations for cylindrical blast waves. In the intermediate shock strength region (1.1 < M < 3.3), the shock trajectory is given by the ‘correct limit’ equation of Vlases and Jones. We derive an additional ‘correct limit’ equation for overpressure that is valid out to the acoustic limit. The correct limit equations predict a much slower decay of the intermediate shock wave; thus, the shock wave is much stronger at large distances from the discharge than was previously believed. Consequently, the range of action of the lightning discharge via its shock wave, as it affects the shattering and freezing of supercooled hydrometeors, may be large.

Shock wave from a lightning discharge

Physics of meteor generated shock waves in the Earth’s atmosphere : A review

The technology of wire explosion has been used to produce nanopowders. A new concept was proposed to produce nanosized powder, which is wire explosion in liquid media. We have exploded the Ag wires with 0.3-mm diameter and 25-mm length, in the de-ionized water. Electrical energy of 1.1 kJ was stored in a 10-uF capacitor and released to the wires through a triggered spark gap switch. The process was observed by high-speed camera. Those images showed that the powders were generated by vapor condensation in the shell formed by the shock wave in the water. The particles were directly dispersed into the water with the collapse of the shell. The pure Ag nanopowder was produced by this method.

Production of nanopowders by wire explosion in liquid media

Experimental measurements are given for the energy input and shock wave arrival times for 10‐cm No. 40 Cu wires exploded in air at an initial voltage of 9.25 kv. Two shocks in air are observed, one for each pulse before and after the dark pause. Pause duration measurements are also reported for wire explosions in gaseous He, N2, O2, Ar and CClF3 at l atm. Semiquantitative theoretical explanations are proposed for the increase in wire resistance which terminates the first current surge, and for the elapsed time (pause duration) before the vapor density of the expanding wire material declines sufficiently for reignition of the discharge.

On the Mechanism of Exploding Wires

An experimental study of pressure waves generated by an exploding copper wire in a water medium is performed. We examined the effects of energy deposited at different stages on the characteristics of the resulting shock waves. In the experiments, a microsecond time-scale pulsed current source was used to explode a 300-μm-diameter, 4-cm-long copper wire with initial stored energies ranging from 500 to 2700 J. Our experimental results indicated that the peak pressure (4.5–8.1 MPa) and energy (49–287 J) of the shock waves did not follow a simple relationship with any electrical parameters, such as peak voltage or deposited energy. Conversely, the impulse had a quasi-linear relationship with the parameter Π. We also found that the peak pressure was mainly influenced by the energy deposited before separation of the shock wave front and the discharge plasma channel (DPC). The decay time constant of the pressure waveform was affected by the energy injection after the separation. These phenomena clearly demonstra...

Relationship between energy deposition and shock wave phenomenon in an underwater electrical wire explosion

A simple technique has been found for rendering visible the shock wave formed by an exploding wire after the shock has separated from the luminous contact surface. A small, plane mirror is placed just behind the wire so as to be perpendicular to the axis of the optical system. Thus the reflected image of the wire explosion coincides with the disturbance itself when seen through the slit by the camera lens. Rotating mirror pictures taken under these conditions show very clear outlines of the parabolic shock wave as it propagates ahead of the luminous contact surface. The separation of the shock and contact surface is complete by about one μsec. Beyond this time the shock is clearly nonluminous and ordinarily would not be visible. Comparison of shock trajectories with predictions from the similarity solutions for strong shock waves obtained by S. C. Lin may be interpreted as showing that the shock is receiving additional energy while traversing the early part of its path. After this phase both shock and contact surface accurately obey a parabolic law over intervals of several microseconds.

F. D. Bennett

Papers

Cylindrical Shock Waves from Exploding Wires