A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
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Blast simulation 127<br />
long, <strong>and</strong> a further expansion cone connected this section to a 4.86 m diameter<br />
section 66 m long. This was followed by a semi-circular 10.7 m diameter<br />
extension. The development <strong>and</strong> calibration <strong>of</strong> the simulator has been reviewed<br />
by Tate [6.20] who noted that the guns were removed <strong>and</strong> the blast wave was<br />
eventually generated in the 1.82 m tube by the detonation <strong>of</strong> up to 100 m <strong>of</strong><br />
detonating cord (59 g <strong>of</strong> PETN/m) wound vertically on an exp<strong>and</strong>ed polystyrene<br />
former. The use <strong>of</strong> explosives rather than compressed air meant that the<br />
diaphragms <strong>of</strong> the early small shock tubes were no longer required. The blast<br />
wave shape was found to be very similar to the ‘Friedl<strong>and</strong>er’ shape discussed<br />
earlier (see Figure 1.1), although for economic reasons the larger tubular sections<br />
were shorter in length than would be normally adopted in shock tube work.<br />
The complete facility is shown in Figure 6.3, taken from ref. [6.20].<br />
We have already noted that a rarefaction wave is produced at the open end<br />
<strong>of</strong> a shock tube, <strong>and</strong> considerable research has taken place to support the<br />
development <strong>of</strong> suitable Rarefaction Wave Eliminators (RWE). In the Foulness<br />
tube the eliminators take the form <strong>of</strong> metal grids that give partial blockages at<br />
the open end <strong>of</strong> the final tunnel <strong>and</strong> at the end <strong>of</strong> the 4.86 m diameter section.<br />
The blockage due to the grid at any section is about 40% <strong>of</strong> the total crosssectional<br />
area, <strong>and</strong> Tate points out that a restriction less than this would allow<br />
too strong a rarefaction wave to propagate back into the preceding tube; a<br />
greater restriction would limit the peak pressure attainable in the final semicircular<br />
test section. The ratio <strong>of</strong> the peak instantaneous pressures in the sections<br />
<strong>of</strong> the tube are, to a first approximation, inversely proportional to the ratio <strong>of</strong><br />
the cross-sectional areas. At the time <strong>of</strong> Tate’s paper the peak pressure in the<br />
final semi-circular tube was limited to less than 55 psi.<br />
Figure 6.3 Explosive-driven blast-wave simulator, Foulness, UK (from Tate, ref.<br />
6.20).