Reflected Detonation Wave Parameters

Apart from a normal reflection of a detonation wave, various interactions with obstacles can occur in a real situation. Work [6] gave an example and analyzed a detonation wave going out of a duct to a large space restricted by walls. At first, development of a spherical detonation was recorded (time t t2 h  

The diagram in Fig. 7.7 demonstrates the dependence of the pressure rise of the reflected detonation wave on the angle of incidence 6. The ratio of (pressure behind the reflected wave) to P2 (pressure at the C-J point behind the detonation wave) is plotted on the y-coordinate. The vertical line plotted at 0 57° separates 

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The laser interferometry technique is widely used for the study of the detonation wave time profile and structure due to its exceptionally good time resolution. The laser interferometry operating principle is based on the Doppler effect. The technique records the position and time dependence of the interferometric fields obtained due to the Doppler shift in wavelength of the reflected laser beam, resulting from the thin metal shim motion. The metal shim, 15-25 pm thick, is placed between the explosive charge and windows that are made of an inert optically transparent material, such as water, lithium fluoride, or polymethylmethacrylate. On the basis of the velocity of the explosive/metal shim interface as a function of time, it is possible to calculate the values of detonation parameters of the explosive (Gimenez et al., 1985, 1989 Hemsing, 1985 Leeetal., 1985). 

The maximum pressure occurring at the moment of reflection can be computed from the Rankine-Hugoniot equations without taking account of the expansion wave. Those computations are analogous to those used for the more usual nonreactive shock reflection. Computations with realistic thermodynamics were carried out with a modified version of the STAN JAN code. The resulting reflected detonation parameters are given in Table 1. 

Figure 10.21 illustrates the change in the Kp value with distance for a reflected blast wave (curve 1) and an incident blast wave (curve 2) for Ef = 46 MJ/kg. Figure 10.22 presents similar relations for the TNT impulse equivalent Kp Comparison between parameters of incident, reflected and rarefaction waves resulting from gas detonations and HE charge explosions shows that the similarity... 

Finally from the space-time diagrcun of the incident pressure wave, which depends on the two parameters X and E, and simultaneously from the modeled pressure load of the reflected wave on a plane surface that only depends on X, it is possible to predict the dynamic loading Ap(t) at any point on the plane surface. In Fig. 11 the predicted arrival times tai and the observed ones texp collected from numerous experiments are compared. The scattering does not exceed 10%. In Fig. 12 the effective measured pressures and the predicted ones on a wall located near the hemispherical detonating charge are compared. The agreement is excellent. 

The TNT pressure Kp and impulse Kj. equivalents can be assessed based on the comparison between parameters of reflected and incident waves resulting from a HE charge explosion and a gas detonation. 

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