Detonations cellular

The nature of the restrictive boundary conditions for detonation is closely related to the cellular stmcture of a detonation wave (Section 3.2.2). It was systematically investigated in a series of flame propagation experiments in obstacle-filled tubes by Lee et al. (1984). The most important results are summarized below ... 

Thus, the elementary cellular structure could be regarded as an intrinsic characteristic of fhe detonation in a mixture at given initial composition, temperature, and pressure. The dimension of X is of fhe order of magnitude of millimeters or less for gaseous mixfures with oxygen, but several centimeters for less sensitive mixtures (even larger, for methane/air af afmospheric pressure). It decreases when the initial pressure increases. Its variation with the initial temperature is more complicated and depends on the value of fhe reduced activation energy of fhe chemical reactions. The value of... 

Example of the failure of the cellular structure at the passage from solid walls to porous walls in the detonation of C2H2 + 2.5O2 mixture at 2.6kPa initial pressure. (Reprinted from Radulescu, M.I. and Lee, Combust. Flame, 131,29,2002. With permission.)... 

V.N. Gamezo, D. Desbordes, and E.S. Oran, Formation and evolution of two-dimensional cellular detonations. Combust. Flame, 116, 154-165, 1999. 

V.N. Gamezo, A.A. VasiTev, A.M. Khokhlov, and E.S. Oran, Fine cellular structures produced by marginal detonations. Proceedings 28th Symposium (International) on Combustion, The Combustion Institute, Pittsburg, PA, 28, pp. 611-617, 2000. 

M.-O. Sturtzer, N. Lamoureux, C. Matignon, D. Desbordes et H.-N. Presles, On the origin of the double cellular structure of the detonation in gaseous nitromethane and its mixtures with oxygen. Shock Waves, 14(1-2), 45-51, 2005. 

In Chapter 8.5, B. Veyssiere exposes the state of knowledge in detonations. Particular features of the complex multidimensional structure of detonations are presented in relation with the recent results obtained either by nonintrusive optical diagnostics or numerical simulations from high performance calculations. The role of transverse waves in detonation propagation, the existence of correlations between the characteristic dimension of the cellular structure and the critical conditions for detonation initiation and detonation transmission, and the influence of the nonmonotonous heat release process behind the front are examined. Recent developments in the study of spinning detonations are also discussed. 

Original studies of gaseous detonations have shown no single sequence of events due primarily to what is now known as the complex cellular structure of a detonation wave. The primary result of an ordinary thermal initiation always appears to be a flame that propagates with subsonic speed. When conditions are such that the flame causes adiabatic compression of the still unreacted mixture ahead of it, the flame velocity increases. According to some early observations,... 

However, there is now evidence that all self-sustaining detonations have a three-dimensional cellular structure. 

F. THE STRUCTURE OF THE CELLULAR DETONATION FRONT AND OTHER DETONATION PHENOMENA PARAMETERS... 

An excellent description of the cellular detonation front, its relation to chemical rates and their effect on the dynamic parameters, has been given by Lee [6], With permission, from the Annual Review of Fluid Mechanics, Volume 16, 1984 by Annual Reviews Inc., this description is reproduced almost verbatim here. 

FIGURE 5.15 End-on pattern from the normal reflection of a cellular detonation on a smoked glass plate (after Lee [2]). 

From both the cellular end-on or the axial fish-scale smoke foil, the average cell size A can be measured. The end-on record gives the cellular pattern at one precise instant. The axial record, however, permits the detonation to be observed as it travels along the length of the foil. It is much easier by far to pick out the characteristic cell size A from the axial record thus, the end-on pattern is not used, in general, for cell-size measurements. 

P. A. Urtiew and C. M. Tarver, Effects of Cellular Structure on the Behavior of Gaseous Detonation Waves under Transient Conditions, in Gasdynamics of Detonations and Explosions, vol. 75 of Progress in Astronautics and Aeronautics, J. R. Bowen, N. Manson, A. K. Oppenheim, and R, I. Soloukhin, eds.. New York American Institute of Aeronautics and Astronautics, 1981, 370-384. 

The ZND concepts consider the structure of the wave to be one-dimensional and are adequate for determining the static parameters fi, P2, Tz, and Pz- However, there is now evidence that all self-sustaining detonations have a three-dimensional cellular structure. 

F. Siructure of the Cellular Detonation Front and Other Parameters... 

Figure 15 shows the pattern made by the normal reflection of a detonation on a glass plate coated lightly with carbon soot, which may be from either a wooden match or a kerosene lamp. The cellular structure of the detonation front is quite evident. If a similarly soot-coated polished metal (or mylar) foil is inserted into a detonation tube, the passage of the detonation wave will leave a characteristic fish-scale pattern on the smoked foil. Figure 16 is a sequence of laser-Schlieren... 

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