Effect of geometry on the transmission of detonation through an orifice

Abstract

An experimental study has been carried out to investigate the transmission of a planar detonation wave through an orifice into an unconfined medium. Mixtures of 2H 2 + O 2 + βN 2 and C 2H 4 + 3(O 2 + βN 2) for a range of nitrogen concentrations corresponding to 1 ≤ β ≤ 3.76 and at an initial presure of 1 atm were used in the experiments. It is found that the critical diameter for the transmission through an orifice is identical to that for a straight tube and both follow the empirical correlation of d c ≅ 13 λ. The transmission through square, triangular, elliptical, and rectangular orifices has led to the development of a correlation based on the effective diameter similar to the case of circular geometry (i.e., d eff ≅ 13 λ). The effective diameter is defined as the mean value of the longest and shortest dimensions of the orifice shape. The effective diameter correlation suggests that the criterion for transmission may be based on the mean curvature of the wave front, the implication being that it is not to exceed a certain critical value. The results suggest that local properties in the immediate vicinity of the wave front are the controlling parameters for reinitiation rather than the properties of the gas dynamic flow structure in the wake. Expressions are developed to provide estimates for the critical transmission dimensions for arbitrarily shaped openings. For the two-dimensional limit when one of the characteristic linear dimensions becomes very large compared to the other, it is found that the transmission is based on a critical value for the shorter dimension of the order of 3 times the cell diameter. This result is in accordance with the recent large scale experiments of Benedick in two-dimensional channels of an aspect ratio L.W as large as 35. These observed results can also be successfully explained in terms of the critical wave curvature criterion.