Detonation limits in rough walled tubes

Abstract

The present paper reports the results of a study of detonation limits in rough tubes. Detonation velocity is measured by photodiodes and ionization probes spaced at 10cm intervals along the length of the tube. Short lengths of smoked foils inserted into the core of the rough tube is used to register the structure of the detonation wave. Pressure transducers are also used to obtain the pressure profile. The results indicate that in rough tubes, the detonation velocity is generally much lower than the corresponding values for smooth tubes. The velocity decreases slowly at first and then more rapidly as the limit is approached. The velocity variation is generally continuous and at the limits, the failure velocity is of the order of about 0.4 VCJ for all cases. The detonation limits in rough tubes are found to be wider than for a smooth tube. This indicates that the turbulence generated by the wall roughness facilitates the propagation of the detonation and extends the limits. Smoked foil records show that in the core of the rough tube the detonation front has a cellular structure corresponding to the usual cellular structure due to instability of the detonation. Thus the intrinsic unstable cellular structure is quite robust and retains its global characteristics in spite of the large perturbations generated by the rough wall. The detonation in the core of the rough tube goes from multi-headed to single headed as the limit is approached. Past the single headed spin, the low velocity detonation has no cellular structure but consists of interacting weak transverse waves from the rough wall. The averaged pressure of the low velocity detonation front corresponds to about the constant volume explosion pressure, in accord with the velocity of the low velocity detonation.