Turbulizing Chambers along the Tube

The results showed that for the fuel concentration Cf = 0.012, the DDT process did not take place at all. The galloping combustion mode was established and was characterized by velocity oscillations within the range from 80 to 300 m/s, with an average flame-front velocity of 156 m/s. The calculated maps of density and velocity for successive times in the section of the tube incorporating chambers number 6 and 7 are shown in Fig. 4.3. 

The results of numerical experiments showed that increasing the number of turbulizing chambers did not promote DDT for the present configuration, but did just the opposite — it prevented the onset of detonation and brought to establish the galloping combustion mode. The effect is due to very sharp variations in the cross-section area in the chambers and periodic flame slowing down due to its expansion. 

To characterize the cross-section area variation within the structures of such a type, one could use the expansion-ratio and the volume-ratio parameters  

To investigate the influence of the expansion ratio on the onset of detonation, a set of numerical experiments was carried out on the DDT in tubes with diameters of 

3 and 76.7 mm, which had similar chambers 100 mm in diameter and 100 mm long. These two cases correspond to / er values of 60% and 40%, respectively. The tube had 10 chambers distributed uniformly with 50-millimeter intervals, thus the whole structure was 1.45 m long. Comparison of the results (Fig. 4.4) shows that for high values of the expansion ratio, low- 

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