| Description |
The study of oscillatory burning here reported employed end-burning grains in a side-vented cylindrical chamber. Supplementary data concerning the visco-elastic properties of the propellant were gathered by means of shock tube tests. The shock tube tests showed that the velocity of sound in the propellant was 5,620 feet per second. These tests also established that, in amplitude, each successive undriven wave in the propellant was about 0.3 times as large as the previous one. Only axial modes of oscillation were observed in the burner and the frequencies of the first mode varied between 260 cycles per second and 3,300 cycles per second. The recorded frequencies were inversely proportional to the length of the gas column opposing the burning propellant surface as would be predicted from acoustical theory. Irregular burning was not observed in any of the tests and the maximum peak-to-peak amplitude of the pressure oscillations was about 25 psi, roughly 13 per cent of the mean chamber pressure. Three propellants were used in the study but only the two polysulfide- ammonium perchlorate propellants exhibited oscillatory burning. The third propellant, a highly aluminized polybutadiene-acrylic acid copolymer and ammonium perchlorate combination showed only very low amplitude, non-acoustical oscillations. |
