Nonacoustic (low-frequency) instability of combustion of a solid propellant in a jet motor is considered. A model of unsteady combustion in motors with channel charges is proposed. The model takes into account the change in the temperature distribu-tion in combustion products induced by the change in the gas pressure (Mache effect). The unsteady gas-release rate and the temperature of combustion products are deter-mined on the basis of the Zel’dovich phenomenological approach, taking into account the change in the propellant-surface temperature (Novozhilov model) and the flame temperature (Gostintsev-Sukhanov model). The dependence of the stability limit of the solid rocket motor (SRM) on the charge-channel length and pre-nozzle volume of the motor chamber is determined. It is shown that the Mache effect leads to a signifi-cant constriction (by a factor of 1.5 to 2) of the range of stable combustion parameters in the SRM. It is found that an SRM with a channel charge has a narrower range of stability in terms of the Zel’dovich parameter k than an SRM with a butt-end charge and an identical combustion-chamber volume. For channel charges, the stability limit depends mainly on the volume of the pre-nozzle part of the combustion chamber.
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