Stability Prediction for Solid Propellant Rocket Motors with High Speed Mean Flow.
AIR FORCE ROCKET PROPULSION LAB EDWARDS AFB CA
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Current stability prediction calculations for solid propellant rocket motors are based upon a simple first-order perturbation solution which assumes an incompressible chamber mean flow. Since combustion instability is frequently observed in motors with large length-to-diameter and low port-to-throat area ratios, there is concern that the standard stability techniques should be extended to apply to cases where high-speed mean flows are present. This report shows how the basic stability analysis can be extended by carrying additional terms in the perturbation expansions. Compressibility affects the calculations in several ways. The acoustic mode shapes predicted in the linear model are distorted and the mean thermodynamic properties may vary significantly from point to point in the chamber. These variations and distortions alter both the predicted growth rates and also the frequencies for the acoustic modes. Detailed calculations are carried out for a cylindrical grain geometry with longitudinal wave motions. Frequency and growth rate corrections grow quadratically with increases in the port length-to-diameter ratio. Frequency shifts of as much as 30 percent of the linear acoustic frequency predictions may be expected in high LD motors. Author
- Numerical Mathematics
- Combustion and Ignition
- Solid Propellant Rocket Engines