Ultrasonic measurements of solid propellant burning rates in nozzleless rocket motors

Abstract

Burning rates at several axial locations along the grain port of subscale nozzleless motors were measured by ultrasonic transducers that detect the instantaneous web thickness of the propellant. Two experimental devices were used for this: an axisymmetric nozzleless motor loaded with a metallized composite propellant and a twodimensional window nozzleless setup loaded with a nonmetallized composite propellant. The ultrasonic transducers give an estimate of the grain deflection during motor pressurization. In both setups, the nocrossflow burning rate measured in the head-end region agrees with standard strand burner data, and high erosive burning rates are found in the aft-end region. These erosive burning data have been represented in a format that includes the main experimental variables: port radius or channel width, no-crossflow burning rate, and mean crossflow velocity. The results reveal that the generally observed trends of threshold specific mass flow rate, no-crossflow burning rate sensitivity, and scale dependence are also demonstrated in nozzleless motors.