| Fin-slot solid propellant grains have been used in a variety of solid rocket propulsion systems, most notably in the Space Shuttle Reusable Solid Rocket Motor (RSRM) Boosters. Advantages that can arise from using fin-slot grains compared to conventional end-burning or center-perforated grains include a relatively constant burning surface area and thrust level, large free volume, and greater exposed surface area for reliable ignition. The influence of the igniter jet can have a profound effect on recirculating flow patterns, due to impingement angle, degree of under-expansion, and strength of the induced vortex. In order to accurately predict the overall RSRM ignition transient, it is necessary to have knowledge of the igniter induced flow, heat-transfer, and flame-spreading rates inside the fin region. This research was aimed at obtaining a better understanding of the effect of flame spreading in the fin-slot section of the rocket motor.;Experimentally, a subscale (roughly 1:10) pie-shaped fin-slot motor was designed to simulate two fin-slot regions. The test rig consisted of a head-end igniter, a fin-slot propellant section, a downstream cylindrical propellant grain section, and an interchangeable external exit nozzle. Diagnostically, the motor was equipped with pressure transducers, a set of sacrificial and main viewing windows for real-time imaging, and a diagnostic holder capable of mounting an array of flush-mounted heat-flux gauges, near-IR fast-response photodetectors, acoustic emission sensors, or fine-wire thermocouples in a perpendicular orientation.;The first part of this study dealt with the design and assembly of the rocket motor along with the testing and analysis of the igniter induced flow field and heat-transfer to the propellant surface. Experiments were conducted using heated air flow as well as the direct discharge of a live igniter onto an inert fin-slot propellant sample. Results were used to develop a heat-transfer correlation within the fin-slot region. Deduced heat-transfer rates from this correlation were in good agreement with the measured data within experimental error.;The second part of this study was the observation and characterization of the flame-spreading phenomena across the fin-slot surface using a combination of a high-speed digital camera and non-intrusive photodetector optical methods. A dimensionless flame-spreading interval correlation was developed. The flame-spreading interval was found to be inversely proportional to the local fin-slot pressurization rate to the power of 0.62. Therefore, the greater the pressurization rate, the shorter flame-spreading interval. |
