Flowfield structure in a fin-slot solid rocket motor (Part I)

To accurately predict the overall ignition transient for the reusable solid rocket motor of the space shuttle booster with head-end fin slots, it is necessary to acquire detailed flowfield structure and energy transfer rates on the exposed inert fin-slot propellant surfaces. This paper is the first of a two-part study and deals with the internal flowfield structure and heat-transfer characteristics in the fin-slot region. A subscale (1:10) pie-shaped fin-slot motor was designed to perform diagnostic measurements. An array of 36 flush-mounted heat-flux gauges was installed to detect the local temperature-rise rates at representative regions perpendicular to the propellant surface. Flowfield visualizations were conducted by applying either a chalk-powder/kerosene mixture or many small threads taped to various locations on the inner surface of the sacrificial window of the fin-slot region for high-speed video camera recording. Computational fluid dynamics simulations were performed for modeling the internal flowfield of the test rig. Results were used to develop a heat-transfer correlation governed by the internal flowfield structure within the fin-slot region. The theoretically calculated and experimentally observed internal flowfield patterns were similar in nature. The heat-transfer rates determined from the developed correlation matched the measured data trend within the experimental error. The flowfield structure and heat-transfer rate distribution are mainly governed by the major recirculating flow induced by the igniter jet.