Investigation of Exhaust Backflow From a Simulated Cluster of Three Wide-Spaced Rocket Nozzles in a Near-Space Environment
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CENTER
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A limited experimental investigation has been conducted to confirm the existence of exhaust backflow from a cluster of three widely spaced nozzles operating in a near-space environment and to determine pressure and heat- transfer coefficients in the region washed by the backflow. Experiments were conducted in a 61-foot-diameter vacuum sphere using a sine solid-propellant rocket motor and a reflection plate. The reflection plate was used to simulate the interference planes that would normally exist for a cluster of three nozzles. Data were obtained for nozzle spacings of 8.02 and 17.05 nozzle exit diameters for pressures which simulated a nominal altitude range of 3.2 x 109exp 5 to 1.8 x 10exp 5 feet. The pressure data indicated that the backflow was super- sonic for several nozzle exit diameters ahead upstream of the nozzle exit plane and that the flow over small-diameter thermocouples in this region was in the free-molecule region. Average heat-transfer coefficients obtained for small-diameter cylinders thermocouples in this region were on the order of 1 x 10exp -4 Btusq ft-sec-degrees R.