Performance of the aerobell extendible rocket nozzle

Extendible nozzles are currently being considered for space propulsion. The aerobell is one promising configuration for this application. The nozzle extension is a translating shroud cooled by the engine turbine exhaust gases. The turbine exhaust is introduced subsonically into a step discontinuity at the basic nozzle extension interface and separates the primary stream and the extension walls. Results of an extensive theoretical and experimental program for the design and performance analysis of aerobell engines are discussed. The theory is compared with data taken from cold-flow and simulated hot-flow test results. The results indicate that the aerobell provides performance gains on the order of 2% relative to the basic nozzle. The performance trends and magnitudes are shown to be predictable (within 0.3%) using the methods developed. Nomenclature A = area Cp = nozzle thrust coefficients, F/PCA * c* = characteristic velocity, PcA*gc/w D = diameter F = thrust gc — gravitational units conversion factor L = nozzle axial length P = pressure R = radius T = temperature w = flow rate, Ibm/sec