Performance aspects of plug cluster nozzles

Plug and plug cluster nozzles are said to have superior performance compared to that of conventional nozzles, A preliminary comparison of different nozzles at an identical area ratio shows that at the nozzle design point the plug cluster nozzle performs slightly worse than a conventional or an extendible bell nozzle. However, for certain applications, such as atmospheric flight or the realization of high area ratios at short nozzle lengths, advantages of the plug cluster nozzle may exist. Any plug-cluster-nozzle performance model must include the effects of the merging stream tubes emanating at the module exists as well as a reliable determination of the pressure acting on the base area of the truncated plug. The fundamental performance elements of a general plug-cluster-nozzle performance model are discussed, and, as far as already elaborated, solutions are presented. A theory for base pressures of truncated cylinders is adapted to plug nozzles and shows good agreement with the few available cold-flow test data.