NATIONAL ADVISORY COMMITTEE FOR AEROmAvllICS PRELIMINMY INVESTIGATION OF PEKFORMANCE OF VARLAXE-TKROAT EXTENDED-PLUG-TPE N0ZZL;ES OVER WIDE RANGE

As part of an over-all program f o r the experimental investigation c of large-scale Jet nozzles, a preliminary evaluation of the internal performance characteristics of several vmiable-throat extended-plug-type nozzles uaa obtained over a range of nozzle pressure ratios from * 1.5 to 15 with nozzle throat-mea variations as great as 2:l. An extended-plug nozzle attained peak thrust coefficients as high &s those which have been attained FJlth fixed-geometry convergent-divergent nozzles. The t h r u s t coefficients of the extended-plug nozzles were relatively insensitive to both nozzle pressure r a t i o and throat area over the range investigated. The lack of sensi t ivi ty of thrust coefficient t o nozzle pressure r a t i o and throat area was evidenced primarily by the absence of. severe decreases i n thrust coefficient a t low nozzle pressure ratios which are narmally observed fo r canvergent-divergent nozzles because of overexpansion. For choked flow, the flow coefficients of the extended-plug nozzles varied from 0.95 t o 0.997. A ra t io of the outer-shell exit area to nozzle throat area was found t o be an important variable affecting nozzle performance. %st of the configurations reported herein showed a small decrease in thrust coefficient at low nozzle pressure ratlos; however, it-is believed that this characteristic can be nearly eliminated by proper nozzle design