Cold-flow tests and analysis of linear clustered plug nozzles with six round-to-square inner nozzles

Air cold-flow tests on the linear clustered plug nozzles with six round-to-square inner nozzles were carried out to investigate the altitude compensation characteristic and effects of gap between modules and plug sidewall on the nozzle performance. The plug flow fields at sea level, middle altitude and high altitude are presented using schlieren technique. Combining the plug surface pressure profiles by numerical computation with the experimental data, effects of gap between modules and plug sidewall on the nozzle performance are also studied. The test results show that the plug nozzle models are capable of altitude compensation and the thrust coefficient efficiency of the best model is in the range of 0.90-0.95 from low to high altitude. The nozzle efficiency at design altitude is about 0.95, which is under the theoretic prospective. The performance loss is caused by the round-to-square inner nozzle contour, the plug truncation, multi-module effect, the opened plug base, etc.