Three dimensional numerical investigation of the clustered linear aerospike nozzle’s flow affected by changing the distance between neighboring cell nozzles

Aerodynamic performance of the simplified test models of infinite consequence clustered linear aerospike nozzles was numerically investigated and results were compared with those of an experimental study. The model of numerical target is focused on predicting the ramp pressure distribution and the effect of interval of the neighboring clustered cell nozzles, where jet exhaust flow emits 3.5 in Mach number. Its thrust performances were examined in terms of two types of the cell nozzle interval, 4 and 17 mm, whose model is named half4c and half3c respectively. Clustered cell nozzles connect with a straight ramp, and another end of the straight ramp connects with a 12-degree-inclined slope ramp. The ramp consists of a pair of these ramps. External main flow in Mach 2.0 impinges on the N₂ cell nozzle jets and ramp surface. On the ramp surface, pressure distribution illustrated clear cell pattern resulting from three-dimensional bumpy oblique shock wave generated above slope ramp. NDP (Normalized Difference Pressure) at ramp of CFD was compared with that of experiment. It showed quantitative agreement within 10% difference. NDP distribution at jet center of span wise cross-section showed opposite phase differences from that at base center. Flow features from streamline showed the presence of vertical vortex and the deflection of main flow and jet flow. Streamline not only showed how to mix between these flows but also suggested that oblique shock wave generated at front half of a slope ramp was bumpy as shown in the great deflection of stream. At half4c model, main flow did not sink to near the ramp wall except in the case of over-expansion, while at half3c model a part of main flow was mixed with jet flow at jet center only in the case of over-expansion. Thus flow features could be classified by whether expansion form is over-expansion in both cell nozzle intervals. The ramp pressure distribution reflects to pressure thrust. Consider the situation that straight ramp angle against the virtual airframe axis plane can be changed. At this time, the airframe angle of making thrust maximum tended to decrease with increase in NPR and with becoming shorter in cell nozzle interval.