Altitude Adjustable Rocket Nozzles Using Passive Flow Control

The backward facing steps nozzle (BFSN) is a new developed flow adjustable exit area nozzle for large rocket engines. It consists of two parts, the first is a base nozzle with small area ratio and the second part is a nozzle extension with surface consists of backward facing steps. The number of steps and their heights are carefully chosen to produce controlled flow separation at steps edges that adjust the nozzle exit area at all altitudes (pressure ratios). The BFSN performance parameters are assessed numerically in terms of thrust and side loads against the dual-bell nozzle (DBN) with the same pressure ratios and cross sectional areas.The results show that the flow separation location is axi-symmetric inside the BFSN with symmetrical pressure distributions over the nozzle circumference at different pressure ratios. While the DBN results show an asymmetrical flow separation locations over the nozzle circumference at all pressure ratios. The results show that the side loads in the BFSN is 0.01%-0.6% of its value in the DBN for same pressure ratio.