IN addition to providing a propulsive force to a flying vehicle or a rocket

IN addition to providing a propulsive force to a flying vehicle or a rocket, a rocket propulsion system can also provide certain control mechanisms to change vehicle’s attitude and trajectory via thrust vector control (TVC) systems. By controlling the direction of the thrust vector pitching, yawing and rolling moments can be achieved on the flying body, specifically there are many ways to deflect the thrust vector such as using gimbaled nozzles, flexible nozzle joints, jet vanes/tabs, jetavators, secondary injectants, and etc. Among different techniques to generate deflection of thrust vector of a rocket system, Secondary Injection Thrust Vector Control (SITVC, a shock producing TVC technique) has been used in various systems successfully since 1960’s and is accomplished by injecting a secondary fluid inside the supersonic flow from the diverging part of the converging-diverging nozzles. On contrary to mechanically operating TVC systems, such as gimbaled nozzles, jet vanes/tabs, etc., which require actuators to deflect mechanical parts, SITVC does not require any moving parts and regulated by the fluid injection, which reduces axial thrust force losses while changing the direction of the vector 1 The secondary fluid injected, (gas or liquid) can be supplied from a separate gas generator or from the combustion chamber as bleed and it creates a complex flow field inside the nozzle. This complex flow field contains not only a strong bow shock creating asymmetry and a weak separation shock due to boundary layer separation upstream of the injector but also a Mach disk and reattachment region accompanied by recompression downstream of the injection location 2-4. Figure1. 2 Schematically depicts the flowfield structure inside the nozzle setup as a result of secondary injection. The causes of the deflection or more appropriately the side force to create deflection. The net side thrust produced is a combined effect of a) jet reaction force, caused by the momentum of the secondary fluid (injectant), and b) interaction (induced) force, due to pressure rise along the wall 5. Since the interaction of secondary jet with the main flow is quite complex earlier studies focused on both theoretical tools such as Blast-wave analogy4 to model the penetration of the secondary jet into main flow and experiments with cold flow tests6,7 and also real firing tests8,9. However theoretical models deals only with very low injection flow rates and lack generality but both cold flow tests and static firing tests gives the main SITVC data to be used for further analyses although they only provide macroscopic performance estimations and are expensive. On the other hand Computational Fluid Dynamics (CFD) has been developed to examine detailed microscopic description of fluid flows becoming a strong alternative to previous theoretical models and a complimentary element to experiments 10, 11.