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The propulsion system not only provides a propulsive force to a rocket or any flying vehicle but also can introduce a control mechanism to change the trajectory and vehicle’s attitude by thrust vector control (TVC) systems. With the control of thrust vector direction, pitching, yawing and rolling moments can be accomplished on the flying vehicle, there are many techniques that generates the deflection of the thrust vector such as using gimbaled nozzles, flexible nozzle joints, jetavators, jet vanes/tabs, secondary injectants, and etc. Among the different ways to deflect thrust vector of a flying vehicle, Secondary Injection Thrust Vector Control (SITVC, a shock producing TVC technique) has been used successfully in different systems since 1960’s and is achieved by injecting a secondary fluid inside the supersonic flow of the diverging part of the converging-diverging nozzles. On contrary to mechanical thrust vector control systems, such as gimbaled nozzles, jet vanes/tabs, jetavators etc., that uses an actuation system to move the mechanical parts, SITVC does not use any movable parts and is governed by flow regulation, which minimize the losses of the axial thrust force during changing the thrust direction 1 The secondary fluid injected, (gas or liquid) can be supplied from the combustion chamber as a bleed or from a separate gas generator and it creates a complex flow field in the nozzle divergent part. This complex flow field contains many features in addition to the strong bow shock that creates asymmetry and a weak separation shock due to separation of the boundary layer upstream of the injection location, there are also downstream of the injector a Mach disk and reattachment region accompanied by recompression were created 2-4. Figure1. 2 Schematically depicts the flow field structure inside the nozzle setup as a result of secondary injection. The causes of the deflection are as a result of the side force which produced by a combined effect of, a) interaction (induced) force, due to pressure rise along the wall, and b) jet reaction force, caused by the momentum of the secondary fluid (injectant) 5. As the secondary injection in the supersonic flow creates a complex flow field, many past researches focused on both theoretical tools such as Blast-wave analogy4 to characterize the flow field due to secondary injection and experiments with cold flow tests6,7 and static firing tests8,9.While theoretical models deals only with very low injection flow rates and lack in general, the experimental tests of cold flow and static firing provides the main data of SITVC to be utilized for further analyses, but these tests gives only macroscopic performance predictions with high cost. On the other side evolution of the computational power and numerical methods, results in developing the computational Fluid Dynamics (CFD) to give a detailed microscopic description of fluid flows which became an accurate alternative to theoretical models and a complimentary element to experimental tests 10, 11.

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