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The objective of the present study is to analyse the transient flow through the vacuum ejector system with the help of a computational fluid dynamics method. An attempt is made to investigate the interesting and conflicting phenomenon of the continuous entrainment into the primary stream with limited mass supply from the secondary chamber. The results obtained show that the one and only condition in which a continuous mass entrainment can be possible in such types of ejectors is the generation of a recirculation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium of pressure at the onset of the recirculation zone. A steady flow assumption in such ejector systems is valid only after the dynamic equilibrium state.

The aerodynamics of projectiles launched from barrels of various devices is quite complicated due to their interactions with the unsteady flowfield around them, A compntational study using a moving grid method is performed here to analyze various fluid dynamic phenomena in the near field of a gun, such as the projectile-shock wave interactions and interactions between the flow structures and the aerodynamic characteristics ofthe projectile when it passes throngh various flow interfaces. Cylindrical and conical projectiles have been employed to study such interactions and the fluid dynamics of the flowflelds. The aerodynamic characteristics of the projectile are hardly affected by the projectile configuration dnring the process of the projectile overtaking the primary blast wave for small Mach numbers. However, it is noticed that the projectile configurations do affect the unsteady flow structures before overtaking and hence, the unsteady drag coeflicient for the conical projectile shows considerable variation from that of the cylindrical projectile. The projectile aerodynamic characteristics during the interaction with the secondary shock wave are also analyzed in detail. It is observed that the change in the characteristics of the secondary shock wave during the interaction is fundamentally diflerent for different projectile configurations. Both inviscid and viscous simulations were carried out to study the projectile aerodynamics and the fluid dynamics. Although the effect of the viscosity on the projectile aerodynamic characteristics is not significant, the viscosity greatly affects the unsteady flow structures around the projectile. NomenclatureSubscripts P S projected frontal area of the projectiles speed of sound, m/s coeflicient of drag drag force, N Mach number projectile Mach number relative to still air projectile Mach number relative to flow behind the moving shock wave shock wave Mach number at the launch tube exit. assumed parameter pressure, N/mt ime, ms velocity, m/s density, kg/mr atio of specific heats projectile shock wave = downstream and upstream of the moving shock wave

The ballistic range has long been employed in a variety of engineering fields such as high-velocity impact engineering, projectile aerodynamics, and aeroballistics, since it can create an extremely high-pressure state in a very short time. Of many different types of ballistic ranges developed to date, a two-stage light-gas gun is being employed most extensively. Since the operation of the ballistic range involves many complicated gas dynamic processes, optimization of various design parameters of the ballistic range is important for the durability of its components. In the present study, a theoretical analysis has been carried out to investigate various unsteady processes involved in the operation of the ballistic range and to assess the performance of the ballistic range. The results obtained are validated with the available experimental data. A shock tube is added in between the pump tube and launch tube and its effect on the performance of the ballistic range is quantified using the present theoretical analysis. Several methods are employed to define the ballistic efficiency. The effect of ratio of pump tube area to launch tube area on the performance is also investigated. A significant performance enhancement is obtained in the ballistic range with the addition of a shock tube.

A computational fluid dynamics (CFD) method has been applied to simulate unsteady near-field aerodynamics of the projectile which is launched from a ballistic range. A moving coordinate scheme for a multi-domain technique was employed to investigate the unsteady flow with moving boundary. The coordinate system fixed to each moving domain was applied to the multi-domains, and the effect of virtual mass was added in the governing equations for each domain. The unsteady, axi-symmetric Euler equation systems were numerically solved using the third-order Chakravarthy-Osher total variation diminishing scheme, with Monotone Upstream-centered Scheme for Conservation Laws (MUSCL) approach. The present computations were validated with results of some other CFD works and experimental data available. The computed results reasonably capture the major flow features, such as shock waves, blast waves, shear layers, vortical flows, etc which are generated in launching a projectile up to a supersonic speed. The projectile mass, configuration, and the initial conditions behind the projectile have been varied to investigate its effect on the flow field and the unsteady projectile aerodynamics. The unsteady aerodynamics of the projectile is strongly affected by the projectile mass and configuration. The initial conditions behind the projectile have strong influence on the near flow field structures which govern the development of the blast wave along with the projectile motion.