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Unsteady One-Dimensional Flow
Published in George Emanuel, Analytical Fluid Dynamics, 2017
Ballistics can be subdivided into internal, intermediate, external, and terminal regimes. For internal ballistics, the bullet or projectile is inside the gun barrel. In the intermediate regime (Merlen and Dyment, 1991; Jiang et al., 1998), the projectile is near the muzzle and the gas dynamics of the fow feld caused by the gas discharge from the barrel are of primary interest. External ballistics deals with the projectile in free fight, while terminal ballistics involves the interaction with a target. A gas dynamically oriented introduction to internal ballistics is provided in this section. Other resentations, which include additional references, can be found in the book by Farrar and Leeming (1983) and in the articles by Krier and Adams (1979) and by Freedman (1988). Our objective is to illustrate how unsteady waves can be utilized to understand the dynamics involved in internal ballistics. To avoid undue length and complexity, a number of assumptions and approximations are introduced. Suffcient physical content, however, is retained in order that the presentation should still be representative of the actual situation.
Response surface analysis of nozzle parameters at supersonic flow through microjets
Published in Australian Journal of Mechanical Engineering, 2023
Turki Al-Khalifah, Abdul Aabid, Sher Afghan Khan, Muhammad Hanafi Bin Azami, Muneer Baig
The sudden expansion in high-speed aerodynamics flows plays a significant role in dealing with external ballistics in supersonic aerospace vehicles and aerospace engineering applications. The sudden growth in the area results in two zones: the main and the other in the wake region. In an abrupt expansion after partition, the flow gets attached to the duct wall, and later towards the trailing edge again, the shear layer is formed (Figure 1). The pressure in the wake area is usually sub-atmospheric. It is found that the drag force due to the flow separation contributes significantly, and it may be around two-thirds of the aerodynamic vehicles’ overall drag force while scanning the literature. It is found that because of the presence of the positive pressure ratio, which generally occurs wherever there is a sudden expansion flow field, a flow reversal may occur downstream due to the growth of the boundary layer. Due to the positive pressure gradient, the base pressure may be increased by this reverse flow. This reverse flow will interfere with the vortex in the wake area, and the reverse flow will disturb the vortex. This phenomenon will result in an additional mass being expelled from the base region and redirected into the main flow.
An uncertain optimization method for overall ballistics based on stochastic programming and a neural network surrogate model
Published in Engineering Optimization, 2019
Liqun Wang, Guolai Yang, Qinqin Sun, Jianli Ge
The overall ballistic process is a multidisciplinary problem. Numerous studies have been conducted on a single ballistic process; however, even for a similar ballistic problem, different research groups have proposed different models and methods according to their research area. Research on interior ballistics has evolved from the classical internal ballistic model (Woodley 2001) based on thermodynamics and Lagrange's assumption to the two-phase flow interior ballistic. For example, Gollan and Jacobs (2013) described the formulation of the gas dynamics and high-temperature thermochemical modules of the Eilmer code. Luo and Zhang (2015) used a one-dimensional two-phase reaction flow model and MacCormack difference scheme to simulate the launch process of a multiple-projectile system. In theoretical studies of the projectile initial disturbance, Soifer and Becker (1983, 1984) established the differential equations of the projectile motion in a flexible gun tube. Later, the projectile swing equations in the semi-restricted period as well as the after-effect period were also proposed (Kang, Wu, and Ma 1999). In recent years, software simulations of the projectile motion have flourished. Chen (2010) studied the effect of axis bending on the projectile movement using ABAQUS. Li et al. (2016) established the projectile–gun coupling launch dynamic model. In their studies, results of the rotating band deformation, the projectile motions and the dynamic engraving resistance were obtained. In the external ballistics field, the exterior ballistic equations have been widely used to calculate the shooting parameters. The combination of external ballistics and Monte Carlo simulation has been widely used to calculate the firing dispersion. In addition, researchers are continually adopting new computational models and methods to modify the semi-empirical formulae for projectile aerodynamic characteristics (Massey et al.2008; Pierre 2007).