Typical Projectile Research Articles

Heat flux characteristics within and outside a forward facing cavity in a hypersonic flow

A forward facing cavity effect on heat flux variations inside the cavity and over the nose surface is studied over a typical projectile geometry using the shock tunnel experiments. The flow oscillation will tend to oscillate the shock, which in turn varies the heat flux over the nose surface as well as inside the cavity. The higher length to diameter (L/D) ratio of the cavity plays an important role in nose surface heat flux reduction and investigated for L/D = 1, 2 and 3 by a uniquely designed model. The cavity flow oscillation period is determined, using the base pressure and surface heat transfer signals measured inside the cavity with reference to the pitot probe steady test time and shock oscillation period. The frequency analysis for oscillations is performed using the fast Fourier transformation. Experimental results showed that, the mean nose surface heat flux reduced by ≈4.6% to ≈7%, ≈6% to ≈8% and 3% to ≈31.4 and the mean shock standoff distance (l) is increased by ≈13%, ≈25% and ≈35% for L/D = 1, 2 and 3 configurations respectively with reference to the baseline geometry (without cavity geometry). As L/D increases, the nose surface location on which the heat flux reduction is observed moves towards the cavity lip and more surface area is covered with lower heat flux. Cavity region heat flux variations are studied by incorporating the thin film sensors over the cavity surface and it is observed that, a significant ≈32.5% to ≈36%, and ≈28% to ≈58% lower mean heat flux for L/D = 2 and 3 respectively with reference to the baseline geometry stagnation point heat flux.

Study of Flying Projectile’s Properties of Infrared Radiation

In order to solve the problem that the optic-electric detecting target board fails to work at nights or under low light level，it has studied the flying projectile’s properties of infrared radiation and the radiation attenuation properties of the flying projectile in the atmosphere. Through establishing the differential equations, the projectile’s surface temperature is obtained to calculate the flying projectile’s infrared radiation properties , according to atmosphere’s transmitting properties，the calculation method of atmospheric transmittance rate. The infrared radiation properties of three typical projectile are simulated by utilizing MATAB. The simulation result shows that the surface temperature of the flying projectile has a linear change with its velocity; the atmospheric transmittance rate is inversely proportional to the detection distance; Once the atmospheric attenuation factor is different, then the radiation energy received by the detector will be different.

Cratering experiments on the self armoring of coarse-grained granular targets

Recently published crater statistics on the small Asteroids 25143 Itokawa and 433 Eros show a significant depletion of craters below approx. 100m in diameter. Possible mechanisms that were brought up to explain this lack of craters were seismic crater erasure and self armoring of a coarse, boulder covered asteroid surface. While seismic shaking has been studied in this context, the concept of armoring lacks a deeper inspection and an experimental ground truth. We therefore present cratering experiments of glass bead projectiles impacting into granular glass bead targets, where the grain sizes of projectile and target are in a similar range. The impact velocities are in the range of 200–300ms−1. We find that craters become fainter and irregular shaped as soon as the target grains are larger than the projectile sizes and that granular craters rarely form when the size ratio between projectile and target grain is around 1:10 or smaller. In that case, we observe a formation of a strength determined crater in the first struck target grain instead. We present a simple model based on the transfer of momentum from the projectile to this first target grain, which is capable to explain our results with only a single free parameter, which is moreover well determined by previous experiments. Based on estimates of typical projectile size and boulder size on Itokawa and Eros, given that our results are representative also for kms−1 impact velocities, armoring should play an important role for their evolution.

Modeling and reduction of shocks on electronic components within a projectile

Electronic components within a projectile are subjected to severe loads over an extremely short duration during the launch process. Failure of these components during launch can result in negative effects on the mission of the projectile. While experimental data can be helpful in understanding failure of electronic components within a projectile, collecting such data are usually difficult. There are also limitations on the reliability of sensors under these circumstances. Finite element modeling (FEM) can offer a means to better understand the behavior of these components. It can also be used to develop better shock mitigation features into the projectile design. This research has two objectives. The first objective is to develop an FEM that one describes the interaction of a typical projectile with the gun barrel during launch. The projectile includes a payload of a one-pound mass representing a typical electronic package supported by a plate. The second objective of this work is to investigate the use of composite plates to support electronic payload as a means to reduce the transmitted shocks during the projectile launch event. The proposed plate has carbon fibers embedded in an epoxy matrix. A parametric study of the effects of varying the thickness of the supporting plate and the fiber volume fraction on the accelerations and stresses is included. Results of the study are used to reach general recommendations regarding reducing failure of electronic components within a projectile.

Premature in‐bore separation of sabot‐jacketed projectiles

AbstractThe premature separation of saboted projectiles undergoing high‐mach‐number in‐bore acceleration is investigated. Results from a simplified numerical model for the problem are presented. Measured short‐term velocity history for a typical projectile is used to describe the motion of a nonuniformly accelerating piston. Two numerical algorithms for calculating the shocked flow in tront of the accelerating piston are presented. Mach number and pressure time histories for the flow afford corrective input to the sabot design process. © 1993 John Wiley & Sons, Inc.

Study of Trajectory of Spin-Stabilised Artillery Projectiles

Equations of motion for conventional spin-stabilised artillery projectile have been derived using a pseudo-stability axes system in addition to body-fixed and space-fixed axes systems. The aerodynamic forces and moments have been represented by their respective coefficients and the effects of Mach number and Reynolds number have been suitably accounted. The magnus terms which are significant at high rates of spin are estimated using a simple model. The set of equations have been partly linearised and solved numerically for a typical projectile using NAG system routines. Various trajectory parameters are computed and compared with the range-table data for the projectile. A parametric study had been carried out varying the aerodynamic coefficients to understand the sensitivity of the results obtained.

Finite compressibility in shaped charge jet and long rod penetration—the effect of shocks

The classical theory of high speed jet and long rod penetration assumes incompressibility of both projectile and target. We extend here previous analyses of the implications of finite compressibility by including the effect of stationary shocks. For uniform projectile velocities V≲6×103 ms−1, depending on the type of target material, the total effect of compressibility is in the order of 10% or less, and is well approximated by the volume compressison work considered in the previous analyses [A. Coombs, private communication, Royal Air Force Research and Development Establishment, 1978; B. S. Haugstad, J. Appl. Phys. 52, 1243 (1981)]. At higher velocities shocks play an increasingly dominant role, contributing at least equally to the total compressibility effect at V≲104 ms−1. At these velocities there is a reduction in penetration depth of 10–20% in targets of aluminium or lead, while for plexiglass a full 35% reduction is predicted. Targets of lead or plexiglass experience local melting or even sublimation during penetration. In targets of aluminium, steel, platinum, and probably also in most other metallic targets, melting or sublimation first occurs well above typical projectile velocities.