Breech Pressure Research Articles

Embracing Anisotropy – Opportunities and Challenges to the Functional Application of Advanced Manufacturing of Energetic Materials

Embracing Anisotropy – Opportunities and Challenges to the Functional Application of Advanced Manufacturing of Energetic Materials

Pressure Response Optimization of an Eddy Current-Driven Flyer Plate Valve for the ITER Shattered Pellet Injection System

One technique for mitigating disruptions in a tokamak is shattered pellet injection (SPI). SPI is a process in which a large solid pellet consisting of deuterium, neon, or argon is desublimated in a pipe gun barsrel and launched downstream. Pellets are shattered just before entering the plasma by an impact with an angled tube. Injection of these materials into the plasma radiates stored thermal energy, limits current decay rates, suppresses the generation of runaway electrons, and dissipates runaway electrons if necessary. A critical element of the SPI system is a fast-acting valve that releases high-pressure gas to dislodge and accelerate pellets directly, or indirectly via a mechanical punch. A prototype valve sized for the ITER SPI system has been designed and fabricated. A pulsed high-voltage power supply energizes the valve’s internal magnetic coil, which induces eddy currents in the adjacent flyer plate resulting in a repulsive force between the flyer plate and the coil. The flyer plate action lifts a valve seat, allowing high-pressure gas to flow from the valve plenum to the downstream (breech) location of the pellet or mechanical punch. All of the valve’s internal components are designed to operate in ITER-level static background magnetic fields. A study was conducted to optimize the downstream pressure response for a range of valve sizes and operating pressures. In particular, the study analyzes the breech pressure response associated with varying plenum pressures as well as varying breech volumes. A computational fluid dynamics simulation was built in STAR-CCM+ and validated against data from laboratory experiments. The resulting simulation outputs, in the form of downstream responses for a variety of initial plenum pressures and breech volumes, will be used as a complement to experimental data to ensure the pressure pulse is suitable for pellet survivability. These data, combined with studies on pellet shear strength and shock response, will be applied to optimization of overall operating parameters of the ITER SPI system.

A calculation method of interior ballistic two-phase flow considering the recoil of gun barrel

The theory of interior ballistic two-phase flow (IBTPF) is the primary means to study the distributions of physical quantities in gun chamber. In previous calculations, the gun breech is usually simplified as a fixed wall boundary, totally ignoring the effect of gun barrel recoil on interior ballistic processes. Thus to truly describe the interior ballistic process of the self-propelled gun (SPG), the transfer matrix method of multibody system (MSTMM) is combined with the theory of IBTPF in this paper. By simultaneously solving the generalized coordinate equations of multibody system and the conservation equations of IBTPF, the gun barrel recoil is converted to the moving boundary of the gun breech, and a more accurate calculation method of IBTPF is established. The results show that the simulated vibration characteristics, dynamic response during launch as well as interior ballistic performance of the SPG are all in good agreement with test values. Compared with no recoil, the gun barrel motion affects the growth regularity of the chamber volume behind the projectile, and eventually results in the changes of interior ballistic performance indexes such as maximum breech pressure and muzzle velocity. Overall, this study provides a more accurate prediction and simulation tool to enable better insight into such complicated interior ballistic processes, which is of great significance to the launch safety analysis and subsequent ballistic calculations.

Experimental and Finite Element Studies on Man-Rifle Reaction Force

The study concerns a man-weapon interaction during a gunshot. The recoil force measurements obtained for the Kalashnikov automatic rifle are presented and analyzed. The influence of shooter’s mass, height and position is described. The breech pressure and projectile velocity data are presented as well. In addition, a finite element (FE) model of the shooter-rifle system is developed in order to qualitatively assess the quantities which could not be determined experimentally, i.e. the stress, strain and displacement fields which are generated in the human body due to the rifle recoil. Several conclusions are drawn that allow for better understanding of the recoil phenomenon and can be useful from the weapon designer’s point of view.

Application of transient burning rate model of solid propellant in electrothermal-chemical launch simulation

A 30mm electrothermal-chemical (ETC) gun experimental system is employed to research the burning rate characteristics of 4/7 high-nitrogen solid propellant. A modified 0D internal ballistic model is established to simulate the ETC launch. According to the measured pressure and electrical parameters, a transient burning rate law including the influence of enhanced gas generation rates (EGGR) coefficient by electric power and pressure gradient (dp/dt) is added into the model. The EGGR coefficient of 4/7 high-nitrogen solid propellant is equal to 0.005MW-1. Both simulated breech pressure and projectile muzzle velocity accord with the experimental results well. Compared with Woodley’s modified burning rate law, the breech pressure curves acquired by the transient burning rate law are more consistent with test results. Based on the parameters calculated in the model, the relationship among propellant burning rate, pressure gradient (dp/dt) and electric power are analyzed. Depending on the transient burning rate law and experimental data, the burning of solid propellant under the condition of plasma is described more accurately.

Numerical simulation of gas-solid two-phase reaction flow with multiple moving boundaries

Purpose – In engineering applications, gas-solid two-phase reaction flow with multi-moving boundaries is a common phenomenon. The launch process of multiple projectiles is a typical example. The flow of adjacent powder chambers is coupled by projectile’s motion. The purpose of this paper is to study this flow by numerical simulation. Design/methodology/approach – A one-dimensional two-phase reaction flow model and MacCormack difference scheme are implemented in a computational code, and the code is used to simulate the launch process of a system of multiple projectiles. For different launching rates and loading conditions, the simulated results of the launch process of three projectiles are obtained and discussed. Findings – At low launching rates, projectiles fired earlier in the series have little effect on the launch processes of projectiles fired later. However, at higher launching rates, the projectiles fired first have a great influence on the launch processes of projectiles fired later. As the launching rate increases, the maximum breech pressure for the later projectiles increases. Although the muzzle velocities increase initially, they reach a maximum at some launching rate, and then decrease rapidly. The muzzle velocities and maximum breech pressures of the three projectiles have an approximate linear relationship with the charge weight, propellant web size and chamber volume. Originality/value – This paper presents a prediction tool to understand the physical phenomenon of the gas-solid two-phase reaction flow with multi-moving boundaries, and can be used as a research tool for future interior ballistics studies of launch system of multiple projectiles.

1차원 수치 해석을 통한 강내탄도 성능해석

Performance analysis of the interior ballistics has been conducted using the 1-D numerical code called IBcode according to the various conditions such as length of ignition-gas injector, amount of ignition-gas, mass of projectile, and drag force of projectile. In case of the length of ignition-gas injector, the 25~100 % of the full-injector length has been considered as well as the mass & mass flow of the ignition-gas. The mass of the projectile 5~70 kg and its drag force of 0~69 MPa have been also considered. Variables such as breech & base pressure, negative differential pressure and muzzle velocity for the performance analysis have been sorted, too. Firing conditions for the optimal performance have been investigated through these variables.

Optical Characterization of Large Caliber Muzzle Blast Waves

AbstractHigh‐speed, 1,600 Hz, visible imagery of the blast wave from 147 firings of a 152 mm howitzer were observed for three different propellant charges. Blast wave trajectories were determined at 0.5–13 m from the muzzle exit, yielding initial velocities of Mach 3–4 that decayed to near acoustic within the imager field of view. A piecewise treatment of the Taylor‐Sedov point blast model was sufficient to describe the trajectories with an average error of 0.1 m. The trajectories were consistent with a three‐dimensional expansion and constant rate of energy release. A Constant Breech Pressure gun model was used to estimate total energy of the muzzle flow, and the efficiency of depositing energy into the blast wave was 18–24 %. Plume temperatures of approximately 980–1,210 K were estimated by partitioning energy and were correlated with likelihood of plume combustion. Classification of charge type based on energy deposition rate was modest, characterized by a ratio of between‐class to within‐class variance of 1.3, for the very similar events.

Aerodynamic Analysis of Projectile in Gun System Firing Process

During a gun firing, the flow around a projectile will be developing and changing. In particular, the flow around the projectile is disturbed significantly when the projectile overtakes the muzzle flow. Furthermore, the projectile body pressure will also change substantially. Therefore, the shot ejection process has an important effect on the shot accuracy. The maximum projectile velocity is one of the most important design goals of the interior ballistic process and also is the initial condition for the exterior ballistic process. Most researchers take the muzzle velocity as the maximum projectile velocity; actually, after the projectile exits the muzzle, the projectile velocity will increase further due to the influence of the muzzle flow. Most investigations of the muzzle flow focused on the blowout of the high-pressure jet flow after the projectile exited the muzzle. The interior ballistic process was ignored or simply assumed in most investigations. Also, the mutual influence between the moving projectile and the muzzle flow was often neglected. Actually, a precursor shock flow near the muzzle is formed before the projectile exits. This precursor muzzle flow has an important influence on the trajectory of the projectile, especially, for the prevalent trend of gun systems including large caliber cannon and multiple launch gun systems. For these reasons, the interior ballistic process was coupled with the simulation of the flow near the muzzle. A hybrid structured-unstructured gridding method was used to simulate the process from the projectile engraving to the gas ejection phase, accounting for the moving projectile. The simulation results show that the projectile muzzle velocity was 893.99 m/s but the maximum velocity was 899.28 m/s. The projectile velocity increased rapidly to up to 0.8 ms after muzzle exit; thereafter, the projectile velocity increased slowly before reaching its maximum value. The maximum Mach number of the effluent gas increased to 6.83 and the breech pressure decreased to 21.5 MPa at 1.8 ms after the projectile exited the muzzle. The formation and development of the muzzle flow field was highly complex and transient. The analysis of the projectile velocity was conducted during the interior ballistic after-effect period. The predicted muzzle velocity and maximum barrel pressure are in good agreement with those measured in gun firings. Results of the numerical simulation and analysis are helpful to understand and master the aerodynamic process of gun system launching and provide significant guidance for research into shot accuracy and muzzle brake design.

A special design condition to increase the performance of two-stage light-gas guns

Abstract This paper reports a theoretical and numerical study aimed at increasing the operating efficiency of two-stage light-gas guns by appropriately changing their working conditions. In particular, a method is presented for increasing the projectile speed without any rise of the maximum breech pressure. The classic design theory of two-stage guns starts from the assumption that the highest velocity is reached in a gun which constantly maintains the maximum acceptable pressure at the base of the projectile during the full launching time. The main drawback of this working condition is that it may require an unfeasible rise of the gun maximum pressure, especially when very high muzzle speed is requested. To overcome this limitation, a new reference case different from the constant-base-pressure one is presented, based on a novel gas-dynamics solution that can be expressed in exact form if losses are not accounted for. According to such an approach, it is theoretically shown that the projectile base-pressure can be appropriately shaped (i) to improve the final speed without increasing the breech pressure or, in other terms, (ii) to achieve a given muzzle velocity with reduced maximum gas pressure. The analytical application of the new gas-dynamics condition showed the capability of obtaining a 1 km/s velocity improvement with no increase of the breech pressure or, alternatively, a pressure reduction up to 30% with no penalty on the model final speed. A numerical verification of the calculations was performed through the CISAS light-gas gun full numerical model, which includes real effects such as friction losses and heat transfer. Finally, an experimental verification of the numerical test case was attempted and a speed augmentation of 0.8 km/s with no increase in the breech pressure was confirmed in laboratory, highlighting the agreement with numerical predictions.

Numerical Analysis of Projectile-Launch Tube Wall Friction Effects on Projectile Acceleration in Single-Stage Gun

The effects of the friction between the projectile and launch-tube wall in a single-stage gun are examined by the interior ballistics simulations. The solid/gas two-phase flow code for two-dimensional axisymmetric calculation is used in the simulations. In this study, one-dimensional quasi-steady-state elastic relations are applied to the projectile in the estimation of the friction force. The calculation method is validated by the comparison of the simulated results with the experimental data such as the histories of the breech pressure and the projectile acceleration. The simulated results reveal that the impact of the shock waves to the base increases the friction force acting on the projectile. The large friction force in the tight fit case decelerates the projectile, consequently intensifying the chamber pressure. The muzzle velocity decreases with the increase of the projectile diameter, and this appears strongly in the low chamber pressure case.

Experimental Ballistic Improvement in a Pure Electrothermal (ET) 25-mm Gun

The Soreq Propulsion Physics Division has recently initiated the development of a small-caliber pure electrothermal (ET) weapon. This paper reports the promising results obtained with a 25-mm ET gun. The currently mature gun technology based on conventional ballistic process is mostly limited because: 1) the propellant burning features dictate a curve that is entirely determined by the grain geometry and cannot be changed "online" and 2) the pressure gradient between the breech and the projectile's base strongly depends on the molecular weight of the combustion gases, which is almost propellant formulation independent. Removing the first limitation and reducing the second one is the key of the ET technology. ET guns use electric energy as the unique source of propelling energy. It is converted into a high-temperature plasma which interacts in the chamber with an inert cooling fluid that serves also as a propelling working fluid. In this study, two types of working fluids were tested: polyethylene and water. Polyethylene was found unsuitable for our purposes. Experiments, supported by simulations, show that the degree of water dissociation was enough to produce the required working fluid. Using 750 kJ of ET energy, 20% improvement in kinetic energy was obtained with a standard projectile without exceeding the maximum authorized breech pressure. It has been shown that the well-known barrel erosion issue is mostly due to the aggressive abrasion of the cartridge metal by the hot plasma jet. A new cartridge concept has been especially designed to overcome this problem. Results are very satisfactory

Dynamic Punch Shear Characterization of Twill Weave Graphite/Epoxy Composites

In this study, the high strain rate response of twill weave graphite/epoxy composites under punch shear mode was characterized. 24-layer laminates of twill weave graphite fabrics were fabricated using a relatively inexpensive vacuum assisted resin infusion moulding process (VARIM) with a low viscosity SC-15 resin system. Samples of nominal size 25 by 12.7 by 4 mm were cut from the laminates for high strain rate testing. High strain rate punch shear tests were carried out with a modified Split Hopkinson Pressure Bar setup. Samples were loaded in punch shear mode through the thickness. Varying the breech pressure allowed testing at different strain rates in the range of 1400/s to 3800/s. Samples were tested at room and three elevated temperatures of 52 °C, 79 °C and 107 °C. The samples exhibited increasing peak shear stress with increasing strain rate at all temperatures. However, the peak stress decreased with temperature for a given range of strain rates. Failure modes were characterized with scanning electron microscopy, which revealed the degradation of the fibre-matrix interface with increasing temperatures.

Computation of In-bore Velocity-time and Travel-time profiles from Breech Pressure Measurements

The paper describes breech pressure measurement and also discusses the computation of velocity-time and travel-time profiles in the barrel from the instantaneous breech pressure values. The computed value of velocity at the shot out instant is obtained as the muzzle velocity. A close correlation is observed between the muzzle velocities measured by a radar and those computed from pressure-time data by this method.

Penetrator launch diagnostics from breech pressure measurements duringoperation of an air cannon

We report breech pressure measurements during the firing of an aircannon. We find that the pressure record is a useful and convenient diagnosticof the penetrator projectile motion during launch - supplementing or replacingbeam- or wire-breaking speedometers and on-board accelerometers. With littleeffort, launch speed can be measured with a 2σ error of 1.75 m s-1or better than 5%.

Theoretical modeling of the interior ballistic processes in an electrothermal chemical gun

A comprehensive theoretical model has been developed to describe the interior ballistic processes in an electrothermal chemical (ETC) gun. The model, which takes into account the plasma/working fluid interaction, predicts transient and spatial variations of the gun chamber pressure, instantaneous projectile motion, and gun muzzle velocity. A complete set of governing equations is derived from first principles of physics, and the governing system is solved by an implicit finite difference scheme. Two sets of pulse-forming network (PFN) discharge curves, with various peak power times and total discharge times; are employed to study the ETC gun performance. The numerical results show that a ballistic efficiency of more than 13% can be achieved for an exothermic working fluid (C8H18/H2O2). The breech pressure and projectile-base pressure exhibit double peaks during the ballistic cycle. The first peak is due to the initial discharge of a plasma jet into the gun chamber, whereas the second peak is the result of vigorous interactions between the plasma jet and the working fluid. The calculated maximum breech pressure is on the order of 400 MPa, and a typical muzzle velocity is on the order of 2 km/s. Comparison of present numerical results with limited available experimental data is made and found to be good.

Development of a Two-Stage Pellet Injector for Heliotron-E

A two-stage pellet injector for Heliotron-E is constructed and tested. The aim is to increase pellet velocity for more flexible density profile control of the Heliotron-E plasma and also to conduct a pellet ablation study using a wider range of pellet velocity. The pellet velocity is limited to ∼1.4 km/s in the current six-pellet injector at Heliotron-E. The fundamental operation is simulated with the Quickgun code. The experimental results generally agree well (within 80 to 90%) with the code calculations. By using a newly developed high-pressure fast valve, a hydrogen pellet velocity of 3.2 km/s has been achieved without a supportive shell or sabot to protect the pellet, although more tests are needed to confirm whether pellets can reliably be accelerated to this high speed without fracturing. The dependence of the pellet velocity and breech pressure on the pump tube fill pressure is studied. The results show that the fill pressure is an important parameter. The effect of the clearance between the piston and the pump tube wall on the pellet velocity is also investigated. The wear and damage of the piston caused by the compressing propellant gas are investigated. It is shown that changes on the piston surface when hydrogen is used for fill gas are different from the case of helium.

Numerical analyses of breech pressure chambers with cavities or semi-elliptical cracks

Numerical failure analyses are presented for jet engine starter's breech pressure chambers. Several models with and without semi-elliptical flaws are investigated by using a three-dimensional elastic-plastic finite element program. Some results are compared with the corresponding experimental strain measurements. These analyses provide yielding and burst pressure, and other information which relate to the cause of the premature failure in the breech pressure chambers. A slight modification in the geometry of the cylindrical pressure vessel with quasi-spherical head is shown to drastically reduce the yielding and burst pressures especially for large pre-existing semi-elliptical cracks.

Subsonic single-phase flow in a gun simulator

Reported here are the time-resolved and ensemble mean and rms fluid velocities obtained by laser Doppler anemometry in a subsonic gun simulator with an inert single-phase flow and a projectile exit velocity of 40 m/s. The results presented also include the time-resolved measurements of the projectile velocity and breech pressure. The results show that, based on measured breech-pressure record, the calculated projectile velocities are almost exactly equal to the measured values and confirm that the friction of the system is negligible. Fluid velocity traces, together with ensemble mean and rms velocity profiles, indicate the presence of a wall boundary layer occupying up to 20% of the tube radius and having a growth rate similar to that of steady turbulent boundary layers. The nature of velocity fluctuations and the shape of velocity profiles inside the boundary layer also suggest that the boundary layers are turbulent in the wake of the projectile.

Development of a hydrogen electrothermal accelerator for plasma fueling

We have developed a prototype high-velocity pneumatic pellet injector that uses hydrogen plasma propellant generated in a high-current arc discharge. A single-barrel pneumatic pellet gun has been fitted with a cylindrical arc chamber interposed between the hydrogen propellant inlet valve and the gun breech. The chamber incorporates a ceramic insert for generating vortex flow in the incoming gas stream, which provides azimuthal arc stabilization. The arc is initiated after the propellant valve opens and the breech pressure starts to rise; a typical discharge lasts 150–300 μs with peak currents up to 2 kA. The gun has been operated with 4-mm-diam, 6- to 11-mm-long deuterium and hydrogen pellets. At 100-bar plenum pressure (hydrogen propellant), the arc characteristics are 〈V〉=350–800 V, 〈I〉=600 A, so that 60–150 J of electrical power is dissipated. Pellet speeds increase by 300 to 600 m/s depending on the projectile mass, which typically represents a 10-J increment in the pellet kinetic energy. Velocities up to 1.7 km/s for deuterium pellets and 2.0 km/s for hydrogen pellets have been achieved. Comparing these data to muzzle velocities calculated from idealized one-dimensional compressible flow gun theory demonstrates that substantial propellant heating, resulting in increased propellant sound speed, has been achieved.