Search

Because of its excellent insulation capability, the usage of a silica-phenolic charring ablator as a nozzle liner is a common practice in the solid rocket motor industry. During the design of a solid rocket motor employing a silica-phenolic nozzle liner, it is desired to conduct an accurate analysis yielding in-depth thermal response and recession characteristics. As the interior ballistics and nozzle recession rate mutually interact, the best practice is to perform a coupled solution to both. Commonly used one-dimensional analysis tools with empirical approaches for estimation of convective heat transfer rate and blowing effect generally lack sought accuracy and do not model the transient shape-change phenomenon, which affects the nozzle performance. This Paper considers governing equations for charring, including pyrolysis gas injection and surface energy balance for melting ablation, along with a boundary condition governed by interior ballistics, and demonstrates a framework in which these equations are solved with governing equations for the nozzle flowfield in a coupled manner. Development and validation of a one-dimensional material response solver based on the same governing equations is also demonstrated. Also, results from a static firing test conducted with a small-scale ballistic evaluation motor employing a silica-phenolic nozzle insert are provided. Results from both investigations are compared and discussed.

During their operation, solid rocket boosters experience axial stresses caused among other things also by fluid mechanical loads from the internal flow. The accurate prediction of the flowfield is ...

This work presents a novel approach for the modeling of the entrainment in the numerical simulation of the internal ballistics of hybrid rocket engines with paraffin-based fuels. This model, coupled with a more sophisticated gas–surface interaction treatment, is an improvement of the model previously developed by some of the authors, which was based on some oversimplifying assumptions. Indeed, the old entrainment model was performed in a close range of averaged oxidizer mass flux, and it made the overall numerical model not scalable on different motor sizes. Therefore, a new correlation is introduced, which is based on the Reynolds number and takes into account the dependence of the entrained fraction on the shear stress exerted by the gas flow and the tube diameter. Firstly, the new and the old numerical models are compared in order to highlight the improvement obtained by the current efforts. Then, the model has been validated on experimental tests involving two different thrust class motors. Finally, the effect of the motor size on the fuel consumption is shown, thus revealing the crucial influence of the recirculating zone extension due to the oxidizer axial injection.

In order to achieve multi-objective optimization design of ballistics and improve the power of weapons, an optimization model for the internal ballistic simulation design of the propellant charge was established. Based on the requirements of artillery ballistic performance, the model took several influences into account, such as type, charge mass (ω) and web thickness (2e1). The objective function was composed of muzzle velocity (v0), maximum chamber pressure (pm), relative burnout point (ηk) equations. The computational program used recursive algorithm to calculate and select reasonable charge results by looping the internal ballistics and optimization design equation sets. 105 mm artillery and 122 mm artillery were selected as examples to optimize the charge design. The results show that compared with the existing charging scheme, the loading scheme optimized by the model can reduce the relative burnout point of 105 mm artillery by 0.21 in the case of the muzzle velocity, and the maximum chamber pressure have a little difference. The maximum chamber pressure of the 122 mm artillery reduces by 2.83% while the muzzle velocity increases by 1.13%.

A novel internal ballistics technique for determining the time-resolved spatially averaged regression rate of the solid-fuel grain in a hybrid rocket engine is presented. This technique makes use o...

An unsteady quasi-one-dimensional flow solver for simulating internal ballistics and axial acoustic fluctuations in solid rocket motors is presented in this paper. Higher-order numerical solutions of quasi-one-dimensional governing equations are prone to numerical oscillations due to the nonconservative form of the governing equations and the nonsmooth axial variations of the cross-sectional area. Adding artificial dissipation to a central scheme is found to be inadequate for suppression of such oscillations, and so a simple low dissipation shock-capturing scheme (named SLAU2) is used instead. The inherent numerical dissipation of this scheme is helpful in the proper capturing of steep-fronted acoustic waves (that develop at the onset of triggered instabilities) without undesirable numerical damping of the acoustic waves. Using the new solver, a procedure for computing characteristic frequencies, corresponding mode shapes, and damping rates is proposed and validated for a motor with a cylindrical grain ge...

In this paper, we present a novel numerical approach for predicting the fluid flow in a solid rocket motor chamber with burning propellant grain. We use a high-order technique to track the regressing grain surface. Spectral convergence toward the exact burning surface is achieved thanks to Fourier differentiation. For the computation of the internal chamber fluid flow, we make use of a body-fitted volume mesh deforming with the grain surface. We describe several methods to deform the volume mesh and to keep good mesh element quality without global remeshing. We then couple the surface and volume approaches and integrate them into a complex code for compressible, multispecies, turbulent flow simulations. Thanks to these methods, we are able to exhibit one of the first three-dimensional simulations of the internal flow in a realistic solid rocket motor coupled to complex grain surface regression. In prior work, burning grain surface methods have only been coupled with one-dimensional internal ballistics sol...

In solid rocket motors, a strong bond at the propellant–liner interface ensures that the propellant functions as designed. If the interface degums, the propellant burn surface area will change and the performance of internal ballistics will be adversely affected. In this study, two cases of motor failure are considered to investigate methods for improving the bond strength between the propellant grain and the liner interface, with the aim of achieving a tensile strength exceeding the 8 kg/cm2 requirement. Hydroxyl-terminated polybutadiene was used as the liner material. This hydroxyl-terminated-polybutadiene-based material was conditioned and processed under the conditions of 5–20 torr pressure and 60–70°C temperature. Further, toluene diisocyanate was considered as the hardener and its contents were increased in the liner by 0 (i.e., original content), 2, 5, 10, and 15% to obtain diisocyanate NCO/OH equivalence ratios of 1.035, 1.057, 1.087, 1.144, and 1.187, respectively. Thereafter, bond strength test...

A computational thermofluid-dynamic model of hybrid rocket internal ballistics is developed. Numerical simulations of the flowfield in a laboratory small-scale hybrid rocket motor, operated with gaseous oxygen and high-density polyethylene propellants, are carried out with the aim of predicting the solid fuel regression rate experimentally achieved with two different oxidizer injectors. The fuel regression rate is the main parameter for the hybrid rocket design. Here, it is calculated with a detailed gas/surface interface characterization based on local mass and energy balances. The combustion of oxygen and gaseous ethylene injected from the fuel wall is modeled by means of the probability-density-function approach coupled to chemical equilibrium. Two oxidizer-injection configurations, which generate either a two-dimensional axially symmetric or three-dimensional flowfield, are analyzed. The local regression rate is evaluated along both the fuel grain axis and inner circumference in the three-dimensional case, as well as at several stages in the firing, by updating the local port diameter, which is thus not assumed constant. Data retrieved from three firing tests are compared with the numerical results, revealing good agreement between both the average regression rates (maximum deviation less than 5%) and the fuel consumption axial profiles (with maximum deviation of 14%)

The influence of initial propellant temperature on solid propellant rocket motor performance is examined in the present study, with the focus primarily on predicted steady and nonsteady burning rate behavior. The present evaluation includes an examination of quasi-steady burning of a conventional composite propellant under pressure, core flow (erosive burning), and normal acceleration (say, due to motor spinning). The most direct and well-known influence of initial propellant temperature is on the pressure-dependent burning rate. The pressure-dependent burning rate, as the base burning rate, in turn influences the degree of augmentation seen under core flow and normal acceleration; in general, the lower the base rate, the higher the augmentation. The explicit presence of initial propellant temperature in various model equations for the flow- and acceleration-dependent burning components, and the corresponding effect of the initial temperature on the propellant’s burning surface temperature, can produce an...

A numerical rebuilding of a series of test data obtained with static firings of a lab-scale hybrid rocket is carried out with a Reynolds-averaged Navier–Stokes solver including detailed gas–surface interaction modeling based on surface mass and energy balances. Two experimental campaigns are considered in which gaseous oxygen is fed into axisymmetric hydroxyl-terminated polybutadiene grains through an axial conical subsonic nozzle. A validation rebuilding of all of the firing tests has been performed first to highlight numerical prediction capabilities and modeling limits. Despite the several geometrical simplifications, which allows using a reduced number of cells in the computational domain and thus performing parametric analyses efficiently, the present computational fluid dynamics approach is able to capture the main features of the motor internal ballistics, fairly reproducing the average chamber pressure values and the fuel regression rate trends with oxidizer mass flux and port diameter. Computed f...

Internal ballistics simulations of solid rocket motors have been conducted with the propellant grain's 3-D burning surface geometry described by a new minimum distance function approach and the internal flowfield represented by 1-D, time-dependent, single-phase compressible flow equations. The combustion model includes erosive burning and unsteady, dynamic burning corresponding to transient energy storage in the heated surface layer of the propellant. The integrated internal ballistics code (Rocballist) is used to investigate the role of these two burning rate augmenting mechanisms in solid rocket motor performance. Two tactical motors are used as test cases. Results indicate that dynamic burning can be the dominant factor in producing a short-duration ignition pressure spike in low-L* motors, particularly if the L/D ratio is not too large and the port cross section is nonrestrictive (e.g., center perforated grain). However, when L/D is large and the port cross section is noncircular in the aft section (aft fins/slots), erosive burning can take over in dominating the burning rate to the extent that an otherwise progressive pressure-time trace becomes regressive/neutral. That is, erosive burning can effectively prolong the initial pressure spike in some star-aft motors. The results also show that with sufficiently accurate models of dynamic burning and erosive burning, it is reasonable to expect reliable internal ballistics predictions with suitable simplified flowfield models, thereby realizing significant reductions in computation time compared with 3-D, multiphase reacting flow simulations.

A direct numerical simulation (DNS) of a homogeneous ammonium perchlorate/hydroxyl-terminated polybutadiene solid propellant in crossflow was carried out to provide proper boundary conditions to an interior ballistics model. A two-step global finite-rate chemistry model for ammonium perchlorate decomposition and decomposition gas-binder gas reactions was used. An Arrhenius pyrolysis model was used to describe the propellant regression rate. Using strand burn rate data, the DNS model was calibrated by modeling an environment with no crossflow and adjusting thermodynamic properties in the gas/solid to match the measured regression rate. Crossflow Mach numbers were then induced, ranging from At = 0.0 to 0.8, where the calculated regression rates are compared to the base regression rate at M = 0.0. The analysis shows that near-wall vorticity increases with Mach number, but does not significantly reduce the flame to wall stand-off distance. Temperature gradients due to boundary layer compression are shown to dominate the regression rate. The validity of the results was tested by incorporating them into an interior ballistics model to simulate the performance of an actual rocket motor and compare to static test data. A simplified DNS heat-transfer-based analysis is presented and shown to produce similar conclusions.

This paper describes the design of an 8-MJ base-pushed launch package for railgun launch. Extensive interior ballistics and flight dynamic analyses were performed. The launch package was designed to withstand a peak acceleration of 57 k-gees, and a substantial amount of lateral load. The lateral load was of prime importance for this launch package to ensure survivability of subprojectile joints present inside. Even though the launch was by a base-push method, a sabot was necessary to carry the bore-riders. Sabot separation dynamics and projectile aerodynamic coefficients were evaluated to ensure a successful flight. The package was successfully tested at the 32-MJ UK EM Gun Facility located at Kirkcudbright, Scotland at 7-MJ muzzle energy.

The nonsteady internal ballistics of a star-grain solid-propellant rocket motor are investigated through a numerical simulation model that incorporates both the internal flow and surrounding structure. The effects of structural vibration on burning rate augmentation and wave development in nonsteady operation are demonstrated. The amount of damping plays a role in influencing the predicted axial combustion instability symptoms of the motor. The variation in oscillation frequencies about a given star grain section periphery, and along the grain with different levels of burnback, also influences the means by which the local acceleration drives the combustion and flow behaviour.

Analyses of internal ballistics and criteria for reaction propagation in nonelectrical tube explosive lines were performed based on explosive loading density, average particle size, and typical geometry using an approach based on heat transfer and decomposition kinetics in the explosive particles in quasi steady state. The results indicate the existence of a critical or maximum average explosive particle size for a given explosive loading density beyond which sustained propagation may cease. Large variations usually exist in the explosive loading density, so that fine particle sizes below 20 μm are preferable. Fine particle size also may increase the adhesion to the inner tube wall for mitigation of powder migration problems. Computer simulations of detonating end tip to nondetonating end tip transfer were performed using the CTH hydrodynamic code developed by the Sandia National Laboratories. Preliminary results indicate that the hot gas from the detonating end tip is more effective for initiating pyrotechnics in the nondetonating end tip and that a larger gap between the end tips is essential for the success of hot gas initiation

The first known gun barrel thermochemical erosion modeling code is presented. This modeling code provides the necessary missing element needed for developing a generalized gun barrel erosion modeling code that can provide analysis and design information that is unattainable by experiment alone. At the current stage of code development, single-shot comparisons can be made of either the same gun wall material for different rounds or different gun wall materials for the same round. This complex computer analysis is based on rigorous scientific thermochemical erosion considerations that have been validated in the reentry nosetip and rocket nozzle community over the last forty years. The 155-mm M2O3 Unicannon system example is used to illustrate the five module analyses for chromium and gun steel wall materials for the same round. The first two modules include the standard gun community interior ballistics (XNOVAKTC) and nonideal gas thermochemical equilibrium (BLAKE) codes. The last three modules, significantly modified for gun barrels, include the standard rocket community mass addition boundary layer (TDK/MABL), gas-wall chemistry (TDK/ODE), and wall material ablation conduction erosion (MACE) codes. These five module analyses provide recession, temperature, and heat flux profiles for each material as a function of time and axial position. In addition, this output can be coupled to PEA cracking codes. At the peak heat load axial position, predicted single-shot thermochemical wall erosion showed uncracked gun steel eroded by a factor of one hundred million more than uncracked chromium. For chromium plated gun steel, with its associated crack profile, it appears that gun steel ablation at the chromium cracks leaves unsupported chromium, which is subsequently removed by the high-speed gas flow

Structural analysis is a critical aspect in the successful design of tube launched projectiles, such as mortar rounds. Ongoing research conducted at West Virginia University has focused on a Hybrid Projectile (HP), folding-wing UAV design inspired by mortars. This has driven the necessity of a structural analysis of the prototype design to provide vital feedback to designers to ensure that the HP is likely to survive the act of launching. Due to the extreme accelerations during the launching phase, a typical mortar round experiences dramatic impulse loads for an extremely brief duration of time. Such loads are the result of the propellant combustion process. Thermodynamic-based interior ballistic computations have been formulated and were used to solve the dynamic equations of motion that govern the system. Modern ballistic programs solve these equations by modeling the combustion of the propellant. However, mathematical procedures for such analyses require complex models to attain accurate results. Consequently, the objective of this research was to create a ballistic program that could evaluate interior ballistics by using archived pressure-time data without having to simulate the propellant combustion. A program routine created for this purpose reduces the complexity of calculations to be performed and minimizes computational effort, while maintaining a reasonable degree of accuracy for the motion dynamics results (temporal position, velocity, acceleration of the projectile). Additionally, the program routine was used to produce a mathematical model describing the pressure as a function of time, which could be used as loading conditions for more advanced explicit-dynamic finite element simulations to evaluate the transient response and stress wave propagation of the prototype and individual payload components. Such simulations remove uncertainties related to the transient loads needed to assess the structural integrity of the projectile and its components.

The Sandia Hypervelocity Launcher (HVL) uses impact techniques on a two-stage light-gas gun to launch flier plates to velocities in excess of 10 km/s. An important problem in designing successful third stage techniques for impact launching fliers to such velocities is detailed understanding of the interior ballistic performance of the third stage. This is crucial for preventing melt and fracture of the flier plates during the extraordinary accelerations that they undergo (accelerations on the order of 10{sup 9} g are typical on the HVL). We seek to optimize HVL launch conditions in order to achieve two major goals: first, to maximize the potential launch velocity for a given flier, and second, to allow different flier configurations. One tool that we can apply in studying HVL performance is the use of multi-dimensional wave propagation codes. We have used such codes, particularly the Sandia Eulerian code CTH, to study a variety of interior ballistics issues related to gun performance and launcher development for almost ten years. Recently this work has culminated in a major contribution to HVL design, namely the capability to launch ``chunk`` fliers. `Me initial phases of design development were solely devoted to CTH computations that studied potential designs, identifiedmore » problems, and posed possible solutions for launching chunk fliers on the HVL. Our computations sufficiently narrowed the design space to the point that systematic experimental progress was possible. Our first experiment resulted in the successful launch of an intact 0.33 gram titanium alloy chunk flier to a velocity of 10.2 km/s. The thickness to diameter ratio of this flier was approximately 0.5.« less

Electrothermal-chemical (ETC) guns offer the prospect of significantly increased muzzle kinetic energy over conventional solid propellant gun systems as evidenced by experimental data collected over the past several years. To support the various experimental programs, codes developed specifically for ETC interior ballistic processes have matured including 0D, 1D, and 2D/3D models. Although these models in general have been successfully applied to simulate experimental data, prediction of gun interior ballistic performance at high gun energies has been more difficult. In this paper we examine comparisons of 0D and 1D model results with experimental data in order to gain a clearer understanding of the way that electrothermal energy input modifies the interior ballistics in ETC guns. These comparisons suggest that both axial and radial effects must be considered, necessitating development of first-principles 2D/3D models. Results from one such model, CRAFT, are presented in the paper. >

In the design and development of solid propellant rocket motors, the use of numerical tools able to predict the behavior of a given motor is particularly important in order to decrease the planning times and costs. This paper is devoted to present the results of the internal ballistics numerical simulation of the NAWC tactical motor n. 6, from ignition to burn-out, by means of a quasi-one-dimensional unsteady numerical simulation model, SPINBALL, coupled with a three-dimensional grain burnback model, GREG. In particular, the attention is focused on the effects on the SRM behavior of the erosive burning, total pressure drops and the cause of the pressure overpeak occurring during the last part of the ignition transient. The final objective is to develop an analysis/simulation capability of SRM internal ballistics for the entire combustion time with simplified physical models, in order to have reduced the computational costs, but ensuring an accuracy greater than the one usually given by zero-dimensional models. The results of the simulations indicate a very good agreement with the experimental data, as no attempt of submodels calibration is made, enforcing the ability of the proposed approach to predict the SRMs internal flow-field conditions. The numerical simulations show that NAWC n. 6 internal ballistics is completely led by the erosive burning, that is the root cause of the pressure peak occurring immediately after the SRM start-up.

Analysis of the interior ballistics is essential for the development of gun or propellant configurations. The granular solid propellants with high energy and fast burning rate produce a large thrust in extremely short time intervals. For the study of these, therefore, it is necessary of a numerical code for the two-phase flow of the interior ballistics. Recently, an interior ballistics code (IBcode) for the two-phase flow using the Eulerian-Lagrangian approach has been developed. The SIMPLE algorithm and the SMART scheme have been used for the IBcode. The ghost-cell extrapolation method has been used for the moving boundary with the projectile movement. In this study, a performance of the interior ballistics according to the position of the solid propellant in the chamber has been investigated using the IBcode. In previous researches, propellants had been evenly distributed in the chamber. In this study, however, three cases of the existence of empty space in the chamber at which the propellants are not evenly distributed have been considered; Propellants are located in the region near the base, propellants in the region near the breech, and propellants in the center of the chamber, respectively. The 7-perforated configuration of the solid propellant has been used in this research. The results have shown the performance variations of the interior ballistics according to solid propellant position in the chamber. The cases of the propellants located in the region near the base and breech have shown that the value of the negative differential pressure and the difference between the breech pressure and the base pressure are much higher than those of the propellants located in the center of the chamber. The case of the propellants in the center of the chamber is, therefore, more profitable to improve the performance of the interior ballistics.Copyright © 2011 by KSME

This article proposes a physical model for liquid quench of solid rocket motor and presents the results of experimental study. It is found that there is a critical value of injection pressure drop during liquid quench of solid rocket motor. The critical value of injection pressure drop increases with propellant energy (gy). The additive selected appropriately added in liquid is able to reduce significantly the liquid quantity required (LQR) Ws, for extinction of solid rocket motor. LQR reduced by the addition of 0.5% CE by weight in water are about 35 and 25% for double base propellant and nonmetalized polyurethane-ammonium perchlorate composite propellant, respectively. LQR is mainly dependent upon the propellant energy, i.e., it increases with increasing propellant energy. For pure water, Ws * O.lg^and for water + 0.5% CE, Ws * 0.76gy* The variation of LQR with the chamber pressure is related to pressure exponent of propellant (n). If n > 0, it increases with increasing chamber pressure; and if n < 0, it decreases with increasing chamber pressure. With the injection pressure drop increasing, LQR decreases and the depressurization rate of solid rocket motor increases, respectively. The experimental results and the analysis indicate that the theoretical study on liquid quench of solid rocket motor should include the coupling effects of transient burning of propellant, heat transfer of liquid jet impinged on burning surface, evaporation of liquid droplets, and internal ballistics of rocket motor.

A multidimensional, transient, fluid dynamic model, BISON, has been developed to study the interior ballistic processes in an electrothermal-chemical (ETC) gun. The model solves the full Navier-Stokes equations and uses a high-order numerical scheme to integrate the governing equations. Most of the important physical processes pertinent to ETC gun interior ballistics, including multiphase flow, chemical reaction, and plasma dynamics, are incorporated in the model. Examples of model applications to study basic ETC gun phenomena, such as plasma jet penetration and real gun design component analyses, are presented and discussed. The modeling results not only compare well with experimental data but also provide a better understanding of the interior ballistics physics. The multidimensional model BISON proves to a very useful tool for ETC gun interior ballistics simulations. >

Experimental gun firings and computer simulations of hybrid solid propellant-electrothermal gun propulsion concepts are reported. The test firings were conducted using loose and compacted ball propellant in a 30-mm test fixture. A plasma capillary located at the breech of the gun was used both to ignite the propellant charge and to augment the ballistic process. Computer simulations of selected tests were conducted using modified lumped parameter interior ballistic models, which were originally developed for conventional charge simulations. More general optimization studies of the solid propellant electrothermal-chemical interior ballistic process are also discussed. >

To solve problems of low efficiency, long period and not handling coupling in solid rocket motor traditional design, multidisciplinary design optimization method of solid rocket motor was specified through comparison of typical MDO method and multi-objective collaborative optimization model of solid rocket motor MDO was constructed. Aiming at computation difficulties of CO, paper put forward some approaches to solve the problem. Finally, to reduce solid rocket motor computation expense, three most important disciplinary approximate analysis model of shell, thermodynamic calculation and interior ballistics model were formulated. This research will be valuable for solid rocket motor design using MDO theory.

Base on the launch mechanism and structure characteristic of rarefaction wave gun, interior ballistic gas dynamic model of it applying the inertial breech that considering the dynamic opening process of went equipment is established. By calculating the model the distribution of interior ballistic parameters in the launch process are also discussed, and then by contrasting the distribution of press, temperature, recoil force and recoil momentum of the same type general gun. It is concluded that rarefaction wave gun can extremely reduce recoil momentum to 88.3% and reduce the barrel temperature to 34.1% without effect the muzzle velocity under the same loading condition.

The study of forensic ballistics can be divided into four fields of study, namely, internal, intermediate, external, and terminal ballistics. Internal ballistics deals with the events that take place within the firearm. Intermediate ballistics covers a transition phase between internal and external ballistics and occurs around the muzzle of the firearm. External ballistics deals with the trajectory of the projectile between the muzzle of the firearm and the target. External ballistics covers the various factors that have an influence on the flight of a projectile. Terminal ballistics is a study of the projectile's impact with the target. Terminal ballistics looks at the effects that the projectile has on the target and the effects that the target has on the projectile. When the target is a person, the term wound ballistics is more appropriately used. Keywords: internal ballistics; intermediate ballistics; external ballistics; terminal ballistics; wound ballistics; range determination; firearm examination; GSRs; gunshot residues

A precision guided projectile that can strike a target with high accuracy is of interest. The accomplishment of the goal involves multidisciplinary studies starting from interior ballistics, launch dynamics, exterior ballistics through terminal effects. One of the critical requirements relies on reliable and survivable guidance, navigation, and control devices, which are expected to function after exiting a gun barrel. A flare-stabilized projectile test bed, which was designed to accommodate a sensor pack in the coned space of the tail, was studied. The sensor pack consisted of a few composite boards which carry sophisticated sensors and processors. The mounted electronic devices are encapsulated with epoxy potting material in the container. A 57-mm smoothbore gun barrel, which has a total length of 2440 mm, was used to simulate the projectile launch. The projectile system, which had a total mass of approximately 1.26 kg, was composed of alloy steel body, aluminum flare and pusher plate, nylon sabot and obturator. Due to desired high-speed velocity at the muzzle, the projectile system was designed to withstand an immense base pressure for a short period of time. The transient excitation that gives rise to significant pressure waves propagating through onboard electronic components is of concern. The attempt of this paper is to conduct preliminary firing survivability analysis of the onboard components for a tactical projectile system.

A new species of gun (Rarefaction wave gun) propulsion that dramatically reduce recoil momentum and heat imparted to the future cannons during firing. The method may be considered a hybrid propulsion technology with features common to both closed-breech cannons and recoilless rifles. A new interior ballistics model is presented, which may better be understood. Expatiated and argued contents as follow: background and meaning of study the task, the theory and numerical simulation of interior ballistic based on modern two-phase flow theory.

Recent requirements for hypervelocity projectile launch for strategic U.S. Army missions have led to the proposal of a variety of gun propulsion systems. Among these systems are those that utilize solid propellant along with electrothermal-chemical (ETC) augmentation. Advanced solid propellant systems with complex grain geometry and loading configuration are also being investigated. In response to this need, the U.S. Army Research Laboratory (ARL) has, for a number of years, engaged in the study of solid propellant ignition using a hot, low molecular-weight plasma generated by ETC means. In addition, ARL is developing an ETC modeling capability using the next-generation interior ballistics code, NGEN, and a series of experimental studies in a ballistic simulator to generate code validation data. The current report demonstrates progress for application of the NGEN code to solid propellant, direct-fire gun systems in which various propellant configurations (i.e., grains and disks) are combined into a single charge in order to obtain higher-loading densities. The charge is ignited using the efflux from an ETC plasma capillary made of polyethylene. Comparison with pressure data measured in a 25-mm ballistics simulator, filled with disks of JA2 propellant as the main charge and a small amount of inert grains as filler, provides validation of the NGEN model with respect to the representation of the plasma efflux from an ablation capillary, into the chamber, and around propellant disks.

Recent requirements for hypervelocity projectile launch for strategic U.S. Army missions have led to the proposal of a variety of gun propulsion systems. Among these systems are those that utilize solid propellant along with electrothermal-chemical (ETC) augmentation. Advanced solid propellant systems with complex grain geometry and loading configuration are also being investigated. In response to this need, the U.S. Army Research Laboratory, in cooperation with Paul Gough Associates, is developing the Next Generation Interior Ballistics model, NGEN. The goal of this project is the development of an advanced interior ballistics model for use in the design and investigation of both indirect-and direct-fire gun propulsion systems. The current report demonstrates progress for application of the NGEN code to solid propellant, direct-fire gun systems in which various propellant configurations (i.e., grains and disks) are combined into a single charge in order to obtain higher-loading densities. The charge may be ignited using either a conventional (Benite) or an ETC plasma capillary. These notional charges are being investigated to determine code performance and assess the need for code upgrades, as well as to investigate propellant ignitability with Benite and plasma sources. Comparison with pressure data measured in a 25-mm ballistics simulator, filled with inert disks and grains, provides validation of the NGEN model with respect to the representation of the plasma efflux from an ablation capillary, into the chamber, and around propellant disks.

Despite many decades of study, new solid rocket motor systems frequently experience unsteady gas motions and associated motor vibrations. This phenomenon most often occurs when a combustion chamber’s acoustic modes couple with combustion/flow processes. Current linear models of the sort used in the Standard Stability Prediction program (SSP) are designed to predict the tendency for a SRM to become unstable, but they do not provide any information on the severity of the instability (usually measured by the limit cycle amplitude of the oscillations) or on the triggerability (the tendency of an otherwise stable system to oscillate when pulsed with a sufficiently large disturbance) of the system. The goal of our present work is to incorporate a nonlinear capability into the JANNAF Solid Performance Program (SPP’04TM), a grain design and ballistics code maintained by Software and Engineering Associates, Inc. (SEA). SEA has encoded a new nonlinear model into SPP’04TM that allows for an interaction between the combustion instability and the mean internal ballistics. This approach yields both a DC shift in the mean chamber pressure and a limit in the amplitude of the oscillatory pressure. The enhanced capability of the SPP’04TM is demonstrated by comparing the experimental and numerical chamber pressure histories of a pulsed solid rocket motor.

The U.S. Army is exploring a variety of armament propulsion options for indirect- and direct-fire weapons to be employed in the legacy force and for the Future Combat System (FCS). Development of propelling charges for these weapons requires state-of-the-art physics-based modeling codes. The gun propulsion-modeling environment has traditionally been one in which independently developed and upgraded computer codes were used to analyze different propulsion techniques. with no single maintainable code able to evaluate several candidate system. This situation rendered comparison of ballistic performance for various weapon options cumbersome and inconclusive. In direct response to this situation. the U.S. Army Research Laboratory (ARL) has developed a "next-generation" computer scaleable. three-dimensional, multi-phase, computational fluid dynamics code for armament propulsion (interior ballistics) modeling.

The Army Research Laboratory has developed a scaleable, 3D, multiphase, computational fluid dynamics (CFD) code with application to gun propulsion (interior ballistics) modeling. The NGEN3 code, which incorporates general continuum equations along with auxiliary relations into a modular code structure, is readily transportable between computer architectures and is applicable to a wide variety of gun propulsion systems. Two such systems are the Army's Modular Artillery Charge System (MACS) and the Future Combat System (FCS). The MACS is being developed for indirect fire cannon on both current and developing (e.g., Crusader) systems. The efficiency of the MACS charge is dependent on proper flamespreading through the propellant modules; a process that has been repeatedly demonstrated in gun firings, successfully photographed using the ARL ballistics simulator, and numerically modeled using the NGEN3 code. The FCS requires weapons systems exhibiting increased range and accuracy. One of the technologies under investigation to achieve these goals is the electrothermal-chemical (ETC) propulsion concept, in which electrically generated plasma is injected into the gun chamber igniting the high-loadingdensity (HLD) solid propellant charge. NGEN3 code development and application to the MACS and FCS is currently a DoD HPC Challenge Project (No. 112) and is being greatly advanced by access to the DoD high performance computers (HPCs). Associate Fellow AIAA. Propulsion Physics Team Leader, Ballistics and Weapons Concepts Division, Weapons and Materials Research Directorate. Mechanical Engineer, Propulsion Physics Team, Ballistics and Weapons Concepts Division, Weapons and Materials Research Directorate. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. INTRODUCTION A solid propellant gun system consists of a reaction chamber connected to a gun tube through which a projectile is guided once propelled by pressurization of the chamber. Chamber pressurization is accomplished by placing a solid propellant (SP) charge in the chamber and igniting it by various means. Current SP charges are generally complex structures consisting of hundreds or even thousands of distinct regularly formed (e.g., spherical, cylindrical) grains, which may be loaded in either regular or random arrangements. In addition to small-scale voidage between grains (i.e., porosity) many charges also contain large-scale voidage (i.e., ullage), which surrounds the entire charge (such as when the charge does not fill the entire chamber volume) or separates distinct subcharges (i.e., increments or modules) that together comprise the whole charge. The addition of energy to the chamber, usually near the gun breech, or rearmost end of the chamber, and in some cases through a tube extending along the centerline of the chamber, ignites the SP. In general, all of the grains are not ignited simultaneously, but an ignition flame spreads from the breech to the projectile base. The burning of the SP transforms chemical energy into heat as hot gases evolve from the surface of each grain of propellant. Initially the projectile resists movement allowing the pressure in the chamber to climb rapidly. Since the burn rate of the propellant is proportional to the pressure, hot gases are produced at an accelerated rate until peak pressure is reached in the chamber. Movement of the projectile down the gun tube, usually slight before peak pressure and much more significant afterwards, causes the chamber volume to increase, and generates rarefaction waves, which lower the pressure and thus the burn rate of the propellant. Upon ignition and burning, the gas dynamic flowfield in the gun chamber takes on a highly complex structure that includes the dynamics of propellant motion and combustion and various gas dynamic flow phenomena such as turbulent mixing, highly transient pressure waves, steep gradients in porosity and temperature, nonideal thermodynamics, and gas generation.

Introduction T HE solid rocket motor (SRM) ballistician has the job of predicting the chamber pressure and thrust history for both new and existing motors utilizing propellant burning rate and grain geometry, ambient conditions, and nozzle geometry. For motors which do have a test history, ballisticians introduce a constant "scale factor" to force predictions to match actual burn times of test units as well as a time varying multiplier to improve "pointwise" matching of the pressure history. This pointwise burning anomaly rate factor, or BARF, is usually established as a function of web distance since it is generally acknowledged that the factor accounts for spatial burning rate variations within the grain. This ubiquitous quantity has gone by several names through the years: hump factor, surface burn rate error (SBRE), and residual error to name a few. Since the scale factor forces the average burning rate to match that in the test, the net integration of the BARF curve should have no effect on burning time. For most motors, the result takes on a hump-shaped appearance with maximum errors in burning rate usually being between 2-10%. Burning rate errors of this magnitude translate to errors in pressure of 3-15% due to the nonlinear dependence of pressure on this parameter. Errors introduced due to the present technique for predicting ballistic response can require grain redesign and additional static tests. In addition, initial uncertainties in the ballistic prediction of maximum chamber pressure impacts the design of motorcase, nozzle, and insulation components since these parts must be designed for "worst case" predictions. Even if initial tests are deemed to be adequate, thrust history variations from the optimal design can cause losses in payload capability. Finally, spatial burning rate variations not normally considered by the ballistician can lead to changes in insulation exposure times when compared with current prediction methodologies. This Note will investigate means to improve ballistic predictions by determining the contribution of spatially dependent burning rate variations to the BARF effect for a simple cylindrical-port motor. Background associated with research into BARF effects is provided in the next section, followed by a description of the technical approach. An analysis of a simple ballistic test motor follows this discussion, along with conclusions from the study. While propellant strain, grain deformations during pressurization, local gas velocity effects, and possible migration of propellant constituents have all been theorized to contribute to BARF effects, the primary influence appears to be attributable to spatial variations in the local burning rate within the propellant grain. We make this assumption because the "hump shaped" character of the curve seems to be consistent across many motors of varying grain geometry, case deformations, and propellant formulations. In nearly all cases, spatial burning rate variations are attributed to one of two effects resulting from the rheological processes undertaken in loading

In recent years, substantial improvements in the performance of solid propellant guns have resulted from the development of higher energy propellants, higher loading density propellant charge configurations, and propellant geometries and concepts that have provided the progressively increasing gas generation rates required to efficiently use available increases in total energy. Unfortunately, these same features also typically lead to increases in ammunition vulnerability to enemy threats. Coupled with the current interest in much lighter fighting vehicles, the need for ammunition with reduced rather than increased sensitivity is obvious. This report describes the development of a new approach in the U.S. Army to address propellant energy/ performance and sensitivity/vulnerability as a single set of critical design requirements, to be addressed concurrently from the very beginning of the new energetic material research and development cycle. Some elements of this work were presented in abbreviated form at the 19th International Symposium on Ballistics in Interlaken, Switzerland in May 2001.

An aerodynamic analysis of a pneumatic launch system capable of accelerating a 300 metric ton vehicle to 268 m/sec (600 mph) is presented. Vehicle acceleration is constrained to be less than or equal to 3-g (29.43 m/sec ). The launch system is a horizontal pneumatic ram (catapult) configuration. The ram is modeled as a cylindrical piston within a tube. Compressed air is injected at the upstream head end of the tube and the piston accelerated. The vehicle is attached to the ram and is accelerated with it. Injected air mass flow and total pressure are varied over time. The interior ballistics problem, fore and aft of the ram, is solved by using an unsteady, onedimensional method of characteristics technique. A genetic algorithm is used to find the optimum mass flow and total pressure vs. time at the injector, expressed as polynomials. A parametric study is then conducted on the performance of the system using the optimized polynomials. The results of the parametric study are compared to results obtained from a quasi-steady, Fanno flow model and to data obtained from a lab-scale model. Introduction The Highly Reusable Space Transportation (HRST) program was set up to to study concepts that would significantly lower launch costs. Part of this program includes the development of a ground-based launch system capable of providing first stage acceleration to the launch vehicle, resulting in a fuel mass reduction or a possible payload mass increase. A pneumatic launch system could offer a relatively simple and robust alternative to electromagnetic systems. The proposed system is a pneumatic ram consisting of a cylindrical piston in a circular tube, similar to the Navy's catapult launchers on aircraft carriers. The tube is assumed to be 7.92 m (26 ft.) in diameter and 1225 m (4019 ft.) in length. The length constraint comes from the kinematics of the ideal case of a constant 3-g acceleration (space shuttle maximum). The diameter constraint is more arbitrary but is representative of today's tunneling capabilities. Compressed air enters through a single injector at the base of the launch tube. The vehicle mass is assumed to be 300 metric tons. The piston mass is considered to be small in comparison to the vehicle mass and is neglected. 'Graduate Research Assistant, Aerospace Engineering; now Engineer/Scientist, Boeing 'Associate Professor, Aerospace Engineering; Senior Member AIAA * Director, Space Power Institute & Professor, Electrical Engineering Copyright © 1998 by the American Institute of Aeronautics and Astronautics, Inc. AH rights reserved. V«Mcl«

Thefundamentalsoftheinternalballisticsofsolid-propellantnozzlelessrocketmotorshavebeenstudiedtheoreticallyandexperimentally.Aimedatthemajorbasicaspects,thetheoreticalanalysisconsistedofaquasi-steady-state one-dimensionale ow ofa perfect gas in a constant-area port, assuming a uniform burning rate along the grain asa resultofthecompensating effectsoferosiveand pressure-dependentburning contributions.Thesimplie edanalysis has beenfound to be an excellent tool to exhibit fundamental characteristics. Itrevealed that thetheoreticalachievable specie c impulse in a nozzleless rocket cannot exceed approximately 86% of its value in an adapted-nozzle rocket operating at the same average chamber pressure. An experimental parametric study using cylindrical propellant grains has demonstrated good agreement with the major parameters addressed in the theoretical analysis, indicating that the assumption of a uniform burning rate is a realistic approximation.

LTV Aerospace and Defense Company (LTVAD) using the company's highly reliable, reusable electromagnetic (EM) railguns have conducted over 200 projectile launchings since the second Electromagnetic Launch Technology Symposium and have established a projectile/launcher data base covering interior as well as exterior ballistic considerations. Projectiles weighing 2 to 43 grams have been launched with the LTVAD EM launcher lab's 12.7 and 20 mm railguns over the velocity range of 1.5 to 8.5 km/sec. This paper describes the interface and compatibility relationship between an EM launcher and the launch package during the interior ballistics of launch and the influence on the subsequent exterior ballistics. Some terminal effects and test descriptions conducted at LTVAD are presented along with associated projectile monitoring instrumentation utilized in determining projectile motion, integrity, orientation, flight characteristics, and impact phenomenology. This work was sponsored by the Army Ballistic Missile Advanced Technology Center.

The concept of a nozzleless solid-propellant booster for an integral-rock et-ramjet missile system offers a number of advantages over the conventional ejectable-nozzle design. These advantages include elimination of the debris hazard, simplicity of design, reliability, and performance. Experience with both subscale and full- scale motor designs shows that with a grain length to diameter ratio of 3.5, a nozzleless booster will match the performance of an ejectable-nozzle system, and that at larger ratios the nozzleless motor can be configured to produce up to 15% greater performance. General design rules and limitations are also presented. URING the last six years, our organization has been funded to perform a number of model studies and test programs aimed at developing nozzleless boosters for in- tegral-rocket-ramjet systems. This work has been performed with the goal of characterizin g the behavior and comparing the performance of various nozzleless booster configurations. The motor programs and analytical studies span the full range of tactical and strategic air launched systems and include the use of reduced smoke, aluminized, and high-density zir- conium-loaded propellant formulations. In the implementation of these programs, over 250 noz- zleless rocket motors, many of them containing integral- rocket-ramjet-nozzle inserts, having been functionally tested. Boosters ranging in size from 3.5 to 20.0 in. in diameter have been fired to provide a data base for the evaluation and modification of the nozzleless internal ballistics code that is used as the primary design tool for new system applications. A sufficient number of combinations of propellant systems and motor configurations have been tested so that there are enough empirical data to allow extrapolation with assurance that the accuracy of tht ballistics predicted by the model will fall within 0.5-2.5%. Therefore, the data presented are based on a model that is not as precise as the available nozzled ballistics program, which are generally twice as accurate as the current nozzleless program. This difference is due primarily to the relative complexity of the phenomena that control the behavior of a nozzleless motor and partly to the fact that nozzleless technology is a relatively new field. Work on a second-generation prediction model, which will be more theoretically based and much less dependent on empirical constants, has begun and will be completed next year. Background The concept of a nozzleless solid-propellant rocket motor was revived about 10 years ago in an attempt to produce a simpler and therefore more-economical rocket motor. It was then anticipated that the elimination of the nozzle assembly, the reduction of case insulation requirements, and the relative simplicity of the grain configuration would lead to a net production-cost saving on the order of 10-20%. Initial experimental data showed that, for a given external motor geometry, the lower operating efficiency of the noz

A program was initiated to design, build and evaluate the performance of a two-stage light gas gun, utilizing hydrogen gas, for use as an injector to an electromagnetic railgun. This effort is part of a project to develop a hypervelocity electromagnetic launcher for equation-of-state studies (HELEOS). The specific design features that enhance compatibility of the injector with the railgun, including a slip-joint between the injector launch tube and the coupling to the railgun, are described. The operational capabilites for using all major projectile velocity measuring techniques, such as in-bore pressure gauges, laser and CW (continuous wave) X-ray interrupt techniques, flash X-ray, and continuous in-bore velocity measurements using VISAR interferometry, are discussed. An internal ballistics code for optimizing gun performance has been utilized to interpret performance data of the gun. >

This paper demonstrates the ability of the Saderholm erosive burning model, when coupled with the Air Force Rocket Propulsion Laboratory Nozzleless Rocket Motor Internal Ballistics Computer Program, to predict the ballistic performance of six nozzleless rocket motors of three designs loaded with three nonaluminized HTPB propellants. The paper describes the Saderholm erosive burning model, the six nozzleless test motors, and the ballistics prediction methodology. The results for instantaneous and total ballistic parameters show that the Saderholm erosive burning model as developed for nozzled rocket motors predicts the ballistic performance of nozzleless rocket motors as well as or better than the Erosive Model 1 developed specifically for nozzleless rocket motors and built into the AFRPL computer program.

Analytical studies show that the effect of low-level wind on rocket trajectory dispersion is reduced by judicious shaping of the rocket's thrust-time curve. The dispersion is reduced by a periodic thrust which is initially large and oscillates for a few cycles. When the horizontal wind is constant, the phase of the oscillations depends only on the rocket aerodynamic pitching frequency and not wind magnitude or direction (provided linear aerodynamics is not violated). A series of six-degree-of-freedom trajectory simulations of the ARC AS® sounding rocket confirms that the predicted dispersion reduction does occur. The reduction for singlestage, solid-propellant rockets, however, seems to be limited by the state-of-the-art of internal ballistics. The possibility of winds being highly variable suggests that a single initial high-low thrust variation may be a reasonable design goal. For larger vehicles with strap-on boosters, the duration of the high-thrust boost should not exceed the time required to execute about one-quarter of the first pitching oscillation.

High loading densities and flexible thrust-time histories can be obtained in solid-propellant rocket motors by incorporating circumferential slots into a cylindrically perforated grain (slotted-tube motors). However, the head-end pressure of such motors can depart markedly from predictions by conventional methods. The departures are characterized by abnormally high head-end pressures at ignition; propellant fracture and case rupture have occurred. Analysis of test data and water table investigations have indicated that these effects are caused by aerodynamic interactions between the axial port flow and radial slot flows coupled with propellant deformation near the slots. An analytical model of the aerodynamic interaction region was constructed, and a graphical technique was developed to account for coupling effects so that the motor operating point could be denned. Design modifications based on the analysis and test results that minimize slot effects are discussed. Peak head-end pressures during ignition of the Castor II motor were predicted to be somewhat higher than test results.

the spatial distribution of particle mass. Assumption of uniform number distribution gives an over-estimation of particle damping. For noncircular cylindrical rocket chambers, steady state internal ballistics must be considered to determine the particle distribution. Particle size growth should in general have a stabilizing effect. Quantitative prediction must await better knowledge of how particles grow within the combustion chamber.

The ignition transients and penetrative burning characteristics of confined granular propellant beds in a cylindrical tube (loading densities up to 1.03 g cm3 and pressures up to 4000 bar) were investigated to test the 1-D pressure-wave propagation profiles predicted by the 1971 Kuo-Vichnevetsky-Summerfield analytical model. Thus, it was found that following the initial pressure rise along the bed, the position of peak pressure occurs within the bed and progresses downstream at an accelerating rate. The ignition time of the granular bed increases sharply with decreasing loading density. Wall friction acting on the unburned propellant along the tube attenuates downstream transmission of solid phase pressure generated by the upstream burning processes. This work has applications to the internal ballistics of guns, deflagration to detonation transition, and fast-burning rocket charges.

The performance variations due to acceleration loads imposed on spinning solid propellant rocket motors are investigated. The four potentially most significant modes of acceleration-induced phenomena are identified from a study of the literature and modeled. The four modes are a mechanical mode which deals with deformations of the propellant and case: a thermodynamic mode which covers acceleration-induced combustion phenomena; a stress mode which covers the stressed propellant's effect on burn rate; and a gas dynamic mode which deals with changes in gas flow in the chamber and through the nozzle. Simplified models of each mode are developed or taken from the literature and are added to an internal ballistics evaluation computer program. The resulting analysis is the first to include all of the modes. In order to do this an original analysis of the mechanical and stress modes was necessary. However, the analysis shows that the stress mode is not important for the circular perforated grains studied. The other effects are shown to have a significant influence on solid rocket motor performance. The magnitude of the different mode effects are such that one may not be ignored over the others as has been done in the past. The results of the analysis are compared to published rocket motor data. The comparisons indicate an erosive burning effect that is a function of spin rate. A qualitative explanation of the erosive effect is presented.