P. Barry Butler

Numerical Study of Cavitation in the Wake of a Hypervelocity Underwater Projectile

The focus of this study is on cavitation in the wake of a high-velocity underwater projectile. A physical model based on the Euler equations is presented in terms of two-phase mixture properties. Mathematical closure is achieved by providing equations of state for the possible thermodynamic states: compressible liquid, compressible two-phasemixture,andcompressiblepurevapor.Fortheoperatingconditionsstudiedhere,allstatesaresubcritical. Theproposedmodelissolvedusingahybridcomputationalschemedevelopedtoaccuratelyresolvepropertyproe les across discontinuities. The model is validated with several one-dimensional test cases that have known analytic solutions. For modeling the hypervelocity underwater projectile, the model is shown to compute unsteady shockwave development as well as the projectile-wake cavitation zone. The model is then used to conduct a parametric study on the affect of e ow and projectile properties on cavitation.

Analysis of deflagration to detonation transition in high-energy solid propellants

Abstract Increasing the nitramine content of solid rocket propellants increases the overall performance of the system as well as the sensitivity to detonation by shock initiation. Under certain circumstances Deflagration to Detonation Transition (DDT) can occur in granulated high-energy solid propellant. The work presented here represents an effort to model the DDT process. The emphasis is on the transient events prior to the detonation as well as the steady-state detonation conditions. A Method of Lines (MOL) computer solution technique is used to solve the system of partial differential equations describing one-dimensional, two-phase, reactive flow. The Chapman-Jouguet (CJ) properties, detonation run-up distance, and detonation velocity predicted by the computer code compare favorably with experimental data and the steady-state detonation predictions made using the TIGER chemical equilibrium computer code.

Modeling and numerical simulation of the internal thermochemistry of automotive airbag inflators

Abstract This paper provides a comprehensive description of the coupled thermochemical processes that occur during the firing of an automotive airbag inflator. A mathematical model is developed to simulate the transient, thermochemical events associated with ignition and combustion of a pyrotechnic automotive airbag gas-generator unit (inflator). The governing equations for the airbag inflator model are derived by expressing conservation conditions for mass and energy in the interior combustion chamber, filter/cooling screens, exterior plenum, and discharge tank. Following a brief description of the model development and physical assumptions made in the analysis, two series of test calculations are presented. The first series of calculations is for a baseline test case of a conventional pyrotechnic inflator system that is characteristic of a standard discharge tank validation experiment. Transient pressure and temperature profiles generated by the airbag inflator model are presented along with properties at the exit nozzles. A parametric study demonstrates the usefulness of airbag inflator simulations in assessing the sensitivity of airbag pressure curves to various design parameters such as propellant and hardware properties and hardware dimensions. The second series of calculations illustrates the influence of pre-pressurized inert gas on the performance of a pre-pressurized pyrotechnic inflator system. Performance of the inflators is measured in terms of pressure-time and temperature-time profiles in the inflator and discharge tank as well as pressure-time integrals at specified times after ignition. The pre-pressurized pyrotechnic inflator shows certain advantages over conventional pyrotechnic units, including significantly lower requirements for solid propellant mass, lower operating temperature, more uniform performance at hot and cold ambient conditions, and higher thermal efficiency. The chemical composition of the inert gas, pre-pressurized system is also shown to influence the working process of the inflator.

Equilibrium Analysis of Three Classes of Automotive Airbag Inflator Propellants

ABSTRACT In most vehicle airbag systems, the gaseous mixture which fills the airbag comes from rapid combustion of a condensed-phase propellant. An area of current interest in the development of airbag systems is the decomposition behavior of these condensed-phase propellants over a range of operating conditions. The purpose of this paper is to examine the performance of gas-generating propellants by comparing the theoretical combustion behavior of three condensed-phase propellants commonly used in the airbag industry. The propellants discussed in this paper are a sodium-azide (NaN3) propellant, a non-azide propellant containing azodicarbonamide (ADCA), and a double-base propellant (DB). The thermophysical properties investigated in this study include the flame temperature and chemical composition of the product gases, the number of gaseous moles produced per mass of condensed-phase propellant consumed, the condensed-phase (slag) production of each propellant, and the toxicity of gas-phase combustion prod...

Shock propagation and blast attenuation through aqueous foams

Abstract Experiments cited in this paper reveal that aqueous foams are good attenuators of blast waves and the resulting noise. A model is presented which describes the behavior of an explosively produced blast wave propagating through aqueous foam. The equation of state for an air/water mixture is developed with specific attention to details of liquid water compressibility. Solutions of the conservation equations in a spherically one-dimensional form were performed using a finite-difference wave propagation code. Results are presented that indicate the effect of the foam expansion ratio as well as the dimensionless foam depth on the blast attenuation. The (limited) comparison of decibel level attenuation between the model and the experiments shows good agreement.

Performance and CO Production of a Non-Azide Airbag Propellant in a Pre-Pressurized Gas Generator

Abstract This paper presents a numerical study of the transient operation of a pre-pressurized (augmented) airbag inflator. Augmented inflators dilute hot gaseous products of propellant combustion with ambient temperature, high-pressure stored gas before discharging the mixture into the airbag. The solid propellant selected for this study is a non-azide propellant composed of a mixture of azodicarbonirnide, potassium perchlorate, and cupric oxide, Predicted performance of the inflator is presented in terms of pressure, temperature and mass flow rate profiles in the inflator and discharge tank which is used to simulate an airbag. This work also predicts first-order estimates of gas-phase species exit concentrations and characteristic residence times in the inflator. Carbon monoxide. produced as a product of combustion from the high flame temperature propellant, is partially converted to COz as it flows from an internal combustionchamber to the pressurized plenum before being discharged into the airbag, Spe...

Analysis of particle dynamics and heat transfer in detonation thermal spraying systems

A computational study of pulsed detonation thermal spraying is conducted using an axisymmetric two-dimensional transient gaseous detonation model. The variations of the particle velocity and temperature at impact on the target surface with the particle initial loading location are analyzed for different conditions. The geometry of the system and the loading locations of the particulate phase are key parameters in pulsed detonation thermal spraying. Since the process is extremely transient and the gas phase experiences a wide range of transient stages all on a timescale of a millisecond, the particle characteristics are strongly dependent on the instantaneous location in the gas stream. One cycle of detonation thermal spraying occurs on a time scale on the order of a millisecond due to the high gas velocities associated with detonation. Thus, a precise control of the process variable parameters is required to have a successful detonation coating process.

Analysis of gas flow evolution and shock wave decay in detonation thermal spraying systems

The reactive Euler equations with variable gas properties are solved in both axisymmetric and plane two-dimensional flows to analyze the gas flow evolution, shock wave decay, and shock reflections in pulsed detonation thermal spraying (PDTS) systems. The gas phase governing equations are numerically solved using a high-resolution shock capturing numerical method. Expansion-compression waves are formed upon external gas expansion and persist for a long time (on the time scale of a PDTS cycle) with wide fluctuations in the gas velocity and temperature. The results show that the reflected shock wave from the substrate dies out extremely fast that micron-sized particles used in PDTS do not encounter these transients. The external shock wave decay is also analyzed for different reactive mixtures and flow geometries and is related to the truncation of the computational domain and the implementation of numerical boundary conditions at the open end boundaries.

A two-dimensional axisymmetric flow model for the analysis of pulsed detonation thermal spraying

A multicomponent, two-dimensional axisymmetric transient flow model with variable gas properties is developed to analyze the pulsed detonation thermal spraying process. A high-resolution shock-capturing numerical technique is used to solve the gas-phase governing equations. The choice of the computational grid resolution that ensures the proper analysis of the detonation front is first discussed. The analysis presented also shows the importance of the proper treatment of the open-end boundaries in terms of shock wave transmission through the boundaries as well as the effects this treatment can have on the particulate phase analysis. The variations of the particle velocity and temperature at impact on the target surface with the particle initial loading location are also discussed.

Analysis of a Pulsed Detonation Thermal Spray Applicator

Abstract Pulsed detonation thermal spray applicators are used to deposit particulate-based coatings on metal components. The coatings usually consist of a unique class of thermal spray materials that are widely employed in numerous industries to enhance the surface of metal components. This paper presents an analysis and numerical simulation of an open tube pulsed detonation thermal spray applicator. Calculations are made to determine the theoretical detonation states attainable for typical operating conditions and to track the particle trajectories as they traverse the barrel, eventually impacting the target workpiece. The present investigation focuses on the combustion of acetylene in oxygen, diluted with nitrogen. Key parameters studied are: nitrogen dilution percentage, oxygen-carbon ratio, barrel location of solid-particle axial injection, and size of the injected particles. Results are presented on the effect of these design parameters on several important quantities including: detonation speed, velocity of the detonation product gases, detonation pressure, detonation temperature, temperature and velocity profiles of the solid particle as it travels through the pulsed detonation thermal spray applicator, percentage melt history of the solid particles, and temperature, velocity, and percentage melt of the solid as it impacts the workpiece.