A computational approach capable of modeling homogeneous condensation in nonequilibrium environments is presented. The approach is based on the direct simulation Monte Carlo (DSMC) method, extended as appropriate to include the most important processes of cluster nucleation and evolution at the microscopic level. The approach uses a recombination-reaction energy-dependent mechanism of the DSMC method for the characterization of dimer formation, and the RRK model for the cluster evaporation. Three-step testing and validation of the model is conducted by (i) comparison of clusterization rates in an equilibrium heat bath with theoretical predictions for argon and water vapor and adjustment of the model parameters, (ii) comparison of the nonequilibrium argon cluster size distributions with experimental data, and (iii) comparison of the nonequilibrium water cluster size distributions with experimental measurements. Reasonable agreement was observed for all three parts of the validation.
Rapid prototyping techniques, materials, and apparatus have evolved to the point that they can be considered for the fabrication of hybrid rocket motor fuel grains. The Aerospace Corporation has initiated a test program to investigate the potential benefits to hybrid motor performance from the complex motor grain shapes enabled by these manufacturing techniques. Stereolithography has been used to produce several small proof-of-concept motors, each having complex 3-dimensional oxidizer flow passages that could not be produced using conventional hybrid manufacturing techniques. A new small hybrid motor test stand has been developed to explore the potential benefits that these techniques may offer. Preliminary results indicate that several of the problems that limit the use of hybrid rocket motors might be alleviated by the design freedom afforded by these new fabrication capabilities. I. IntroductionAPID Prototyping (RP), often called Additive Manufacturing (AM), is a family of technologies used to generate 3-dimensional shapes by computer control. Several diverse technologies fall under this broad term. In the typical Rapid Prototyping process, thin 2-dimensional layers of material are laid down, one on top of the other to form 3-dimensional shapes. A wide range of materials from plastics to foodstuffs can be literally printed in three dimensions. 1 The obvious benefits of RP techniques apply to a great many fields and products. These include the elimination of expensive tooling, decreased design cycle-time, and the de-coupling of design complexity from fabrication cost. 1 Additionally, RP offers some advantages that are more subtle and more profound for the specific applications of hybrid and composite solid rocket motor fabrication. Many RP processes deposit organic materials and can be employed to directly produce fuel grains. These grains, free from the constraints of physical tooling, may incorporate shapes and features that increase mixing and surface area or help balance the oxidizer-to-fuel ratio over the course of a burn. Another benefit of RP is that structural, plumbing, ignition, propellant management, and even diagnostic features can be "written" directly into the fuel grain design and then fabricated as a monolithic part. 2 The current disadvantages of rapid prototyping, as applied to fuel grain fabrication, are a paucity of appropriate fuel materials, slow fabrication speed, size limitations, and a lack of flight heritage. Also, most providers of RP fabrication machines and materials show little interest in working with unusual additives that could potentially increase regression rate or specific impulse . Many of these problems will naturally be alleviated as the use of this rapidly evolving set of technologies continues to expand.Hybrid rocket motors suffer from several performance and reliability problems that might be alleviated by taking advantage of the design freedoms afforded by fabrication techniques that are not limited by physical tooling such as molds, mandrels, and dies. Candidates for ...
A computational approach to homogeneous nucleation is proposed based on Eulerian description of the gas phase expansion coupled with a Lagrangian approach to the cluster formation. A continuum, Euler/Navier-Stokes solver versatile advection code is used to model the gas transport, and a kinetic particle solver is developed in this work to simulate cluster nucleation and growth. Parameters in the new model were adjusted so as to match the known theoretical dimer formation equilibrium constants for the two gases under consideration, argon and water. Reasonable agreement between computed and available experimental data was found in terminal cluster size distributions for nozzle water expansions in a wide range of stagnation pressures. The proposed approach was found to be orders of magnitude faster than a comparable approach based on the direct simulation Monte Carlo method.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.