Coupling of Level Set and Volume of Fluid Methods for Simulations of Transient Internal Flow Field in Solid Rocket Motors

This study entails the analysis of the working performance of solid rocket motors (SRM), featuring the essential element of internal ballistic analysis. Therefore, the internal flow field under the condition of burning surface regression needs to be calculated. The boundary of the internal flow field of the SRM moves with the combustion of the propellant; therefore, it is necessary to accurately track the mobile interface to provide boundary conditions for the flow field calculation. The coupling of the level set method and the volume fraction method is utilized to track the burning surface, and the porous media model is used to divide the fluid and solid calculation domains. The interface between the two calculation domains is used to characterize the burning surface, and then, the area of the burning surface is obtained by solving the area of the interface. The calculation and analysis are carried out for SRM with tubular charge and star charge. The results verify that the calculation model can accurately calculate the transient internal flow field of SRM under the condition of burning surface regression.

New Design Method of Solid Propellant Grain Using Machine Learning

The correlation between solid propellant grain configuration and burning surface area profile is a complicated nonlinear problem. Nonlinear optimization has been adopted to design grain configurations that satisfied the objective area profiles. However, as conventional design methods are impractical, with limited performance, it is necessary to investigate alternatives. Useful information for grain design can be obtained by analyzing the aforementioned correlation. However, this aspect has not been studied owing to the requirement of large amounts of data and analysis techniques. In this study, machine learning was used to develop a new design method. The objective of machine learning was to train a model to classify classes of data. The database stores various sets of configuration variables and their classes. The proposed Gaussian kernel-based support vector machine model predicts the class of newly designed grains. The results verified that the model accurately predicted the class of the set of configuration variables and can be used to modify the set of configuration variables to satisfy the requirement. Thus, it was confirmed that machine learning is an appropriate approach to grain design; however, further research is needed to analyze its practicality.

SOME TEMPERATURE CHARACTERISTICS SUB-LAYER AEROSOL EXTINGUISHING OF ALCOHOLS

Problem Statement: Nowadays, the process of sublayer aerosol quenching has not been studied at all, and its basic parameters, such as changes in flame temperature, liquid surface layer, tank sides, and approximate time of alcohol quenching and quenching, are unknown. The purpose of the work is to determine the parameters of sublayer aerosol quenching - flame temperature, the surface layer of liquid, tank sides, and the impact on the efficiency of sublayer quenching of aerosols dispersion – as one of the main parameters characterizing the process of alcohol quenching. The scientific novelty of the work is that for the first time the parameters of sublayer aerosol quenching at different sizes of aerosol bubbles were determined and it was found that at smaller bubbles the surface layer temperature decreases to 15%, aerosol distribution on the liquid surface is more uniform and a heterogeneous system is formed, which contains both aerosol solid particles – K2CO3, KOH, KNSO3, NH4HCO3, gases – CO2, N2, H2O, alcohol vapors, and the alcohol itself in the vapor and liquid phases. The main results of the study: The paper describes the developed installation and methodology for determining the parameters of sublayer aerosol quenching at different stages of the aerosol release process. The values of the flame temperature reduction and its behavior when the aerosol enters the flame are established. The established values are plotted and it is determined that when the aerosol enters the flame, the flame temperature begins to decrease actively and in 40 seconds reaches about 600 degrees Celsium. It was also found that the flame turns orange, which indicates that the combustion zone is the thermal dissociation of potassium salts, the flame size decreases, which indicates a decrease in the amount of alcohol vapor entering the combustion zone. The rate of cooling the sides at the exit of the aerosol from different-sized holes was also determined and it was found that the amount of cooling of the tank side is slightly higher at smaller hole diameters with a more uniform distribution of the aerosol on the surface. The range of reduction of liquid and board temperatures for each of the alcohols is less than the boiling point by 30-40 degrees Celsium. The decrease in temperature occurs at approximately the same rate and slows down until the end of the aerosol release. Analysis of the experimental results showed that the action of fire-extinguishing aerosol when it comes to the surface leads to intensive alcohol cooling due to bubbling of the aerosol through the alcohol layer, with active mixing of alcohol layers and the rise of cold liquids to the surface. This phenomenon leads to further cooling of burning surface of the liquid, which can have a temperature of 60 degrees Celsium to 97 degrees Celsium, as well as the sides of the tank as a result of alcohol on them and its intense evaporation. The result is the establishment of the parameters of the sublayer aerosol quenching – the temperature of the liquid surface, the temperature of the sides of the tank, the rate of aerosol to the surface, and the flame temperature when the aerosol enters the combustion zone.

An Improved Modeling of Solid Propellant Fracturing to Produce Long Fractures in Wellbore Formations

Simultaneous ignition of an entire exposed surface required for accurate modeling of solid propellant fracturing process is difficult to achieve because wellbore fluids decrease flame spread rate and negatively impact burn propagation, and can extinguish portions of the burning propellant grain thereby resulting in slower pressure loading rates and insufficient energy for producing long fractures. A proposed system is that in which the propellant is protected from wellbore fluids by housing it in a vessel with a means for creating openings to allow combustion gases produced to flow into the wellbore. On this basis, a model was developed using mass and energy conservation laws, and applying a concept of choked flow in the openings to relate conditions in the wellbore to the vessel. The results of the peak pressure and pressure rise time obtained from the model for multiple-fracture regime agree well with the reported experimental results and thus establishing the validity of the model in predicting the wellbore pressure during solid propellant fracturing system. A star-shape burning surface is proposed for the propellant and calculations carried out proves it to be more effective as it provides more energy for producing long fractures essential for more flow of oil and gas from the reservoir into the wellbore than a conventional circular surface of the same burning area. The exterior angle of star-shape burning surface was found to be a function of the number of vertices of the star and it determines the progressive burning nature of the propellant.

NUMERICAL SIMULATION OF INTRA-CHAMBER PROCESSES IN A SOLID ROCKET MOTOR WITH ACCOUNT FOR BURNING SURFACE MOTION

The axisymmetric solid rocket motor (SRM) with an “umbrella” shape is considered in this paper. The numerical algorithm based on the inverse Lax-Wendroff procedure for a gas dynamic equation and on the level-set method for tracking the burning surface is overviewed for internal ballistics problems. Assuming that the propellant combustion proceeds in a quasi-stationary regime and a mass flow from the burning surface depends on the pressure raised to the power of parameter ν, the numerical computations of intra-chamber combustion product flows during the main-firing phase are carried out using the numerical algorithm developed for “umbrella”-shaped SRM at different parameter values. The approximation convergence of flow parameters in a case of the stationary propellant surface and average intra-chamber pressure for all the time of motor operation is examined. The numerical simulation results are obtained and analyzed for different “umbrella” inclination angles. Though the developed algorithm has been applied to the motors with a specific shape, it can also be used for propellant grains of different shapes and is easily extended to 3D models.

In-situ management of paddy stubble through microbial biodegradation

After the harvest of crop, the disposal of the rice stubbles remains a notable area of interest in all the growing areas of rice. The present review paper explores and highlights an effective strategy of decomposing the decomposers of the paddy stubble. Due to the increasing production of rice, there is an increase in rice crop residues and stubbles production. Conventional methods of management of paddy involve burning, surface retention, mulching, bailing, incorporation/amalgamation and direct removal. However, there are certain environmental challenges by using available agricultural implements. Thus, this current study demonstrates strategic management of the paddy crop residue for a sustainable environment. The developed eco-friendly methods will render new dimensions for the application of the post harvested residues. The review paper will be significant for sustainable management of the wastes of the paddy crop and hence strategic decomposition method, which will be beneficial for the society, farmers as well as the environment

Two-component propellant grain for rocket motor: Combustion analysis and geometric optimization

The present paper considers utilization of rocket motor propellant grains that consist of two propellants. The idea is to achieve approximately neutral burning using an outer surface inhibited cylindrical shape and complex contact surface between propellants. An existing propellant grain with complex geometry has been analytically modeled in terms of determination of evolution of corresponding burning surface areas. The analytical and experimental results? diagrams of this grain have been found to have a saw-tooth shape because of the segments that separate the two propellants, causing potential problems in the burning process during the relatively short active phase, showing an obvious need for further optimization. This has created an opportunity for development of improved propellant grain geometry and corresponding mathematical model for determination of main interior ballistic parameters. Comparison between calculation results based on both models and experimentally determined chamber pressure data shows very good agreement. Therefore, two-component propellant grains have significant application possibilities using the suggested modeling approaches.

Dependence of the fire retardant and fire extinguishing efficiency of compositions based on phosphates of bivalent and trivalent ammonium metals on their physicochemical properties

Purpose. The object of research were fire-retardant and fire-extinguishing agents based on ammonium phosphates of bivalent and trivalent metals used for the treatment of forest combustible materials (FCM), including wood and peat. The subject of the research was to determine the fire-retardant and fire-extinguishing effectiveness of these agents, depending on their physical and chemical properties determined by the conditions of synthesis. The aim was to establish common traits or difference in the mechanism of inhibition of combustion of FCM by metallophosphate systems of various chemical compositions, as well as to reveal the role of the processes occurring in the condensed phase under the influence of their thermal decomposition products. The main task was to study the physicochemical, thermal properties of fire-retardant and fire-extinguishing agents, as well as fire-protected samples of peat and other FCM in the temperature range on the burning surface of natural materials (200–500 °C). Methods. X-ray phase analysis, differential scanning calorimetry, chemical analysis. Findings. The factors determining the fire-retardant and fire-extinguishing efficiency of synthetic agents based on phosphates of bivalent and trivalent ammonium metals with controlled properties depending on the synthesis conditions with respect to FCM, wood and peat have been determined. A process has been established that has a dominant effect on stopping their combustion – inhibition of radical reactions in the gas phase by volatile nitrogen-containing products. At the same time, it was shown that when developing new fire-retardant and fire-extinguishing agents, it is necessary to take into account their properties such as the ability to form thermal insulating structures in the condensed phase. Application field of research. The results obtained in this work can be used to create new fire-retardant and fire-extinguishing synthetic compositions based on ammonium phosphates of bivalent and trivalent metals for the treatment of forest fuels.