Tae-Seong Roh

Application of Eulerian–Lagrangian Approach to Gas-Solid Flows in Interior Ballistics

In a gun system, polydisperse phenomenon may occur due to the local combustion by an igniter system during the firing process. The Eulerian–Eulerian approach still lacks the capability of describing particle mixing under given conditions. A detailed insight of the interior ballistics must be predicted for the better safety and the lower cost at the development stage. The multiphase particle in cell (MP-PIC) model based on the Eulerian–Lagrangian approach, known to be more efficient than the conventional Eulerian–Lagrangian approach, has been initially applied for the simulation of the interior ballistics. A good efficiency with the MP-PIC model has been obtained in terms of the computational cost. The axisymmetric numerical code with the MP-PIC model has been developed for two-dimensional analysis of the interior ballistics. As part of the verification process for the code, several test computations have been performed: sod shock tube, free piston motion problem, and virtual gun calculated by IBHVG2 code. The code has become reliable with well-agreed results with the comparison data. Additionally, a numerical model for the orifices to describe the vent holes of the igniter on the coarse grid has been developed with the lumped parameter method used in the IBHVG2. Based on the model, the pressure behavior in the gun chamber according to the igniter length has been investigated. The computational results have shown that the negative differential pressure occurs clearly when the igniter is sufficiently short.

Numerical Study on Properties of Interior Ballistics According to Solid Propellant Position in Chamber

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

Derating design for optimizing reliability and cost with an application to liquid rocket engines

Abstract Derating is the operation of an item at a stress that is lower than its rated design value. Previous research has indicated that reliability can be increased from operational derating. In order to derate an item in field operation, however, an engineer must rate the design of the item at a stress level higher than the operational stress level, which increases the item׳s nominal failure rate and development costs. At present, there is no model available to quantify the cost and reliability that considers the design uprating as well as the operational derating. In this paper, we establish the reliability expression in terms of the derating level assuming that the nominal failure rate is constant with time for a fixed rated design value. The total development cost is expressed in terms of the rated design value and the number of tests necessary to demonstrate the reliability requirement. The properties of the optimal derating level are explained for maximizing the reliability or for minimizing the cost. As an example, the proposed model is applied to the design of liquid rocket engines.

Analysis of Elements Influencing on Performance of Interior Ballistics

The analysis of performance and internal flow according to various numerical models for interior ballistics has been conducted. The initial flow has been mainly affected by the drag model of propellants and their drag degradation reduces oscillations of differential pressure between the breech and the shot base. Models of Nusselt number haven`t influenced the major performance of interior ballistics. The negative differential pressure isn`t generated in the case without the heat transfer of propellants.

Development of Numerical Model for Igniter and Study on Initial Ignition of Interior Ballistics

ABSTRACT A numerical model of the igniter for the interior ballistics has been developed by combining lumped parameter model with the theoretical equation of orifice. With the developed model of the igniter, the numerical study on characteristics of the interior ballistics h as been conducted according to the igniter configuration in terms of igniter length, side hole diameter, a nd distribution of side holes. As results of the calculation of the pressure difference between the breec h and shot base, the low-cycle oscillations have been influenced by the igniter length, while the high-cycle oscillations have been affected by the side hole diameter and the distribution of side holes.초 록 Lumped parameter model에 오리피스의 이론식을 결합하여 강내탄도의 점화기 해석 모델을 개발하였다. 이 개발된 점화기 해석 모델을 이용하여 점화기 형상인 길이, 직경, 주입구 분포에 따른 강내탄도의 특성을 분석하였다. 포미와 초기탄저의 압력차의 결과로서 점화기 길이는 저주기 진동에 영향을 미치는 것으로 나타났고, 점화제 주입구 직경과 주입구 분포는 고주기 진동에 영향을 주는 것으로 나타났다.Key Words: Interior Ballistics(강내탄도), Two-phase Flow(이상유동), Gas-Solid Flow(기체-고체 유동), Igniter(점화기)

Design Optimization of Liquid Rocket Engine Using Genetic Algorithms

ABSTRACT A genetic algorithm (GA) has been employed to optimize the major design variables of the liquid rocket engine. Pressure of the main combustion chamber, nozzle expansion ratio and O/F ratio have been selected as design variables. The target engine has the open gas generator cycle using the LO2/RP-1 propellant. The gas properties of the combustion chamb er have been obtained from CEA2 and the mass has been estimated using reference data. The objective function has been set as multi-objective function with the specific impulse and thrust t o weight ratio using the weight method. The result shows about 4% improvement of the specific impulse a nd 23% increase of the thrust to weight ratio. The Pareto frontier line has been also obtained f or various thrust requirements.초 록 유전알고리즘을 사용하여 액체로켓엔진의 연소실 압력과 노즐 확장비, O/F 비 등 주요 설계변수를 최적화하였다. 대상엔진은 LO2/RP-1을 추진제로 사용하는 개방형 가스발생기 사이클을 대상으로 하였다. 연소실의 물성치는 CEA2를 이용하였으며, 무게 산출은 참고문헌을 바탕으로 모델링 하였다. 최적설계의 목적함수는 비추력과 추력중량비를 다중목표로 설정하여 가중치 방법을 사용하였다. 유전알고리즘을 최적화 과정을 거친 결과 비추력은 최대 4%, 추력중량비는 최대 23% 정도 증가하였다. 또한 다양한 추력에 대해서 Pareto frontier line을 얻었다.Key Words: Liquid Rocket Engine(액체로켓엔진), Design Optimization(최적설계), Genetic Algorithm(유전 알고리즘)

Study on Properties of Interior Ballistics According to Ignition-Gas Injections

Using the numerical code for the interior ballistics, the performance of the interior ballistics with the characteristic of the ignition-gas injections has been investigated. The ignition gas has been assumed to be injected into the chamber with 3 cases. As the results of analysis, when the ignition-gas has been injected into all chamber area, the pressure distributions of the chamber of the interior ballistics have been uniform and the differential pressure has been stable. The ignition-gas has been injected into the partial area of the chamber, however, the pressure distributions and the differential pressure have been unstable. The case using the longer ignition injector, therefore, seems to be more suitable to improve the stability of the interior ballistics.

Study on the Propellant Position for the Decrease of the Differential Pressure in the Interior Ballistics of a Gun Propulsion System

․ Dong-Whan Choi***ABSTRACT The position effect of the solid propellant in the combustion chamber on the decrease of the differential pressure has been investigated using the IBcode. Generally the metallic cartridge or CCC (combustible cartridge case) are used to load the propellant of the gun propulsion system. The position of the cartridge(propellant) is, therefore, a major factor for the interior ballistics in case the combustion chamber is larger than the cartridge. In this study, three different positions in the empty space of the chamber have been considered. As results, the case of the propellant located in the region near the base and breech has shown that the negative dif ferential pressure and the difference between the breech pressure and the base pressure are much higher than those of the case of the propellant located in the center of the chamber. The case of the propellant in the center of the chamber is, therefore, more profitable to improve the performan ce of the interior ballistics.초 록 IBcode를 사용하여 강내 차압감소를 위한 추진제 위치 연구를 수행하였다. 보통 화포의 추진제는 금속재질의 탄피나 소진탄피에 장전된다. 따라서 약실이 탄피보다 크다면 탄피(추진제)의 위치가 강내탄도 성능의 주요 인자가 된다. 본 연구에서는 약실 내 빈 공간이 발생하였을 경우를 고려하여 연구를 수행하였다. 약실 내 추진제 위치를 3가지로 변형하여 연구를 수행하였고, 추진제가 포미(Breech)나 탄저(Base)에 위치하였을 경우 마이너스 차압이 발생하였으며 포미 압력과 탄저 압력의 차가 추진제를 약실 가운데에 위치하였을 경우에 비해 증가함을 확인했다. 따라서 약실 가운데에 추진제를 위치시키는 것이 강내탄도 성능 향상에 유리하다는 결론을 내릴 수 있었다.Key Words: Interior Ballistics(강내탄도), Propellant Position(추진제 위치), NDP(Negative Differential Pressure)(마이너스 차압)

Performance Analysis of Interior Ballistics using 1-D Numerical Method

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

A Study on Diagnostics of Single Performance Deterioration of Aircraft Gas-Turbine Engine Using Genetic Algorithms

Genetic Algorithms(GA) which searches optimum solution using natural selection and the law of heredity has been applied to learning algorithms in order to estimate performance deterioration of the aircraft gas turbine engine. The compressor, gas generator turbine and power turbine are considered for engine performance deterioration and estimation for performance deterioration of a single component at design point was conducted. As a result of that, defect diagnostics has been conducted. The input criteria for the genetic algorithm to guarantee the high stability and reliability was discussed as increasing learning data sets. As a result, the accuracy of defect estimation and diagnostics were verified with its RMS error within 3%.