반응표면법을 적용한 소형민수헬기 연료 무게중심 계산모델 연구

박진섭 경상대학교 항공우주특성화대학원 2020 국내석사

IR 신호 저감을 위한 축소엔진의 노즐 형상별 열유동장 전산해석

이현진 경상대학교 항공우주특성화대학원 2018 국내석사

Reduction of the IR signal concerning susceptibility is very important for improving aircraft survivability. Since the IR signal is proportional to the temperature, the temperature field of the exhaust plume was analyzed by applying the aspect ratio to the nozzle exit of some of the techniques of IR reduction. At the same time, design nozzles were produced with the same size and compared with the temperature ejected in the experiment of the engine. As a result of comparison with engine experiments, the temperature difference and temperature distribution differed somewhat for each nozzle shape, but the overall tendency was confirmed to be consistent.

Development of a 3D discontinuous Galerkin method for the second-order Boltzmann-Curtiss based hydrodynamic models of diatomic and polyatomic gases

사티비르 싱 경상대학교 대학원 2018 국내박사

기존의 이원자 및 다원자 기체에 관한 접근 방식은 단일원자 기체와 기본적으로 동일한 것으로 알려져 왔다. 즉, 비열비가 수정된 보존(질량, 운동량, 에너지) 물리 법칙에 기초하고 있으며, 1차 정확도 구성 법칙과 함께 Bulk 점성을 무시하는 Stokes 가정에 근거하여 2 세기 전(1845년)에 유도된 이른바 Navier-Stokes-Fourier (NSF) 식을 그 근간으로 한다. Stokes 가정은 아르곤과 같은 단일원자 기체의 경우는 확실히 정당화되지만. 국소 열 평형과 거리가 먼 비단일원자 기체 (질소, 또는 공기, 이산화탄소)에는 그렇지 않다. 따라서 이원자와 다원자 기체 흐름의 열 비평형 효과에 대한 연구는 매우 중요하다. 본 연구에서는 이원자와 다원자 기체를 설명하는 적절한 마스터 운동 방정식을 연구하고 이에 기초한 수학적 지배 방정식에 관한 전산기법을 개발하는 것이다. 첫째, Generalized Hydrodynamics와 Balanced Closure 이론을 기반으로 이원자 및 선형 다 원자 기체에 관한 2차 정확도 구성 법칙을 Boltzmann-Curtiss운동 방정식으로부터 유도한다. 위상 공간에서의 비선형 결합 구성 관계식에 관한 Topology를 압축, 팽창 및 속도 전단류와 같은 기본 흐름의 경우에 대해 분석한다. 다음으로 다원자 기체의 회전 비평 형 효과를 강조하기 위해 다원자 기체의 중요한 두 가지 비평형 현상(충격파 내부 구조와 와류 내부의 속도 전단) 사이의 강한 상호 작용을 이론 및 전산계산을 통해 분석한다. 또한 본 연구에서는 먼저 1 차원과 2 차원의 Riemann 문제 해를 구하기 위해 Euler 시스템에 불연속 Galerkin (DG) 법을 적용하였다. 이 쌍곡선 시스템의 기본 구조 (접촉면, 불연속 충격파, 팽창파)를 수치적으로 연구하였다. 최신 DG 기법은 Euler 방정식을 푸는 데 성공했지만, Euler 방정식의 타당성은 평형 상태에 한정되므로 비평형 유동에는 유효하지 않다. 비평형 기체 유동을 분석하기 위해 1 차 NF와 2 차 Boltzmann-Curtiss 방정식을 풀기 위한 Mixed 기법 기반의 새로운 DG 기법을 개발하였다. 계산 모델의 정확도에 관한 최종 결정은 검증의 엄격한 검토를 통해 얻을 수 있다. 1 차 및 2 차 Boltzmann-Curtiss 모델을 다양한 문제에 적용한 다음 DSMC의 계산과 실험 결과와 비교하였다. DG 법을 정상 상태 및 비정상 상태의 천이 유동 문제, 보존법칙의 Smooth 및 Stiff 문제를 대해 검증하였다. 보존적, 비보수적인 변수의 검증 연구를 위해 충격파 구조에 대한 1 차 및 2 차 Boltzmann-Curtiss 모델의 해석 해를 고려하였다. 다양한 Limiter, 수치 Flux 함수, 경계 조건의 수치 구현 기법을 요약하였다. 또한 임의의 기하학적 형상에 적용이 가능한 삼차원 Maxwell 미끄럼 및 Smoluchowski 온도 점프 경계 조건을 개발하였다. 2 차 Boltzmann-Curtiss모델에 기초한 구성 관계식에서 나타나는 비선형 음함수 형태의 대수 방정식을 효율적인 계산하는 방법을 기술하였다. 1차 NF와 2차 Boltzmann-Curtiss 기반 Solver의 계산 비용을 직렬 및 병렬 컴퓨터 시스템에 대해 분석하였다. 2 차 Boltzmann-Curtiss 기반 Solver는 반복 수치기법에서 나타나는 반복 횟수가 유동 특성과 열적 비평형도에 따라 달라지기 때문에 계산 격자 수에 대해 비선형 거동을 나타내었다. 결론적으로 희박 및 마이크로 스케일 기체에 관한 2 차 정확도 Boltzmann-Curtiss모델 기반의 비선형 결합 구성 관계식에 대해 불연속 Galerkin 코드는 초 병렬 특성을 보여주었다. It is well known that in conventional approach, description of diatomic and polyatomic gases is basically the same as the monatomic gas; that is, it is based on the physical laws of conservation (mass, momentum, and energy), with the modified ratio of specific heats, and in conjunction with the first-order constitutive laws, the two-century-old so-called Navier-Stokes-Fourier equation based on a critical assumption made by Stokes in 1845 that the bulk viscosity vanishes. While the Stokes’s hypothesis is certainly legitimate in the case of monatomic gases like argon, there is ever increasing evidence that now indicates that this is not the case for non-monatomic gases—like nitrogen (or air) and carbon dioxide—that are far from local thermal equilibrium. Therefore, the study of thermal non-equilibrium effects of diatomic and polyatomic gas flow is extremely important. The general interest of the present study is to explore the suitable and proper master kinetic equations for describing diatomic and polyatomic gases and to develop computational methods to solve these kinetic equations. First, on the basis of Eu’s generalized hydrodynamics and Myong’s balanced closure, the second-order constitutive laws are derived from the Boltzmann-Curtiss kinetic equation for diatomic (and linear polyatomic) molecules. Then the topology of the second-order nonlinear coupled constitutive relations in phase space is investigated for elementary flow situations like compression, expansion, and velocity shear. Lastly, a theoretical and computational attempt is made to highlight the rotational non-equilibrium effects in polyatomic gases by investigating the strong interaction of two important non-equilibrium phenomena in polyatomic gases –compressive shock structure and velocity-shear of the vortex—using the second-order constitutive laws. In this study, discontinuous Galerkin (DG) methods were first employed for solving the Euler system in order to obtain the solution of the one- and two-dimensional Riemann problems. The basic structure of this hyperbolic system, such as contact discontinuity, shock wave, and rarefaction wave, were studied numerically. Although modern DG method has been successfully applied for solving the Euler equation, the validity of the Euler equation is restricted to an equilibrium state, and it is not valid for non-equilibrium flows. In order to investigate non-equilibrium gas flows, a new set of DG methods based on mixed DG-framework is developed for solving the first-order Navier-Fourier and second-order Boltzmann-Curtiss based equations. The final judgment on the accuracy of the computational models is obtained through a rigorous study of verification and validation. The first-order and second-order Boltzmann-Curtiss based models are compared with the solution of DSMC and experiments by considering various problems. DG methods are comprehensively verified and validated for steady-state and unsteady transient flow problems as well as smooth and stiff solutions of the conservation laws. The analytical solutions of first-order and second-order Boltzmann-Curtiss based model in the shock wave structure are considered as a verification study on conservative, primitive and non-conservative variables. A self-contained summary of numerical implementation of various limiters, numerical flux functions, and boundary conditions is provided for the pedagogical purpose. Also, the three-dimensional Maxwell velocity slip and Smoluchowski temperature jump boundary conditions are provided for arbitrary geometries. Efficient numerical methods for solving non-linear implicit algebraic equations arising from the second-order Boltzmann-Curtiss based constitutive relations are described, and the solutions of the constitutive relations are analyzed in detail. The computational cost of the first-order Navier-Fourier and second-order Boltzmann-Curtiss based solvers is investigated in the serial and parallel frameworks. It was shown that the computational cost of the second-order Boltzmann-Curtiss based solver behaves nonlinearly concerning the number of elements, due to the dependence of the number of iterations of the second-order Boltzmann-Curtiss based solver on the flow structure and the degree of thermal non-equilibrium. Finally, a super-parallel performance of a mixed explicit discontinuous Galerkin method was reported for the second-order Boltzmann-Curtiss based nonlinear coupled constitutive models of rarefied and microscale gases.

유도 비행체의 공력 및 RCS 통합설계에 관한 연구

송동건 경상대학교 대학원 2018 국내석사

In the recently direction of shape design, shape design aims to perform multidisciplinary designs together with design parameters for each field in cooperation with related other fields. In this research, optimized shape design is performed by integrating aerodynamic characteristics and RCS calculation of guided aerial vehicle. The similar shape of taurus KEPD 350 cruise missile as the analysis target, ANSYS Fluent and FEKO S/W are used to calculate aerodynamic characteristics and RCS. Regarding the initial taurus similar shape, aerodynamic characteristics calculation using the Spalart-Allmaras turbulence model and RCS calculation applying the Physical Optics method, which is a high frequency approximate method, was performed. Design variables are set as factors that affect aerodynamic characteristics and RCS reduction. Since then, Optimization was done based on design variables. In optimized taurus missile, the lift coefficient and drag coefficient in the aerodynamic characteristics decreased by about 2.2%, 1.66%, but L/D ratio decreased only 0.4%. So, it is judged that the aerodynamic characteristics loss is little change as compared with the initial taurus missile, and the RCS reduction effect increases by 24%.

블레이드의 결빙과 파편 분리가 헬리콥터에 미치는 영향에 대한 연구

서석주 경상대학교 항공우주특성화대학원 2019 국내석사

With greatly expanded operations and increasingly broad range of tasks for modern helicopters, awareness of the hazards associated with in-flight icing has become important. Traditionally, researches are focused on the effects of in-flight icing on lift, drag, weight, and thrust; however, ice shedding becomes another key hazard of in-flight icing. In-flight ice shedding is extremely dangerous for helicopters, since, on one hand, the asymmetrical ice break-up and shedding could create extremely severe vibrations of the rotor blade, and, on the other hand, ice break-up from the main rotor may strike the fuselage and tail rotor, or worse, find its way into the engine. Hence, research on ice shedding is vital to the safety of helicopters. Currently available trajectory and impingement analyses may not accurately predict damage caused by ice shedding. Experience has shown that analyses have not matured yet to the level of accurately predicting the trajectories of ice shed from helicopter, such as from main blade, tail blade. In order to investigate the ice shedding risk of main rotor bil rotor blade was conservatively considered the most critical ice that shed and its impact with the areas of concern. In this study, the ice shedding analysis technique is examined and summarized in order to perform the ice shedding analysis with reference to the previous research examples and test results. By analyzing the influence of ice shedding in designing the ice protection system of blade through the acquisition of the ice shedding analysis technique with the rotor blades, it is possible to improve the safety related to in-flight icing and to help safe undertaking of the actual flight test.

항공기 운용환경을 고려한 연료탱크 산소농도 최적 저감 방안 연구

김해영 경상대학교 항공우주특성화대학원 2019 국내석사

This study aims at developing a NEA flow estimation method to secure the necessary technology for applying OBIGGS (On-Board Inert Gas Generating System) to aircraft. For this purpose, the change in oxygen concentration in the fuel tank according to the NEA flow rate and concentration supplied to the fuel tank of the aircraft is estimated and validated. First, based on the theory of perfect mixed assumption, the average oxygen concentration change inside the fuel tank was calculated. Tests for validation of the predicted results are carried out by considering the aircraft operating environment (altitude change). Then, a simplified fuel tank model was applied without implementing complicated fuel tanks such as actual aircraft.

2차원 희박기체 유동 예측을 위한 DG 기법 기반의 NCCR-CFD 코드 연구

백상태 경상대학교 대학원 2016 국내석사

The study of gas flow in rarefied condition has emerged as an interesting topic in recent years. Generally, the hybrid methods combining the molecular direct simulation Monte Carlo (DSMC) and continuum Navier-Stokes-Fourier (NSF) theory have been used for solving this type of problem. However, there are several unsolved issues in the hybrid methods like how to accurately identify the near-equilibrium sub-domains. In the present study, a discontinuous Galerkin (DG) finite element method for the nonlinear coupled constitutive relation (NCCR) of non-equilibrium gas flows is developed. The NCCR-DG method was then applied to study the two-dimensional rarefied hypersonic flow in various benchmark cases. The results indicate that the NCCR-DG code based on the unstructured mesh can solve continuum and rarefied gas flows in more efficient way compared to the hybrid methods.

대기 조건에 따른 낙하산 조명탄의 하강 운동 분석

장우영 경상대학교 항공우주특성화대학원 2017 국내석사

Dropping using a parachute, which is one of the methods of operating the flares that changes its mass with time, requires an accurate analysis of the dropping time in order to avoid damage to the ground. In this thesis, computational analysis is performed for accurate prediction of a parachute system including flares. In order to analyze the trajectory and falling time of the parachute system, the ordinary differential equations of descending motion are analyzed by applying the Runge-Kutta numerical analysis technique. To obtain the drag coefficient of the parachute and flare, which is the key input information for dynamic analysis, a computational fluid dynamics analysis based on the Navier-Stokes equations was performed. Finally, the descending behavior of the parachute system was analyzed by applying air disturbance models.

마이크로엔진 및 UCAV의 IR 신호 및 유동장 전산해석

안창환 경상대학교 대학원 2017 국내석사

The IR susceptibility of the propulsion system of an aircraft is significantly affected by nozzle shapes. To examine the effects of nozzle shapes, various nozzle shapes were first selected by considering a full-scale UCAV and its propulsion system. First, a nozzle for the micro engine was designed, The thermal flow field was analyzed then for exhaust nozzles with different aspect ratio and curvature. The IR signatures of the micro engine nozzle were calculated through the narrow-band model, on the basis of thermal flowfield data obtained through CFD analysis. Finally, in order to check the similarity of thermal flowfields and IR signature of the micro-scale model and the full-scale UCAV propulsion system, several non-dimensional parameters associated with temperature and optical property of plume were introduced. It was shown that, in spite of some differences in actual values of non-dimensional parameters, the scaling characteristics on spectral feature of IR signature and effects of aspect ratio and curvature of nozzle configuration remain similar in micro-scale and full-scale cases.

항공기 낙뢰 인증과 영향성에 관한 전산 시뮬레이션 연구

김종준 경상대학교 대학원 2017 국내석사

Environmental conditions like icing, sand, rain and thunder have a major impact on the life cycle and safety of the aircraft. Among them, lightning strike brings high level of current and voltage into the aircraft in very short time, generating high temperature and magnetic field. The high temperature can cause physical damage to the aircraft structure while the strong magnetic field can lead to the failure of electronic equipments. Thus lightning becomes a big threat to the safety of the aircraft. In this study, the principle of lightning strikes in the atmosphere, the mechanism of aircraft lightning strike, and the direct and indirect effects by lightning strike were investigated. Further, aircraft accidents, the condition imposed by certification authority, and the test standard provided by Aerospace Recommended Practice (ARP) were examined. On the basis of the ARP, computer simulation similar to the actual lightning strike event was also performed. Through electro-thermal analysis using ABAQUS code, direct lightning effects on lightning protection systems in aircraft fuel tanks and radomes were analyzed. In addition, using EMA3D code based on the Maxwell equation, current distribution and effectiveness of the lightning protection system were investigated