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Seungsoo Jang,Jihyun Hwang,Sung-Ju Park,Won Namkung,Moohyun Cho,Hyeong-Seok Seo 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.8
When the thermionic electron gun of the klystron operates, the structure around the cathode is subjected to thermal deformation due to the high operating temperature of the cathode. A thermal deformation analysis of the existing electron gun with `cold' dimensions (dimension on fabrication) was done using the ANSYS code to get the `hot' dimensions of the electron gun on operation. After that, the optics of the emitted electron beam were simulated using two codes (EGUN and CST-PS) for the two cases of the `cold' dimension and the `hot' dimension. We compared the beam trajectories of the above two cases to investigate the change in the physical quantities, which would have a strong effect on the klystron performance due to the thermal deformation. The thermal deformation was found to cause a perveance change as large as 15%. The scalloping behavior was also investigated with an applied magnetic field for the two cases of cold and hot dimensions.
블레이드 형상 변화에 따른 마이크로 축류 수차의 유동특성 및 구조적 안전성 연구
장승수(Seungsoo Jang),제영완(Yeong Wan Je),김명우(Myung Woo Kim),김윤제(Youn-Jea Kim) 대한기계학회 2021 大韓機械學會論文集B Vol.45 No.7
본 연구에서는 유동해석을 통해 마이크로 축류 수차의 블레이드 형상 변화에 따른 유동특성을 연구하였다. 첫째, 평평한 블레이드 형상과 NACA 하이드로포일 형상을 적용한 모델을 비교하였는데, 후자가 더 우수한 성능을 나타내었다. 둘째, NACA 하이드로포일 모델의 두께에 대한 영향성을 고찰하였는데, 두께가 두꺼워질수록 출력 및 낙차가 증가하는 경향을 보였다. 이는 블레이드 압력면 앞전 부근의 역압력구배에 기인한다고 할 수 있다. 이후, NACA 하이드로포일 모델에 대하여 구조적 안전성을 검토하기 위해 단방향 유체-구조 연성해석을 수행하였다. 전단 변형 에너지설에 입각한 항복안전계수 및 수정 Goodman 식을 이용한 피로안전계수 계산 결과, 구조적으로 안전하며 무한수명을 가질 수 있음을 알 수 있었다. 한편, 고유량의 탈설계점에서는 안전계수가 감소하여 무한수명에 대한 위험성이 증가하였다. In this study, the flow characteristics of a micro axial turbine were studied via flow analysis according to the blade configurations. First, flat and NACA hydrofoils were compared, and the latter was observed to have better performance. Second, the effects of blade thickness of the NACA hydrofoil were evaluated, and the output power and head tended to increase as the blade thickness increased; this observation was related to the variations in the effects of the adverse pressure gradients in the vicinity of the pressure-side leading edge. Thereafter, a one-way fluid-structure interaction analysis was conducted to examine the structural safety of the NACA hydrofoil model. The calculations of the yield safety factor based on the distortion energy theory and fatigue safety factor using a modified Goodman equation show that the material is structurally safe and has an infinite lifespan. However, at the off-design points of the high flow rate, the risk of fatigue failure increases as the fatigue safety factor decreases.
Jang, Yujin,Huh, Jinbum,Lee, Namhun,Lee, Seungsoo,Park, Youngmin The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1
The RANS equations are widely used to analyze complex flows over aircraft. The equations require a turbulence model for turbulent flow analyses. A suitable turbulence must be selected for accurate predictions of aircraft aerodynamic characteristics. In this study, numerical analyses of three-dimensional aircraft are performed to compare the results of various turbulence models for the prediction of aircraft aerodynamic characteristics. A 3-D RANS solver, MSAPv, is used for the aerodynamic analysis. The four turbulence models compared are the Sparlart-Allmaras (SA) model, Coakley's $q-{\omega}$ model, Huang and Coakley's $k-{\varepsilon}$ model, and Menter's $k-{\omega}$ SST model. Four aircrafts are considered: an ARA-M100, DLR-F6 wing-body, DLR-F6 wing-body-nacelle-pylon from the second drag prediction workshop, and a high wing aircraft with nacelles. The CFD results are compared with experimental data and other published computational results. The details of separation patterns, shock positions, and $C_p$ distributions are discussed to find the characteristics of the turbulence models.