Damped Bypass Valve의 내부 누설 유동 특성 전산 해석

이세욱(Seawook lee),김대현(Daehyun Kim),김상범(Sangbeon Kim),박상준(Sangjoon Park),조진수(Jinsoo Cho) 한국항공우주학회 2013 韓國航空宇宙學會誌 Vol.41 No.2

비행조종작동기 제어용 파일럿 밸브의 내부 유동 및 응답 특성을 분석하기 위해 유동의 수치 해석을 수행하였고 내부 누설 특성을 해석하였다. 온도 변화에 따른 누설을 고려한 밸브의 작동온도를 결정할 수 있는 영역을 제안 할 수 있었다. 미량의 작동유체가 누설 영역으로 유출된다는 것을 확인하였으나 누설 효과는 작동 온도에 따라 영향을 미치지 않는 것을 확인하였다. 압력 상승률이 온도가 하강할수록 높아지는 경향을 나타냈다. A numerical analysis for the internal flow was carried out in order to analyze the leakage flow characteristics inside the damped bypass valve. This research has found that the valve characteristics became stable at above a specific temperature. Very small amount of leakage flow was occurred. But there was no effect in temperature. The more temperature fell, the more maximum pressure rate was increased.

비선형 와류격자법을 이용한 작은 종횡비 날개의 고받음각 및 지면효과 후류 특성 분석

이세욱,Lee, Seawook 한국교통대학교 융복합기술연구소 2014 융ㆍ복합기술연구소 논문집 Vol.4 No.1

For the analysis of lifting surface at high angle of attack, a Nonlinear Vortex Lattice Method(NLVLM) was used. The NLVLM is intented to compute the interactions between lifting surfaces and separated vertical flow. The lifting surfaces are represented by a lattice of discrete vortex rings. And wakes are represented by families of non-lintersecting, semi-infinite vortex line segments. The image method also used to analyze the ground effect. It is found that vortex lines separated from lifting surfaces represent the separated flows successfully. Although the present method is applied for the rectangular wing and delta wing, extensions can be possible for the arbitrary lifting surfaces. The Present results show good agreement with experimental data.

Use of CFD Analyses to Predict Disk Friction Loss of Centrifugal Compressor Impellers

CHO, Leesang,LEE, Seawook,CHO, Jinsoo THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2012 Transactions of the Japan Society for Aeronautical Vol.55 No.3

<P>To improve the total efficiency of centrifugal compressors, it is necessary to reduce disk friction loss, which is expressed as the power loss. In this study, to reduce the disk friction loss due to the effect of axial clearance and surface roughness is analyzed and methods to reduce disk friction loss are proposed. The rotating reference frame technique using a commercial CFD tool (FLUENT) is used for steady-state analysis of the centrifugal compressor. Numerical results of the CFD analysis are compared with theoretical results using established experimental empirical equations. The disk friction loss of the impeller is decreased in line with increments in axial clearance until the axial clearance between the impeller disk and the casing is smaller than the boundary layer thickness. In addition, the disk friction loss of the impeller is increased in line with the increments in surface roughness in a similar pattern as that of existing experimental empirical formulas. The disk friction loss of the impeller is more affected by the surface roughness than the change of the axial clearance. To minimize disk friction loss on the centrifugal compressor impeller, the axial clearance and the theoretical boundary layer thickness should be designed to be the same. The design of the impeller requires careful consideration in order to optimize axial clearance and minimize surface roughness.</P>

Dynamic Moving Mesh 기법을 이용한 비행조종작동기 제어용 파일럿 밸브 내부 정상/비정상 캐비테이션 유동 해석

손갑식(Kapsik Son),이세욱(Seawook Lee),김대현(Daehyun Kim),김상범(Sangbeom Kim),박상준(Sangjoon Park),장기원(Kiwon Jang),조진수(Jinsoo Cho) 한국항공우주학회 2011 韓國航空宇宙學會誌 Vol.39 No.7

비행조종작동기 제어용 파일럿 밸브의 내부 유동 및 응답 특성을 분석하기 위해 캐비테이션 모델과 격자 이동 기법을 사용하여 정상/비정상 유동의 수치 해석을 수행하였다. 작동 온도와 시간에 따른 밸브 내부 유동을 분석한 결과, 일정 온도 이상에서 밸브 특성이 안정되는 현상을 발견하였고 캐비테이션이 밸브 성능에 미치는 영향성을 파악하였다. 밸브 내부 압력과 응답 특성을 분석하였으며 비정상 유동이 발달하여 정상 유동 특성과 일치하는 것을 확인하였다. A numerical analysis of steady/unsteady flow applying cavitation model and moving mesh method was carried out in order to analyze ￡low and response characteristics inside the pilot valve which controls the flight actuator system. The flow of the valve was assessed according to operation temperature and time. This research has found that valve characteristics became stable at above a specific temperature and the cavitation affected valve’s performance. Internal pressure and response characteristics of the valve were analyzed and flow characteristics of steady and developed unsteady ￡low were confirmed to be matched each other.

초소형 무인기 추진용 프로펠러의 전산해석 및 풍동시험

조이상(Leesang Cho),이세욱(Seawook Lee),조진수(Jinsoo Cho) 한국항공우주학회 2010 韓國航空宇宙學會誌 Vol.38 No.10

초소형 무인기 추진용 MH-75 프로펠러는 자유와 설계기법을 이용하여 설계변수인 허브팁 비, 비틀림각 분포, 최대 캠버의 위치와 크기 그리고 시위 길이를 변화시키며 설계 요구조건을 만족하도록 공력설계 되었다. MH-75 프로펠러는 주파수영역 패널법을 이용하여 설계요구조건을 만족시키고, 다양한 초소형 무인기에 적용이 가능하도록 정지추력 특성과 비행속도 및 회전수 변화에 따른 성능 특성을 예측하였다. 그리고 MH-75 프로펠러의 공력해석 결과를 검증하기 위해 프로펠러의 추력특성에 대한 풍동시험을 수행하였다. MH-75 프로펠러의 추력 성능은 설계요구조건을 만족하였으며, 저레이놀즈 수 영향을 고려하기 위한 2차원 익형 해석용 XFOIL 프로그램에 비해 3차원 효과를 고려하는 주파수영역 패널법을 이용하는 것이 비교적 풍동시험 결과와의 오차가 적음을 확인하였다. The MH-75 propeller for the MAV propulsion is designed using a free vortex design method which considers design parameters such as the hub-tip ratio, the twist angle distribution, the maximum camber location and the chord length of the propeller blade. Aerodynamic characteristics of the MH-75 propeller are predicted by changing the flight speed using the frequency domain panel method. And, the thrust characteristics of the MH-75 propeller are measured using the balance system of the subsonic wind tunnel for the validation of numerical results. The performance characteristics of the MH-75 propeller satisfied with design requirements. Numerical results of the MH-75, which are predicted by the frequency domain panel method, are more agree with experimental results compare with XFOIL.

수직이착륙 무인항공기용 엇회전식 덕티드팬의 팁간극 영향에 대한 연구

민준호(Junho Min),류민형(Minhyoung Ryu),이세욱(Seawook Lee),조진수(Jinsoo Cho) 한국항공우주학회 2013 韓國航空宇宙學會誌 Vol.41 No.7

제자리 비행하는 수직이착륙 무인항공기용 엇회전식 덕티드팬의 전ㆍ후방동익 팁간극이 덕티드팬에 미치는 영향을 파악하기 위해 전산해석을 수행하였다. κ-ω SST 난류 모델을 사용하여 엇회전식 덕티드팬의 전산해석을 수행하였으며, 기준형상에 대해 제자리 및 전진 비행 상태의 공력특성을 풍동시험을 통해 계측하여 전산해석 기법을 검증하였다. 엇회전식 덕티드팬에서 특정 동익의 팁간극이 증가하면 그 동익과 덕트의 추력계수는 감소하고, 다른 동익의 추력계수는 증가하는 경향을 확인하였다. 후방동익의 팁간극이 증가하면 덕티드팬 출구면의 평균 전압을 상승시켜 덕티드팬의 추력을 증가시켰다. The tip clearance effect on counter-rotating ducted fan of VTOL UAV in hovering condition, was investigate using computational analysis. The κ-ωSST turbulence model is employed in this study. The numerical results of baseline model are validated by wind tunnel test in hovering and forward conditions. It is observed that if tip clearance of one rotor in the counter-rotating ducted fan increase then the thrust coefficient of another rotor increases. In Addition to this, when the tip clearance of the rear rotor increases, the thrust of the ducted fan is improved due to increasing of average total pressure at exit plane.

Effects of Inlet Turbulence Conditions and Near-wall Treatment Methods on Heat Transfer Prediction over Gas Turbine Vanes

Bak, Jeong-Gyu,Cho, Jinsoo,Lee, Seawook,Kang, Young Seok The Korean Society for Aeronautical and Space Scie 2016 International Journal of Aeronautical and Space Sc Vol.17 No.1

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ${\omega}RSM$ turbulence model. Additionally, the RNG $k-{\varepsilon}$, SSG RSM, and $SST_+{\gamma}-Re_{\theta}$ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ${\omega}RSM$ results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The $SST_+{\gamma}-Re_{\theta}$ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

Effects of Inlet Turbulence Conditions and Near-wall Treatment Methods on Heat Transfer Prediction over Gas Turbine Vanes

Jeong-Gyu Bak,Jinsoo Cho,Seawook Lee,Young Seok Kang 한국항공우주학회 2016 International Journal of Aeronautical and Space Sc Vol.17 No.1

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ωRSM turbulence model. Additionally, the RNG k-ε, SSG RSM, and SST+γ-Reθ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ωRSM results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The SST+γ-Reθ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

가스터빈 노즐 베인의 열전달 예측을 위한 벽면처리법 비교연구

박정규(Jeonggyu Bak),김진욱(Jinuk Kim),이세욱(Seawook Lee),강영석(Youngseok Gang),조이상(Leesang Cho),조진수(Jinsoo Cho) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.7

난류모델에서 벽면처리법이 터빈 노즐 베인의 열전달 예측에 미치는 영향을 비교·분석하였다. 본 연구를 위해 NASA의 C3X 터빈 노즐 베인을 사용하였다. 벽함수 방법, 저레이놀즈수 방법, 천이모델을 사용하여 베인 표면에서의 압력 및 온도를 해석하였다. 해석 결과 터빈 노즐 베인의 중간 압력분포는 각 벽면처리법에 따른 차이 없이 실험값과 잘 일치하였다. 그러나 터빈 노즐 베인의 온도와 열전달 계수는 각 벽면처리법에 따라 큰 차이를 보였다. 전반적으로 저레이놀즈수 방법과 천이모델은 벽함수 방법에 비해 온도 및 열전달 계수 예측에 특별한 이점을 보이지 않았으며, 벽함수 방법을 적용한 레이놀즈응력 난류모델이 터빈 노즐 베인 표면의 온도 및 열전달 계수를 비교적 잘 예측하였다. The comparative analysis of near-wall treatment methods that affect the prediction of heat transfer over the gas turbine nozzle guide vane were presented. To achieve this objective, wall-function and low Reynolds number methods, and the transition model were applied and simulated using NASA´s C3X turbine vane. The predicted turbine vane surface pressure distribution data using the near-wall treatment methods were found to be in close agreement with experimental data. However, the predicted vane metal temperature and heat transfer coefficient displayed significant differences. Overall, the low Reynolds method and transition model did not offer specific advantages in the prediction of temperature and heat transfer than did the wall-function method. The Reynolds stress model used along with the wall-function method resulted in a relatively high accuracy of prediction of the vane metal temperature and heat transfer coefficient.

레이놀즈응력 난류모델을 이용한 가스터빈 베인의 복합열전달 해석

박정규(Jeong-Gyu Bak),김진욱(Jinuk Kim),이세욱(Seawook Lee),강영석(Young Seok Kang),조진수(Jinsoo Cho) 한국유체기계학회 2014 유체기계 연구개발 발표회 논문집 Vol.2014 No.11