Jongjae Cho

An Experimental Study on the Flow Characteristics ofa Supersonic Turbine Cascade as Pressure Ratio

In this paper, a small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade by experiment. The flow was visualized by means of a single pass Schlieren system. The supersonic cascade with 3-dimensional supersonic nozzle was tested over a wide range of pressure ratio. Highly complicated flow patterns including shocks. nozzle-cascade interaction and shock boundary layer interactions were observed.

Optimal Design for the Rotor Overlap of a Supersonic Impulse Turbine to Improve the Performance

In a supersonic turbine, A rotor overlap technique reduced the chance of chocking in the rotor passage, and made the design pressure ratio satisfied. However, the technique also made additional losses, like a pumping loss, expansion loss, etc. Therefore, an approximate optimization technique was appled to find the optimal shape of overlap which maximizes the improvement of the turbine performance. The design variables were shape factors of a rotor overlap. An optimal design for rotor overlap reduces leakage mass flow rate at tip clearance by about 50% and increases about 4% of total-static efficiency compared with the base model. It was found that the most effective design variable is the tip overlap and that the hub overlap size is the lowest.

Improvement of the Aerothermal Environment for a 90° Turning Duct by an Endwall Boundary Layer Fence

ABSTRACT An endwall boundary layer fence technique was adapted to impr ove the aerothermal environment of a gas turbine passage. The shape optimization of the fence was performed to maximize the improvement. The turbine passage was simulated by a 90° turning duct (ReD=360,000). The main purpose of the present investigation was to focus on finding a endwall boundary layer fence with minimum total pressure loss in the passage and heat transfer coefficient on the endwall of the duct. Anothor objective function was to minimize the area on the endw all of the duct. An approximate optimization method was used for the investigation to secure th e computational efficiency. Results indicated that a significant improvement in aerodynamic environ ment can be achieved through the application of the fence. Improvement of the thermal environment was smaller than that of the aerodynamic enviroment.초 록 본 논문에서는 가스터빈 유로의 열유동 환경을 개선하기 위해 끝벽면 경계층 판을 이용한 방법을 적용하였으며, 이 방법에 의한 효과를 최대화하기 위해 경계층 판의 형상에 대한 최적화를 수행하였다. 터빈 유로를 모사하기 위해 90° 곡관을 이용하였다. 터빈 유로에서의 전압력 손실과 유로 끝벽면에서의 열전달 계수, 그리고 끝벽면 면적을 최소화하는 곙계층 판 형상 도출을 연구의 목적으로 하였으며, 최적화 과정의 효율성을 위해 근사 최적화 기법을 적용하였다. 연구결과를 통해, 최적화된 경계층 판에 의한 상당한 공력환경 개선을 확인할 수 있었으며, 열환경 개선 정도는 공력환경 개선정도에 비해 작게 나타났다.Key Words: Endwall Boundary Layer Fence(끝벽면 곙계층 판), Optimization(최적화), Secondary Flow(2차 유동), 90° Turning Duct(90° 곡관)

Controlling the Horseshoe Vortex by the Leading-Edge Fence at a Generic Wing-Body Junction

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses generated in the cascade of a turbine. Therefore, these are important part for improving a turbine efficiency. As well, many studies have been performed to decrease the secondary flow losses. The present study deals with the leading edge fences on a wing-body to decrease a horseshoe vortex, one of the factors to generate the secondary flow losses, and investigates the characteristics of the generated horseshoe vortex as the shape factors, such as the installed height, and length of the fence. The study was investigated using . Total pressure loss coefficient was improved about 4.0 % at the best case than the baseline.