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오종식,Oh, Jongsik 한국유체기계학회 1999 한국유체기계학회 논문집 Vol.2 No.3
In the present numerical analysis, investigation of the effect of blade loadings from design shape on the slip factor variation was studied. Both the Eckardt radial bladed impeller and the backswept impeller were analyzed. In addition, a new design of the blade profile was arbitrarily attempted to generate a center-loading pattern in the original backswept impeller. Three dimensional compressible Navier-Stokes flow analysis with the Baldwin-Lomax turbulence model was applied to get the numerical slip factor at each impeller exit plane using the mass-averaging technique. The numerical slip (actors are in good agreement with the experimental ones and the Wiesner's slip factors deviate further from the numerical and experimental ones in both backswept impellers. Deviation angles and meridional channel loadings are found in no relation with the trend of change of the slip factor. Blade-to-blade loadings in midspan location are, however, found to have a direct relationship, especially at the sections where maximum loadings we to be expected. That information can be utilized in establishing an improved expression for slip factors in the future.
오종식,오군섭,유광택,Oh, Jong Sik,Oh, Koon Sup,Yoo, Kwang Taek 한국유체기계학회 2000 한국유체기계학회 논문집 Vol.3 No.1
선박용 디젤엔진에 정착되어 사용되는 기존의 터보차져 성능을 개량하기 위하여 압축기만의 수정개발을 수행한 결과를 요약하면 다음과 같다. (1) 터빈과의 싸이클 matching 작업을 통하여 기존의 압축기 성능에 비하여 $7\%$ 증가된 회전수와 $8\%$ 증가된 입구 공기유량으로 상향 조정되면서 효율의 큰 저하 없이 전압력비도 3.5 수준으로 증가되도록 설계점이 성공적으로 확정되었다. (2) 기존의 압축기 케이싱과 스크롤을 대부분 그대로 사용한다는 기하학적 제한조건하에서 3차원 공력 설계가 성공적으로 수행되었고, 설계된 임펠러는 3차원 압축성 난류 수치유동해석 과정을 통해 구체적인 내부 유동과 임펠러의 overall 성능을 확인하였다. (3) 터보차져 전용 시험리그에서 시제품을 성능시험한 결과, 전반적인 압축기의 성능곡선을 성공적으로 도출하였다. 대체적으로 전체 회전수별로 실험결과로 얻은 전압력비는 설계 예측치와 매우 잘 일치하는 모습을 볼 수 있었고, 단열효율의 경우, 실험치와 예측치가 서로 잘 일치하고 있었다. 설계의도대로 설계점에서의 압력비 상승과 유량의 증가 등은 만족스럽게 달성된 것으로 판단된다. (4) 베인디퓨져의 제작문제로 인하여 설계회전수에서의 surge와 choke margin이 설계의도와는 달리 좋지 않은 상태이다. 이는 본래 설계대로 베인디퓨져를 재제작하고 설치각의 크기를 조절함으로써 앞으로 진행될 추가시험에서 보완할 예정이다. Upgrade development of a high pressure ratio centrifugal compressor in marine engine turbochargers is presented. A new matched operating point at increased speed of rotation was determined through system cycle analysis using the exisitng test data of turbine performance. Under some severe restrictions for geometric parameters, the state-of-the-art methods of both aerodynamic design and CFD analysis were applied, in which only an impeller, a vaned diffusor and some part of casing wall were modified. Prototype hardware was fabricated and assembled for system performance tests. Excellent performance in pressure ratio and efficiency was obtained over whole speed region. Reduced surge and choke margin was, however, observed at design speed of rotation.
오종식(Oh Jong-Sik),강대언(Kang Dae-Eon),이원호(Yi Waon-Ho),이재연(Lee Jae-Yeon) 대한건축학회 2007 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.27 No.1
The purpose of this study is to analyze structural behavior of RC short-column and evaluate shear strength formular of each country, so five column specimens with variables of axial load ratio and shear reinforcement ratio are made and tested. From test results, in every specimen, bending cracks occurred initially in the middle part of specimens and they moved to upper and lower part of specimens. And shear cracks were originated from upper corner in diagonal direction, and they progressed fast and the specimens were failed. As the axial load ratio and shear reinforcement ratio increases, the shear strength increases. Applying test results to ACI Code, Euro Code and JBDPA Code, the ratios of experimental value to theoretical value are appeared in the range of 1.82~2.73, 1.76~2.56, 1.20~1.63 respectively. From this result, it is proved that ACI Code and Euro Code overestimates the shear strength of short column, compared with JBOPA Code.
Numerical Investigation of Secondary Flow in Centrifugal Compressor Stage
오종식(Justin Oh) 한국유체기계학회 2005 유체기계 연구개발 발표회 논문집 Vol.- No.-
? Wake is formed away from suction surface near shroud at impeller exit. ? Wake location is determined by a force balance from secondary flows : between blade passage vortex and tip leakage vortex. ? Pressure gradient drives secondary flow in the inducer region, while in the remaining region the following sources drive together : > Pressure gradient > Coriolis force > Tip leakage vortex ? Wake moves from shroud towards suction surface of diffuser vanes.
원심 압축기의 CFD를 위한 대표적인 Bench Mark
오종식(JongSik Oh) 한국유체기계학회 1999 유체기계 연구개발 발표회 논문집 Vol.- No.-
The importance of CFD work in the process of turbomachinery development has been continuously growing. It is therefore necessary to have some bench marks for validation purposes when any CFD codes are to be developed. In the present study, some public information on centrifugal compressor test results is collected to render useful data for the developers.
가스터빈용 소형 원심압축기의 탈설계점 성능에 관한 실험연구
오종식(JongSik Oh),이헌석(HeonSeok Lee),오군섭(KoonSup Oh) 한국유체기계학회 2000 유체기계 연구개발 발표회 논문집 Vol.- No.-
Off-design experimental performance was investigated for a small centrifugal compressor, whose impeller diameter is about 125㎜, used in an industrial gas turbine. Test rig was designed and manufactured with a radial inflow turbine and a combustor to supply driving power to the compressor. Static pressure was measured on the casing of the impeller, vaneless diffuser, vaned diffuser and volute. Total pressure was obtained using specially fabricated rakes at the vaned diffuser throat and exit. Circumferential nonuniformity was found, near surge, in the impeller, vaned diffuser and volute region. Spanwise nonuniform flow from the impeller affected the total pressure defects in the vaned diffuser region. Static pressure distortion in the circumferential direction in the volute was found near surge, where the minimum occurred near 140 degree position.
원심압축기의 임펠러의 Blockage와 Slip 특성에 관한 수치연구
오종식(JongSik Oh) 한국유체기계학회 2000 유체기계 연구개발 발표회 논문집 Vol.- No.-
As the second part of the author's study, the aerodynamic blockage and the slip factor of 8 centrifugal compressor impellers are investigated, when the flow rate is changed from numerical stall to choke, using three-dimensional Navier-Stokes analysis results. Based on all the exit blockage distributions, an improved model equation with two adjusting coefficients is developed for the use in design processes with the agile engineering purpose. A popular expression of constant slip factors, the Wiesner's equation, cannot be applied in design processes when more accurate prediction is strongly required at design and off-design points. Slip factor variation is found to be also influenced by the blade loadings at midspan. When the flow rate is changed, a pattern of the slip factor variations is assumed to be a simple form which can be explained using midspan blade loading distributions.