• 한국전산유체공학회지
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• 제14권3호
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• pp.25-32
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• 2009

The present paper focuses on the analysis of aero-acoustics characteristic by appling different four boundary conditions. The high-order and high-resolution numerical schemes are used for discrete accurate computation of compressible flow. The four boundary conditions include extrapolation, characteristic boundary condition, zonal characteristic boundary condition. These boundary conditions are applied to the computation of two dimensional circular cylinder flows with Mach number of 0.3 and Reynolds number of 400. The computation results are validated against measurement data and other computation results for the Strouhal frequency of vortex shedding, the mean drag coefficient and root-mean-square lift for the unsteady periodic flow regime. The characteristics of secondary frequency is predicted by three kinds of boundary conditions.

• 설비공학논문집
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• 제2권1호
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• pp.63-73
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• 1990

A numerical analysis of initial unsteady state flow and heat transfer in an enclosed cavity has been performed by the Modified QUICK Scheme. The stable QUICK Scheme which modified the coefficient always to be positive is included in this numerical analysis. The implicit method is applied to solve the unsteady state flow; between iterations the PISO (Pressure - Implicit with Splitting of Operators) algorithm is employed to correct and update the velocity and pressure fields on a staggered grid. The accuracy of the Modified QUICK Scheme is proved by applying fewer grid systems than those which Ghia et al. and Davis applied. The initial unsteady mixed convection in an enclosed cavity is analyzed using the above numerical procedure. This study focuses on the development of the large main vortex and secondary vortex in forced convection, the effects of the Rayleigh Number in natural convection and the relative direction of the forced and natural convection.

• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.279-284
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• 2010

Tip clearance losses occur in every turbomachine. To estimate the losses in efficiency it is important to understand the mechanism of this secondary flow. Tip clearance losses are mainly caused by a spiral vortex formed on the suction side of the blade of a turbomachine, which induces a drag and also has an influence on the incident flow of the blades. In this paper a physical based scaling method is developed out of an analytical ansatz for the tip clearance losses. This scaling method is validated by measurements on an axial fan with five different tip clearances.

• 대한기계학회논문집
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• 제16권2호
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• pp.302-312
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• 1992

Three dimensional velocity measurements of a 35.deg. inclined jet issuing into turbulent boundary layer on both concave and convex surfaces have been conducted. To investigate solely the effect of each curvature on the flow field, streamwise pressure variations are minimized by adjusting the shape of the opposite wall in the curved region. From the measured velocity components, streamwise mean vorticities are calculated to determine jet-crossflow interface. The results on convex surface show that the injected jet is separated from the wall and the bound vortex maintains its structure far downstream. On concave surface, the secondary flow in the jet cross-sections are enhanced and in some downstream region from the jet exit, the flow on the concave surface has been developed to Taylor-Gortler vortices

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.157-159
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• 2008

An numerical investigation of the flow characteristics inside a diffusing S-duct inlet with and without vortex generators(VGs) was conducted. The primary discussion herein focuses on development of secondary flow in the S-duct with and without VGs, pressure recovery and distortion at the exit are also discussed. Full three-dimensional Navier-Stokes equations are solved using finite volume method and $k-\varepsilon$ turbulence model is employed. In order to validate the credibility of the numerical methods, predicted results of surface pressure are compared with flight test for the S-duct inlet without VGs, and it shows fairly good agreement. The result shows that VGs alter the flow characteristics in the S-duct and are effective in reducing distortion and ineffective in improving pressure recovery.

• 대한기계학회논문집B
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• 제22권1호
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• pp.12-24
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• 1998

The paper presents the mechanism of secondary flows and the associated total pressure losses occurring in turbine cascades with turning angle of about 127 and 77 degree. Velocity and pressure measurements are taken in seven traverse planes through the cascade passage using a prism type five hole probe. Oil-film flow visualization is also conducted on blade and endwall surfaces. The characteristics of the limiting streamlines show that the three dimensional separation is an important flow feature of endwall and blade surfaces. The larger turning results in much stronger contribution of the secondary flows to the loss developing mechanism. A large part of the endwall loss region at downstream pressure side is found to be very thin when compared to that of the cascade inlet and suction side endwall. Evolution of overall loss starts quite early within the cascade and the rate of the loss growth is much larger in the blade of large turning angle than in the blade of small turning angle.

• 한국추진공학회지
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• 제7권3호
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• pp.45-52
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• 2003

원추형 초음속 노즐 확산부에 이차유동이 음속으로 분출될 때 나타나는 노즐 내부 유동장에 대한 수치적 연구가 이루어졌다. 대수-난류모델과 $\kappa$-$\varepsilon$ 모델을 사용한 레이놀즈-평균 Navier-Stokes 방정식을 계산함으로서 노즐 내부에서 나타나는 충격파와 경계층의 간섭에 의한 3 차원 유동장을 해석하였다. 얻어진 수치해석의 결과는 동일한 조건에서 수행된 실험결과와 잘 일치하고 있음이 판명되었다. 이차유동의 분출압력 변화가 충격파와 경계층의 간섭과 함께 노즐내부 유동장 구조에 미치는 영향을 평가하였다. 아울러 충격파 간섭 후방에서 나타나는 와류유동 구조와 벽면 압력분포에 관한 정보를 얻었다.

• 한국항공우주학회지
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• 제31권9호
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• pp.1-8
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• 2003

연장된 앞전을 갖는 삼각날개 위에서 시위방향의 여러 위치에서 3축 hot 필름 풍속계를 사용하여 속도장 데이터를 획득하였다. 속도장 데이터는 받음각 24도와 32도에 대하여 중심 시위선을 기준으로 한 레이놀즈수 $1.76{\times}10^6$에서 날개면에 수직한 유동단면에서 측정하였다. 3축 hot 필름 프로브에 의한 세 가지 속도 성분을 측정함으로써 연장된 앞전을 갖는 삼각날개에서의 와류장을 정량적으로 분석할 수 있었다. 날개 와류와 LEX 와류는 평균 축방향 속도가 국소 최고 속도를 갖는 영역에 존재하였다. 아울러, 앞전 근처의 날개면 위에서 주와류와 반대 방향으로 회전하는 이차와류의 생성을 관찰할 수 있었다. 측정 프로브의 유동장에의 삽입은 와류 중심 위치에 크게 영향을 주지 않음을 알 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.546-552
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• 2001

The heat transfer and flow measurements on a pedestal encountered in chip cooling. A uniform wall temperature boundary condition at the plate surface and on a pedestal was created using shroud method. Liquid crystal was used to measure the plate surface temperature. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the dimensionless pedestal diameter-to-height (H/D) from 0 to 1.0. The results show that the Nusselt number distributions at the near the pedestal exhibit secondary maxima at $r/d{\cong}1.0\;and\;1.5$. The formation of the secondary maxima is attributed to an create in the vortex by the pedestal.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.284-289
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• 2002

The objective of this study is to document the secondary flow and the total pressure loss distribution in the contoured endwall installed linear turbine cascade passage and to propose an appropriate height of the contoured endwall which shows the best loss reduction among the simulated contoured endwall. In this study, three different contoured endwalls have been tested which have different height. This study was performed by numerical method and the result showed the contoured endwall which has the height of $5\%$ of the axial chord showed the best loss reduction rate.