서지주요정보
경계층 천이 현상을 계산하기 위한 난류 모형의 개발 = Development of k-ε model for prediction of transitional boundary-layer flows
서명 / 저자 경계층 천이 현상을 계산하기 위한 난류 모형의 개발 = Development of k-ε model for prediction of transitional boundary-layer flows / 백성구.
저자명 백성구 ; Baek, Seong-Gu
발행사항 [대전 : 한국과학기술원, 2002].
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8013317

소장위치/청구기호

학술문화관(문화관) 보존서고

DME 02027

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A modified κ-ε model is proposed for calculating transitional boundary layer flows. In order to develop the eddy viscosity model for the problem, the flow region is divided into three regions; namely, pre-transition region, transition region and fully turbulence region. In the pre-transition region, since the turbulence does not yet attain its equilibrium state in which the eddy viscosity is proportional to the distance from the wall, it is postulated that a structure like the viscous sub-layer in the turulent boundary layer prevails across the boundary layer so that the eddy viscosity is proportional to the cube of the wall distance. Further it is assumed that as the turbulent spots that have appeared at the onset of transition grow with the downstream distance in the transition region, the dependency of the eddy viscosity on the wall-distance changes gradually from that in the pre-transition region to that in the fully turbulent state. Therefore, a universal variation of the near-wall intermittency factor in the transition region is employed to represent such a transition eddy viscosity in the transition region, bridging the two different states, pre-transition and turblence eddy viscosity. In addition, the model constant $C_ε1$ in the standard κ-ε model is modified to take into account the particular characteristics of turbulence in the transition region, derived from the assumption that the mean velocity has an similarity solution. And also, the effect of pressure gradient is taken into account in the stream-wise intermittency factor because it has an universal curve regardless of pressure gradient. From the intermittecny factor in various flows, Narshima`s intermittency function, F(γ), has been found to be proportional to $χ^n$ according to the extent of pressure gradient. Three basic empirical correlations of intermittency factor being analyzed according to the results of analysis on experimental data, the best one was chosen to calculate six benchmark cases of bypass-transition flows with different free-stream turbulence intensity under zero and abitray pressure gradients. In the present test calculations, since the governing equations are integrated from a point close to the leading edge in the pre-transition region, the initial and boundary conditions of κ and ε at the onset of transition are automatically supplied. Under zero pressure gradient, it was found that the profiles of mean velocity and turbulent intensity, local maximum of velocity fluctuations, their locations as well as the streamwise variation of integral properties such as skin friction, shape factor and maximum velocity fluctuations are very satisfactorily predicted throughout the flow regions. Similarily the prediction under changing pressure gradient was also good agreement except the later part of the transition region, where better correlation is needed to improve the overall performance. Additionally, the experiment with a flat plate was conducted to verify the present modeling concept of having two diffrenent scales at least and to give available experimental data.

서지기타정보

서지기타정보
청구기호 {DME 02027
형태사항 viii, 124 p. : 삽도 ; 26 cm
언어 한국어
일반주기 부록 : A, 저레이놀즈 k-ε 난류 모형. - B, 좌표 변환
저자명의 영문표기 : Seong-Gu Baek
지도교수의 한글표기 : 정명균
지도교수의 영문표기 : Myung-Kyoon Chung
수록잡지명 : "$k-\epsilon$ model for predicting transitional boundary-layer flows under zero pressure-gradient". AIAA journal, v.39 no.9, pp.1699-1706 (2001)
학위논문 학위논문(박사) - 한국과학기술원 : 기계공학전공,
서지주기 참고문헌 : 107-113
주제 천이 경계층
난류 모형
천이이전영역
간헐도
transitional boundary layer
turbulence model
pre-transition region
intermittency
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