Analysis of turbulent flow and heat transfer in channels roughened by two-dimensional ribs and three-dimensional blocks = 이차원 rib 또는 삼차원 block이 분포된 채널 내 난류 열 및 유동해석

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The characteristics of a turbulent flow and heat transfer in channels with two-dimensional ribs of different cross-sections and three-dimensional blocks in different relative positions are investigated in the context of surface roughness effects. Reynolds-averaged Navier-Stokes equations, coupled with the $k - ω - overline{t^2} - ε_t}$ four-equation turbulence model with near-wall treatment, are solved by a finite-volume method. Calculations are carried out for two-dimensional ribs with square, triangular, semicircular and wavy cross sections over a range of rib spacing (pitch) and Reynolds numbers. The pitch that yields maximum resistance is identified for each roughness. The resistance is highest for the square rib and lowest for a wave-like rib. For all cases, the space-averaged velocity profile exhibits a logarithmic region, with a roughness function that varies logarithmically with the roughness Reynolds number. The roughness function depends on the rib shape and pitch ratio but is independent of the absolute rib size. Analysis of channel flow with three-dimensional blocks reveals similar but more complex behavior. A logarithmic regime exists in the space-averaged velocity profile but with much smaller block heights compared to ribs. As the block cross-section changes from square to rectangular, the flow is severely disturbed and even smaller heights are needed for a logarithmic region to exist. When the logarithmic region exists, the staggered and non-staggered rib arrangements exhibit quite different flow characteristics but the differences tend to vanish as the block height is decreased. In general, the results suggest that a Reynolds-averaged numerical model with proper near-wall treatment of the turbulence model successfully describes the principal features of wall roughness that have hitherto fore been purview of experimental correlations. The heat transfer and the flow resistance are confirmed to move together and the highest heat transfer ...
Advisors
Choi, Do-HyungresearcherPatel, Virendra C.researcher최도형researcher
Description
한국과학기술원 : 기계공학전공,
Publisher
한국과학기술원
Issue Date
2005
Identifier
249364/325007  / 000995234
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 기계공학전공, 2005.8, [ xiii, 137 p. ]

Keywords

Turbulent heat transfer; Roughness function; Similarity law; Distributed roughness; RANS eqation; 4 방정식 난류 모델; 난류 열전달; 거칠기 함수; 상사성; 균일분포된 요철

URI
http://hdl.handle.net/10203/43575
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=249364&flag=dissertation
Appears in Collection
ME-Theses_Ph.D.(박사논문)
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