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Numerical analysis on heat transfer enhancement by longitudinal vortex based on field synergy principle

WU Junmei, TAO Wenquan

《能源前沿（英文）》 2007年第1卷第3期页码 365-369 doi: 10.1007/s11708-007-0055-1

摘要： Three-dimensional numerical simulation results are presented for a fin-and-tube heat transfer surface with vortex generators. The effects of the Reynolds number (from 800 to 2 000) and the attack angle (30º and 45º) of a delta winglet vortex generator are examined. The numerical results are analyzed on the basis of the field synergy principle to explain the inherent mechanism of heat transfer enhancement by longitudinal vortex. The secondary flow generated by the vortex generators causes the reduction of the intersection angle between the velocity and fluid temperature gradients. In addition, the computational evaluations indicate that the heat transfer enhancement of delta winglet pairs for an aligned tube bank fin-and-tube surface is more significant than that for a staggered tube bank fin-and-tube surface. The heat transfer enhancement of the delta winglet pairs with an attack angle of 45º is larger than that with an angle of 30º. The delta winglet pair with an attack angle of 45º leads to an increase in pressure drop, while the delta winglet pair with the 30º angle results in a slight decrease. The heat transfer enhancement under identical pumping power condition for the attack angle of 30º is larger than that for the attack angle of 45º either for staggered or for aligned tube bank arrangement.

关键词： computational inherent mechanism staggered decrease transfer surface

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Implementation aspects of a phase-field approach for brittle fracture

G. D. HUYNH, X. ZHUANG, H. NGUYEN-XUAN

《结构与土木工程前沿（英文）》 2019年第13卷第2期页码 417-428 doi: 10.1007/s11709-018-0477-3

摘要： This paper provides a comprehensive overview of a phase-field model of fracture in solid mechanics setting. We start reviewing the potential energy governing the whole process of fracture including crack initiation, branching or merging. Then, a discretization of system of equation is derived, in which the key aspect is that for the correctness of fracture phenomena, a split into tensile and compressive terms of the strain energy is performed, which allows crack to occur in tension, not in compression. For numerical analysis, standard finite element shape functions are used for both primary fields including displacements and phase field. A staggered scheme which solves the two fields of the problem separately is utilized for solution step and illustrated with a segment of Python code.

关键词： phase-field modeling FEM staggered scheme fracture

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Simulation of cross-flow-induced vibration of tube bundle by surface vorticity method

WANG Fenghao, JIANG Gedong, Lin John Zhang

《能源前沿（英文）》 2008年第2卷第3期页码 243-248 doi: 10.1007/s11708-008-0049-7

摘要： A fluid-structure interaction model based on Surface Vorticity Method (SVM) was used to study flow-induced vibrations of tube bundles in medium space ratio. The flow-induced vibrations of four tubes in a rotated square and a staggered tube bundle in three-row and five-column arrangements were simulated in the high sub-critical Reynolds number () range. The results on fluid forces, tube responses and vorticity maps were presented. The vorticity maps of the four rotated-square tubes changed dramatically when the rigid tubes were replaced by the flexible tubes. From the vorticity maps and vibration responses of the staggered tube bundle of different structural parameters, it was found that with the decrease of tube natural frequency, the maximal vibration response moved from the third row to the first. The results also showed that when more flexible tubes are used, the flow pattern changed drastically and the fluid-structure interaction imposed a dominant impact on the flow.

关键词： dominant sub-critical Reynolds staggered Vorticity three-row

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Optimum design of a channel roughened by dimples to improve cooling performance

Abdus SAMAD, Ki-Don LEE, Kwang-Yong KIM, Jin-Hyuk KIM,

《能源前沿（英文）》 2010年第4卷第2期页码 262-268 doi: 10.1007/s11708-010-0012-2

摘要： Staggered arrays of dimples imprinted on opposite surfaces of an internal flow channel have been formulated numerically to enhance turbulent heat transfer compromising with pressure drop. The channel is simulated with the help of three-dimensional Reynolds-averaged Navier-Stokes (RANS) analysis. Three non-dimensional design variables based on dimple size and channel dimensions and two objectives related to heat transfer and pressure drag have been considered for shape optimization. A weighted-sum method for multi-objective optimization is applied to integrate multiple objectives into a single objective and polynomial response surface approximation (RSA) coupling with a gradient based search algorithm has been implemented as optimization technique. By the present effort, heat transfer rate is increased much higher than pressure drop and the thermal performance also has shown improvement for the optimum design as compared to the reference one. The optimum design produces lower channel height, wider dimple spacing, and deeper dimple as compared to the reference one.

关键词： Staggered three-dimensional Reynolds-averaged multi-objective optimization reference transfer