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Analytical　and　Numerical　Study　on　the　Uniformity　of　Temperature　Difference　Field　in　Heat　Exchangers

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Journal of Thermal Science 1995年第2期4卷 104-108页

作者： Zhi－XinLi Da－XiXiong 等 departmentofengineeringmechanics TsinghuaUniversity departmentofengineeringmechanics TsinghuaUniversi

The relations of the uniformity factor of temperature difference field with the effectiveness of heat exchangers were studied analytically and numerically. The results for eleven kinds of heat exchangers show that the more uniform the temperature difference field, the higher the effectiveness of heat exchanger for a given Ntu and Cr.

关键词： heat exchanger uniformity of TDF effectiveness.

Large Eddy Simulation of SGS Turbulent Kinetic Energy and SGS Turbulent Dissipation in a Backward-Facing Step Turbulent Flow

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Chinese Physics Letters 2004年第9期21卷 1773-1776页

作者：王兵张会强王希麟 departmentofengineeringmechanics TsinghuaUniversityBeijing100084

The instantaneous and time-averaged statistic characteristics of the sub-grid scale (SGS) turbulent kinetic energy and SGS dissipation in a backward-facing step turbulent flow have been studied by large eddy simulation. The SGS turbulent kinetic energy and SGS turbulent dissipation vary in different flow regions and decrease with the flow developing spatially. The fluid molecular dissipation shares about 14% to 28% of the whole dissipation.

关键词： Turbulent flow

Effect of Lateral Pressure on the Non-Linear Behaviour of PZT Ceramics

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Chinese Physics Letters 2003年第12期20卷 2250-2251页

作者：李法新方岱宁冯雪 departmentofengineeringmechanics TsinghuaUniversityBeijing100084

The non-linear behaviour of PZT-5 ceramics under coupled electrical–mechanical loading (E3 and σ11) is experimentally studied. The effect of different levels of compressive stress on the electrical–mechanical response is examined. With the increase of compressive stress, shapes of the electric hysteresis loop and the butterfly curve are slightly changed, while the reversed butterfly curve (ε11 vs E3) varies significantly, and the value of the piezoelectric constant d31 decreases evidently. Based on these experimental results, a simple design is proposed to improve the sensitivity and reliability of the submarine detectors and sensors.

关键词： Effect Lateral Pressure Non-Linear Behaviour PZT Ceramics

Mechanism for Influence of Nose Bluntness on Asymmetric Vortices

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Chinese Physics Letters 2004年第11期21卷 2223-2226页

作者：王刚梁新刚 departmentofengineeringmechanics TsinghuaUniversityBeijing100084

Pressure distributions on slender bodies are measured at various roll angles; it is found that the side loads on the blunted-nose slender body are as small as one-third of that on a pointed-nose one, or even zero at some roll angles. Numerical simulation shows that different flow structures are generated on the leeside of the bodies with different noses. The results confirm that a structure of U-shaped horseshoe vortex develops on the top of the blunted nose due to the closed type of surface flow separation. The shear layer separated from the nose is entrapped into the horseshoe vortex core and forms two main vortices on the two sides of the body. The function of this structure is to hold in the two main nose vortices and to restrict the emergence of asymmetry.

关键词： Vortex flow

SYMMETRIC MODE INSTABILITY OF THE SLIPFLOW MODEL FOR FLOWS IN A MICROCHANNEL WITH A VANISHING REYNOLDS NUMBER

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Acta Mechanica Sinica 2003年第5期19卷 420-426页

作者：甘才俊吴子牛 departmentofengineeringmechanics TsinghuaUniversity100084China

The slipflow model is usually used to study microflows when the Knudsen number lies between 0.01 and 0.1. The instability due to microscale effect seems to have never been studied *** this paper we present preliminary results for the instability (not physical instability) of this model when applied to microchannel flow with a vanishing Reynolds number. The present paper is restricted to symmetrical mode. Both first-order and second-order slip boundary conditions will be considered.

关键词： slipflow model microchannel instability

Dual Role of Viscosity During Start-Up of a Maxwell Fluid in a Pipe

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Chinese Physics Letters 2004年第1期21卷 114-116页

作者：任玲朱克勤 departmentofengineeringmechanics TsinghuaUniversityBeijing100084

Based on the exact solution of start-up flow of Maxwell fluids in a long circular straight pipe, the effect of viscosity on the time of flow establishment is analysed. It is found that the viscosity of Maxwell fluids plays a dual role. A key parameter is the dimensionless relaxation time . For 00.0432, the viscosity mainly plays a role of strengthening the oscillation, and the time of flow establishment increases with the incremental viscosity.

关键词： Viscosity

Bifurcation,Bi—instability and Area Principle for the Solitary Waves of the Nonlinear Wave Equation with Quartic Polynomial Potential

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Chinese Physics Letters 2002年第7期19卷 885-888页

作者：化存才刘延柱 departmentofengineeringmechanics ShanghaiJiaoTongUniversityShanghai200030

For the nonlinear wave equation with quartic polynomial potential, bifurcation, bi-instability and solitary waves are investigated. An area principle based on the bifurcation diagram is found for the existence of bright and dark solitary waves and shock waves. The simple forms of solitary wave solutions are given by an approximate analytic method.

关键词： Solitons

A High-Order Meshless Bhatnagar-Gross-Krook Scheme Based on Point Collocation

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Chinese Physics Letters 2004年第2期21卷 233-236页

作者：孙喜明何枫 departmentofengineeringmechanics TsinghuaUniversityBeijing100084

A point collocation method is combined with the Bhatnagar–Gross–Krook (BGK) scheme. The point collocation method is based on reproducing kernel approximations. The BGK scheme developed is evaluated under the finite difference method framework. After the construction of local equilibrium distribution function, the second-order accurate least-square kinetic upwind method is employed to improve the accuracy. Some test cases are explored to validate this meshless method.

关键词： Finite difference method

Instability of Taylor-Couette Flow of Electrorheological Fluid

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Chinese Physics Letters 2004年第7期21卷 1388-1390页

作者： PENGJie ZHUKe-Qin departmentofengineeringmechanics TsinghuaUniversityBeijing100084

A linearized instability analysis of Taylor–Couette flow between two rotating concentric cylinders of an electrorheological (ER) fluid is carried out. The ER fluid exhibits a yield stress in addition to the plastic viscosity when an extra electric-field is applied. It can be found that the yield stress plays a dual role in the flow instability. The possibility of the yield surface falling between the cylinders is analysed. Although small waves appeared on the yielded surface is considered, the yielded surface, which has been treated as a free surface, has little effect on the flow instability. The effects of axisymmetric perturbation on the flow instability are presented due to the axisymmetric of the basic flow. The parameter β in the yield stress formula of the ER fluid is shown to have distinct effects on the flow instability characteristics.

关键词： Electrorheological fluids