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Science China(Technological Sciences) 2003年第6期46卷 661-670页

作者：王沫然李志信 Department of Engineering Mechanics Tsinghua University Beijing 100084 China

The similarity of ideal gas flow at different scales is investigated analytically and nu-merically. With the compressible and rarefied effects considered, two dimensionless parameters, Mach number and Knudsen number, are proposed as the similarity criterions, because the Rey-nolds number can be expressed by the Mach number and the Knudsen number of ideal gases. A DSMC method is used to simulate flows at different scales with the same Ma and Kn, including subsonic channel flows and the supersonic flows over a hot plate. Comparisons between the re-sults of different scales show that the normalized fields of macroscopic quantities are the same. This confirms the similarity. Especially, the results indicate that the micro flow are similar to the rarefied flow of ideal gas, which suggests that many transformations are available from the existing rarefied flow results to the micro flow.

关键词： similarity, ideal gas flow, direct simulation Monte Carlo.

The study on Sanmenxia annual flow forecasting in the Yellow River with mix regression model

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Science China(Technological Sciences) 2004年第Z1期47卷 118-126页

作者： JIANG Xiaohui1, LIU Changming1,2, WANG Yu3 & WANG Hongrui1 1. Beijing Normal University, Beijing 100875, China 2. Institute of Geographic Science and Natural Resources, Chinese Academy of Sciences, Beijing 100101, China 3. Reconnaissance, Planning, Design and Research Institute, YRCC, Zhengzhou 450003, China Beijing Normal University Beijing China Institute of Geographic Science and Natural Resources Chinese Academy of Sciences Beijing China Reconnaissance Planning Design and Research Institute YRCC Zhengzhou China

This paper established mix regression model for simulating annual flow, in which annual runoff is auto-regression factor, precipitation, air temperature and water consumption are regression factors; we adopted 9 hypothesis climate change schemes to forecast the change of annual flow of Sanmenxia Station. The results show : (1) When temperature is steady, the average annual runoff will increase by 8.3% if precipitation increases by 10%; when precipitation decreases by 10%, the average annual runoff will decrease by 8.2%; when precipitation is steady, the average annual runoff will decrease by 2.4% if temperature increases 1℃; if temperature decreases 1℃, runoff will increase by 1.2%. The mix regression model can well simulate annual runoff. (2) As to 9 different temperature and precipitation scenarios, scenario 9 is the most adverse to the runoff of Sanmenxia Station of Yellow River; i.e. temperature increases 1℃ and precipitation decreases by 10%. Under this condition, the simulated average annual runoff decreases by 10.8%. On the contrary, scenario 1 is the best to the enhancement of runoff; i.e. when temperature decreases 1 ℃ precipitation will increase by 10%, which will make the annual runoff of Sanmenxia increase by 10.6%.

关键词： forecast annual flow, mix regression model, Sanmenxia Station

Experimental study on two-phase gas-liquid flow patterns at normal and reduced gravity conditions

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Science China(Technological Sciences) 2001年第5期44卷 553-560页

作者：赵建福解京昌林海胡文瑞 National Microgravity Laboratory Institute of Mechanics Chinese Academy of Sciences Beijing China

Experimental studies have been performed for horizontal two-phase air-water flows at nor-mal and reduced gravity conditions in a square cross-section channel. The experiments at reducedgravity are conducted on board the Russian IL-76 reduced gravity airplane. Four flow patterns, namelybubble, slug, slug-annular transition and annular flows, are observed depending on the liquid and gassuperficial velocities at both conditions. Semi-theoretical Weber number model is developed to includethe shape influence on the slug-annular transition. It is shown that its prediction is in reasonable agree-ment with the experimental slug-annular transition under both conditions. For the case of two-phasegas-liquid flow with large value of the Froude number, the drift-flux model can predict well the observedboundary between bubble and slug flows.

关键词： microgravity, two-phase gas-liquid flow, flow pattern, non-circular cross-section.

Experimental study on visualization of the flow field in microtube

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Science China(Technological Sciences) 2005年第5期48卷 521-529页

作者： LIU Zhigang ZHAO Yaohua Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100080 China Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100080 China

An experimental study was conducted to visualize the flow field and confirm the transitional Reynolds number from laminar to turbulent flow, as distilled water flows through quartz glass microtubes with inner diameter 315 and 520 μm. With gentian violet as colorant, the flow field pictures in the microtube, and therefore, is shot by a CCD camera with a microscope at different Reynolds numbers. Pressure drop data were also used to characterize the friction factor for those microtubes in the Reynolds number range of 200―2300. The experimental results clearly showed that the flow in the microtube was the laminar state and the friction factors agreed well with the Poiseuille equations when the Reynolds number was low. As the Reynolds number was larger than 1200 and 1500 for the microtube with inner diameter 315 and 520 μm, respectively, the friction factor departed from the classical laminar solution due to the earlier transition from laminar to turbulent flow. The flow turned into full turbulent when the Reynolds number reached 1500―1800.

关键词： visual experiment, microtube, microscale flow, friction factor, turbulent transition.

Immortal solution of the Ricci flow

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Science China Mathematics 2005年第Z1期48卷 217-224页

作者： RUAN Qihua & CHEN Zhihua Department of Applied Mathematics, Tongji University, Shanghai 200092, China Department of Mathematics, Putian College, Putian 351100, China Department of Applied Mathematics Tongji University Shanghai China Department of Mathematics Putian College Putian China

For any complete noncompact Kahler manifold with nonnegative and bounded holomorphic bisectional curvature, we provide the necessary and sufficient condition for the immortal solution to the Ricci flow.

关键词： Ricci flow, immortal solution, holomorphic bisectional curvature.

Water demand for ecosystem protection in rivers with hyper-concentrated sediment-laden flow

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Science China(Technological Sciences) 2004年第Z1期47卷 186-198页

作者： LUO Huaming, LI Tianhong, NI Jinren & WANG Yudong Department of Environmental Engineering, Peking University, Beijing 100871, China The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Beijing 100871, China Department of Environmental Engineering Peking University Beijing China The Key Laboratory of Water and Sediment Sciences Ministry of Education Beijing China

Sediment transport is one of the main concerns in a river system with hyper-concentrated flows. Therefore, the water use for sediment transport must be considered in study on the water demand for river ecosystem. The conventional methods for calculating the Minimum Water Demand for River Ecosystem (MWDRE) are not appropriate for rivers with high sediment concentration. This paper studied the MWDRE in wet season, dry season and the whole year under different water-and-sediment conditions in the Lower Yellow River, which is regarded as a typical river with sediment-laden flows. The characteristics of MWDRE in the river are analyzed. Firstly, the water demand for sediment transport (WDST) is much larger than the demands for other riverine functions, the WDST accounts for the absolute majority of the MWDRE. Secondly, in wet season when the WDST is satisfied, not only most of the annual incoming sediment can be transported downstream, but also the water demands for other river functions can be satisfied automatically, so that the MWDRE in wet season is identical to the WDST. Thirdly, in dry season, when the WDST is satisfied, the water demands for other river functions can also be satisfied, but the low sediment transport efficiency results in significant waste of water resources. According to these characteristics and aiming at decreasing sediment deposition in the riverbed and improving the utilization efficiency of water resources, hydrological engineering works can be used to regulate or control flow and sediment so that the sediment incoming in dry season can be accumulated and be transported downstream intensively and thus efficiently in wet season.

关键词： sediment-laden flow, the Lower Yellow River, water demand for river ecosystem, water demand for sediment transport

Rheological effect on thermocapillary flow of a liquid film jet painted on a moving boundary

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Science China Mathematics 2002年第9期45卷 1171-1182页

作者：胡文瑞许为厚 National Microgravity Laboratory/CAS Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China Dept. Math. Ctr. Sci. Computation Hong Kong Univ. of Sci. and Technol. Hong Kong Hong Kong

In the present paper, a liquid (or melt) film of relatively high temperature ejected from a vessel and painted on the moving solid film is analyzed by using the second-order fluid model of the non-Newtonian fluid. The thermocapillary flow driven by the temperature gradient on the free surface of a Newtonian liquid film was discussed before. The effect of rheological fluid on thermocapillary flow is considered in the present paper. The analysis is based on the approximations of lubrication theory and perturbation theory. The equation of liquid height and the process of thermal hydrodynamics of the non-Newtonian liquid film are obtained, and the case of weak effect of the rheological fluid is solved in detail.

关键词： die swell, thermocapillary flow, non-Newtonian fluid, film jet.

Study on two-phase countercurrent flow and transport phenomenon in PEM of a direct methanol fuel cell

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Science China(Technological Sciences) 2006年第1期49卷 102-114页

作者： WANG Jiang SHI Mingheng Department of Power Engineering Southeast University Nanjing 210096 China Department of Power Engineering Southeast University Nanjing 210096 China

Based on the requirement of water management for a direct methanol fuel cell, this paper analyzes qualitatively the mechanism of occurrence and development of a two-phase countercurrent flow with corresponding transport phenomenon in the PEM. A one-dimensional, steady state quantitative model of heat and mass transfer in internal volumetric ohmic heating porous media saturated by liquid and vapor phases is developed. The effects of capillarity, electro-osmotic drag and phase change are included. Two im-portant formulas to calculate the theoretical length of two-phase zone δ t and determine the critical criterion |?ω /γ |cr for dryout in PEM are deduced. By use of these two dimen-sionless parameters, dryout of PEM can be easily predicted. Theoretical temperature, pressure and saturation profiles within the two-phase region are obtained numerically, which can help to explore the performance of a DMFC operating in its ohmic polarization region. The simulation results can be used to determine the catalyst content of cathode catalyst layer and the corresponding optimal thickness of PEM.

关键词： direct methanol fuel cell, porous media, two-phase countercurrent flow, dryout.

Numerical study of multiple periodic flow states in spherical Couette flow

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Science China Mathematics 2004年第Z1期47卷 81-91页

作者： YUAN Li ICMSEC & LSEC Academy of Mathematics and System Sciences Chinese Academy of Sciences Beijing 100080 China

The supercritical flow states of the spherical Couette flow between two concentric spheres with the inner sphere rotating are investigated via direct numerical simulation using a three-dimensional finite difference method. For comparison with experiments of Nakabayashi et al. And Wimmer, a narrow gap and a medium gap with clearance ratio β=0.06 and 0.18 respectively areconsidered for the Reynolds number range covering the first Hopfbifurcation point. With adequate initial conditions and temporaryimposition of small wave-type perturbation, multiple periodicflow states with three different pair numbers of spiralTaylor-G{ortler (TG) vortices have been simulated successfullyfor β=0.06, of which the 1-pair and 2-pair of spiral Tgvortices are newly obtained. Three different periodic flow stateswith shear waves, Stuart vortices or wavy outflow boundary, have been obtained for β=0.18. Analysis of the numerical resultsreveals these higher flow modes in terms of fundamental frequency,wave number and spatial structure.

关键词： spherical Couette flow, non-unique flow solutions,spiral Taylor-G{o}rtler vortices, shear waves, Stuart vortices.