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Numerical Simulation of Unsteady Discharge flow with fluctuation in Positive Discharge Blower

Chinese Journal of Mechanical Engineering 2009年第2期22卷 214-220页

作者： LIU Zhengxia WANG Dou XU Lianhuan School of Mechanical Engineering Tianjin University Tianjin 300072 China State Key Laboratory of Engines Tianjin University Tianjin 300072 China Xi＇an Shaangu Power Co. Ltd Xi＇an 710075 China Shandong Power Equipment Company Jinan 250022 China

The operating performance of positive discharge blower is markedly influenced by the pulsation of the discharge flow, but difficult to be measured with experimental methods. The internal and discharge flow of positive discharge blower with involute type three-lobe are numerically investigated, both in air cooling and countercurrent cooling conditions by means of computational fluid dynamics （CFD）. The unsteady compressible flow equations are solved using RNG x-ε turbulent model. The finite difference method and the second order upwind difference scheme are applied into discrete equations. In the numerical simulation, the dynamic mesh techniques are used to approach the rotating displacement of cell cubage and the alterability of inlet, outlet flow area. The non-uniform mesh is applied to the rotor-stator coupled area. The reliability of the numerical method is verified by simulating the inner flow and comparing with the semi-empirical theory. The flow flux curves and the distributing of velocity vector showed obvious vortex motion in all the discharge process, both in air cooling and countercurrent cooling conditions. These vortexes with different positions, intension and numbers at different rotating angles have remarkable influences on the discharge flux. For air cooling, the vortex produced a second pulsation with big-amplitude in a cycle, and led to the early appearance of maximum of backflow. For countercurrent cooling, the frequency of pulsation increased due to the pre-inflow, but the backflow at the outlet is prevented, also the pulsation strength has greatly decreased.

关键词： countercurrent cooling positive discharge blower dynamic mashing techniques flow fluctuation mumerical simulation

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Study on the characteristics of flow resistance under the condition of low frequency flow fluctuation

Study on the characteristics of flow resistance under the co...

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作者： LIU Yu-sheng GAO Pu-zhen TAN Si-chao ZHANG Jia-jia National Key Subject Laboratory of Nuclear Safety and Simulation Technology Harbin Engineering University

The circulation of coolant in the cooling system of a nuclear reactor,under earthquake conditions,is a process of pulsating *** the fluctuating flow occurs in the loop,the fluid flow and heat transfer in the core are affected,making the study of flow fluctuation more important for practical *** of flow resistance are investigated experimentally on a horizontal rectangular channel and a circular tube with a periodically fluctuating *** results are compared with the flow resistance characteristics of the steady state,showing that there is a relatively large difference between the results under a steady flow and a transient *** article analyzes the influences of the flow fluctuation period and of the relative amplitude on the resistance characteristics of a circular tube *** results show that under the condition of flow fluctuation,a phase difference exists between flow rate and pressure *** results further show that the smaller the flow fluctuation period is,the larger the flow fluctuation relative amplitude will be,and the more influence the flow fluctuation will have on the fluid ***,an empirical correlation expressed as a function of the Reynolds number,the dimensionless frequency parameter,and the relative amplitude,is proposed for calculating a time-averaged friction coefficient.

关键词： rectangular channel circle tube flow fluctuation resistance characteristics

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Variation in Grain Size Distribution in Debris flow

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Journal of Mountain Science 2015年第3期12卷 682-688页

作者： LI Yong WANG Bao-liang ZHOU Xiao-jun GOU Wan-chun Key Laboratory of Mountain Hazards and Surface Process Chinese Academy of Sciences Institute of Mountain Hazards and Environment Chinese Academy of Sciences Graduate University of Chinese Academy of Sciences China Merchants Chongqing Communications Research & Design Institute

Grain composition of debris flow varies considerably from fluid to deposit, making it uncertain to estimate flow properties （e.g., density, velocity and discharge） using deposit as done in practice. Tracing the variation of grain composition is thus more important than estimating some certain properties of flow because every debris flow event consists of a series of surges that are distinct in properties and flow regimes. We find that the materials of debris flows, both the fluid and the source soils, satisfy a universal grain size distribution （GSD） in a form of P （D） = CD-zexp（-D/Dc）, where the parameters C, p and De are determined by fitting the function to the grain size frequency. A small At implies a small porosity and possible high excess pore pressure in flow; and a large D~ means a wide range of grain composition and hence a high sediment concentration. flow density increases as 11 decreases or Dc increases, in a power law form. A debris flow always achieves a state of certain mobility and density that can be well described by the coupling of p and Dc, which imposes a constraint on the fluctuations of flow surges. The GSD also describes the changes in grain composition in that it is always satisfied during the course of debris flow developing. Numerical simulation using the GSD can well illustrate the variation ofμ and Dc from source soils to deposits.

关键词： Debris flow Grain size distribution flow fluctuation Power-law constraints

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Pressure Drop fluctuations in Periodically Fluctuating Pipe flow

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Journal of Marine Science and Application 2010年第3期9卷 317-322页

作者：高璞珍刘廷浩杨婷谭思超 College of Nuclear Science and Technology Harbin Engineering University

Experiments were conducted to study characteristics of flow when flow is *** experimental results showed a phase difference between the flow rate and the pressure drop *** phase difference between the fluctuating flow rate and pressure drop was analyzed for laminar *** showed that the phase difference changes with the period of the flow fluctuation, the pipe radius, the density and the dynamic viscosity of the *** pipe flow was then numerically *** of the numerical simulation were compared with theoretical values and experimental *** was shown that, when the flow rate fluctuates with time as a sine wave, the pressure drop fluctuates with the same periodicity, and there is a phase difference between them.

关键词： flow fluctuation pressure drop flow rate phase difference

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