A NEW APPROACH TO THE SIMULATION OF UNSTEADY SUBCRITICAL FLOW

ＡＮＥＷＡＰＰＲＯＡＣＨＴＯＴＨＥＳＩＭＵＬＡＴＩＯＮＯＦＵＮＳＴＥＡＤＹＳＵＢＣＲＩＴＩＣＡＬＦＬＯＷ￥ＭａｏＺｅ－ｙｕ（ＤｅｐａｒｔｍｅｎｔｏｆＨｙｄｒａｕｌｉｃＥｎｇｉｎｅｅｒｉｎｇ，ＴｓｉｎｇｈｕａＵｎｉｖｅｒｓｉｔｙＢｅｉｊｉｎｇ１０００８...     

不稳定渗流浸润线计算在梦山水库的应用

以江西省新建县梦山水库为例,阐述了均质土坝(设计前)和砼心墙坝(设计后)的不稳定渗流浸润线计算的过程,并对计算结果进行了分析.     

COMPUTATION OF STEADY FLOW BY UNSTEADY FLOW APPROACH AND STEADY FLOW APPROACH

Steady water surface profile of gradually varied flow can be calculated using ei-ther a steady flow approach or an unsteady flow approach. The steady flow approach requires it-erative procedures which may have convergence problems unless the step size 1x is less than amaximum value △x. The unsteady flow approach based on the explicit characteristic method hasa stability problem unless △x is less than △x. A series of numerical experiments were carried outand the results of two approaches are compared.     

混凝土受压性能的均质细观数值模拟

将混凝土看作由骨料、砂浆及它们之间的界面组成的三相复合材料，在细观层次上建立了均质混凝土棱柱体试件的随机骨料模型，分别赋予细观单元弹脆性和弹塑性本构关系，研究了采用不同本构关系的混凝土棱柱体试件在单轴压缩荷载作用下的细观损伤演化过程，分析了宏观应力应变曲线的差异，并将计算结果与试验结果做了比较。结果表明：混凝土试件的破坏是由于细观损伤的积累导致的；界面相是混凝土材料内部最薄弱的地方；砂浆单元采用弹塑性本构关系时所得混凝土棱柱体受压的宏观应力－应变全曲线与试验结果吻合较好。     

ANALYSIS OF PULSATILE FLOW IN THE PARALLEL-PLATE FLOW CHAMBER WITH SPATIAL SHEAR STRESS GRADIENT

The Parallel-Plate Flow Chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells (ECs) exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.     

THE LINEAR HOMOGENEOUS FLOW MODEL FOR TWO-PHASE FLOW INSTABILITY IN BOILING CHANNELS

ＮＯＭＥＮＣＬＡＴＵＲＥＤ　ｉｎｎｅｒｄｉａｍｅｔｅｒ (ｍ)Ｑ　ｈｅａｔｆｌｕｘ (ｋｗ/ｍ2 )ｆ　ｆｒｉｃｔｉｏｎａｌｒｅｓｉｓｔａｎｃｅｃｏｅｆｆｉｃｉｅｎｔＴ　ｔｅｍｐｅｒａｔｕｒｅ (°Ｃ)Ｇ　ｍａｓｓｆｌｏｗｖｅｌｏｃｉｔｙ (ｋｇ/ｓ.ｍ2 )ｔ　ｔｉｍｅ (     

UNSTEADY FLOW OF NON-NEWTONIAN VISCO-ELASTIC FLUID IN DUAL-POROSITY MEDIA WITH THE FRACTIONAL DERIVATIVE

The fractional order derivative was introduced to the seepage flow research to establish the relaxation models of non-Newtonian viscoelastic fluids in dual porous media. The flow characteristics of non-Newtonian viscoelastic fluids through a dual porous medium were studied by using the Hankel transform, the discrete Laplace transform of sequential fractional derivatives and the generalized Mittag-Leffler function. Exact solutions were obtained for arbitrary fractional order derivative. The long-time and short-time asymptotic solutions for an infinite formation were also resulted. The pressure transient behavior of non-Newtonian viscoelastic fluids flow through an infinite dual porous media was studied by using Stehfest's inversion method of the numerical Laplace transform. It shows that the characteristics of the fluid flow are appreciably affected by the order of the fractional derivative.     

UNSTEADY FLOW OF POLYMER FLUID BETWEEN COAXIAL CYLINDERS

In the present paper an unsteady flow of polymer fluid,i.e.non-Newtonianfluid is studied.The constitutive equation of upper-convected Maxwell fluid is used.The varia-tional approach due to Kantorovich is used for the unsteady problem of the fluid.A special com-puter program“MACSYMA”is used to get the different approximation of the method of Kan-torovich.The present method developed is called Computational Analytical Method which isavailable for the scientific research.     

AN UNSTEADY SEEPAGE FLOW MODEL OF VISCO-ELASTIC POLYMER SOLUTION

With the consideration of the visco--elasticity, the adsorption effect and the variation of rheological parame ters, a seepage flow model of visco-elastic polymer solutions was established. The model was numerically treated with the finite difference method. Then curves of Bottom Hole Pressure (BHP) and formation pressure were drawn. The influences of the relaxation time, the injection rate, the permeability reduction co,efficient, the consistency coefficient and the power-law exponent of the injected fluid on pressure performance were analyzed. This study shows that it is necessary to consider the visco elasticity of non-Newtonian fluid in analyzing of pressure performance in the polymer flooding.     

UNSTEADY FLOW ANALYSIS AND EXPERIMENTAL INVESTIGATION OF AXIAL-FLOW PUMP

The three-dimensional unsteady turbulent flow in axial-flow pumps was simulated based on Navier-Stoke solver embedded with k-ε RNG turbulence model and SIMPLEC algorithm.Numerical results show that the unsteady prediction results are more accurate than the steady results,and the maximal error of unsteady prediction is only 4.54%.The time-domain spectrums show that the static pressure fluctuation curves at the inlet and outlet of the rotor and the outlet of the stator are periodic,and all have four peaks and four valleys.The pressure fluctuation amplitude increases from the hub to the tip at the inlet and outlet of the rotor,but decreases at the outlet of the stator.The pressure fluctuation amplitude is the greatest at the inlet of the rotor,and the average amplitude decreases sharply from the inlet to the outlet.The frequency spectrums obtained by Fast Fourier Transform(FFT) show that the dominant frequency is approximately equal to the blade passing frequency.The static pressure on the pressure side of hydrofoil on different stream surfaces remains almost consistent,and increases gradually from the blade inlet to the exit on the suction side at different time steps.The axial velocity distribution is periodic and is affected by the stator blade number at the rotor exit.The experimental results show that the flow is almost axial and the pre-rotation is very small at the rotor inlet under the conditions of 0.8 QN -1.2 QN.Due to the clearance leakage,the pressure,circulation and meridional velocity at the rotor outlet all decrease near the hub leakage and tip clearance regions.     

TIME DOMAIN SOLUTION OF UNSTEADY FLOW AROUND A SHIP

The unsteady flow around a ship advancing at constant speed is studied in time domain using a higher-order boundary element method. The Rankine source is employed and the ship hull and free surface are discretized into 8-node isoparametric elements. A modified Green formula is used to overcome the numerical difficulty arising from the singular or quasi-singular integrals in the integral equation. In the case of τ> 0. 25, a rigid wall condition is applied to the upstream and a numerical beach is applied downstream to absorb the outgoing waves. The numerical results are satisfactory, compared with the experimental results.     

NUMERICAL EXPERIMENTS ABOUT GROWTH OF THE ENERGY OF DISTURBANCE IN A BAROCLINIC FLOW

This article is concerned with the growth of energy of disturbances in a baroclinic flow within a finite time period. The implicit difference scheme was applied to the linearized vorticity equation, and the disturbance energy was computed for three kinds of vertical shears. It turns out that all the disturbance energy rapidly increases initially, and during the succeeding period there are several stages of growth and decay of energy of disturbances, and from a certain time on, all the disturbance energy begins to decrease.     

NUMERICAL MODELING OF UNSTEADY SEPARATING FLOW AND ITS EXPERIMENT VERIFICATION

A simulation of unsteady separating flow in an expanding flume is presented inthis paper.The numerical modeling is based on a general horizontal 2-D mathematical model ofunsteady flow.It is verified that the flow pattern,whirlpool length and maximum reversalvelocity reasonably agree with the data from flume tests and this result could be an additionalproof for the validity of the earlier developed mathematical model.     

STUDY AND APPLICATION OF STEADY FLOW AND UNSTEADY FLOW MATHEMATICAL MODEL FOR CHANNEL NETWORKS

Based on the Preissmann implicit scheme for the one-dimensional Saint-Venant equation, the mathematical model for one-dimensional river networks and canal networks was developed and the key issues on the model were expatiated particularly in this article. This model applies the method of three-steps solution for channel-junction-channel to simulate the river networks, and the Gauss elimination method was used to calculate the sparse matrix. This model was applied to simulate the tree-type irrigation canal networks, complex looped channel networks and the Lower Columbia Slough networks. The results of water level and discharge agree with the data from the Adlul and field data. The model is proved to be robust for simulating unsteady flows in river networks with various degrees of complex structure. The calculated results show that this model is useful for engineering applications in complicated river networks. Future research was recommended to focus on setting up ecological numerical model of water quality in river networks and canal networks.     

EXPERIMENTAL INVESTIGATION OF CHARACTERISTIC FREQUENCY IN UNSTEADY HYDRAULIC BEHAVIOUR OF A LARGE HYDRAULIC TURBINE

The features of unsteady flow such as pressure variation and fluctuation in a large hydraulic turbine usually lead to the instability of operation.This article reports the recent in site investigation concerning the characteristic frequencies in pressure fluctuation,shaft torsional oscillation and structural vibration of a prototype 700 MW Francis turbine unit.The investigation was carried out for a wide load range of 200 MW-700 MW in the condition of water head 57 m-90 m.An extensive analysis of both time-history and frequency data of these unsteady hydraulic behaviours was conducted.It was observed that the pressure fluctuation in a draft tube is stronger than that in upstream flow passage.The low frequency with about one third of rotation frequency is dominative for the pressure fluctuation in part load range.Also the unsteady features of vibration of head cover and torsional oscillation of shaft exhibited the similar features.Numerical analysis showed that the vibration and oscillation are caused by vortex rope in the draft tube.In addition,a strong vibration with special characteristic frequency was observed for the head cover in middle load range.The pressure fluctuation in the draft tube with the same frequency was also recorded.Because this special vibration has appeared in the designed normal running condition,it should be avoided by carefully allocating power load in the future operation.     

EFFECT OF STREAMLINE CURVATURE AND SOME OTHER CONDITIONS ON THE TURBULENT STRUCTURES IN THE OTHER REGION OF AN OBSTACLE

ＥＦＦＥＣＴＯＦＳＴＲＥＡＭＬＩＮＥＣＵＲＶＡＴＵＲＥＡＮＤＳＯＭＥＯＴＨＥＲＣＯＮＤＩＴＩＯＮＳＯＮＴＨＥＴＵＲＢＵＬＥＮＴＳＴＲＵＣＴＵＲＥＳＩＮＴＨＥＯＴＨＥＲＲＥＧＩＯＮＯＦＡＮＯＢＳＴＡＣＬＥＬｉｕＳｈｉ－ｈｅ（ＷｕｈａｎＵｎｉｖｅｒｓｉｔ...     

THE EFFECTS OF PHYSIOLOGICAL FLOW WAVEFORM ON WALL SHEAR STRESS IN CAROTID BIFURCATION MODEL

Numerical models of carotid bifurcation were constructed using a combination of tuning-fork bifurcation and straight or curved common carotid. The different inlet velocity profiles of the common carotid were generated for Bloch flow waveform and Holdsworth flow waveform, respectively. The effects of the different flow waveform for the common carotid on Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) of carotid bifurcation were studied by CFD method. The results show that the physiological flow waveform of curved common carotid has a significant effect on OSI. In particular, the OSI on the outer walls of carotid sinus and external carotid becomes higher in the inward-curved common carotid for Holdsworth flow waveform. But, in both cases of low WSS and high OSI, the effects of flow waveforms are smaller than those of the curved common carotid. The study reveals that the exact knowledge of the physiological flow waveform, vascular geometry and inlet velocity profile is important for hemodynamic numerical simulation of artery bifurcation.     

NUMERICAL INVESTIGATION OF THREE-DIMENSIONAL FLOW AND BED SHEAR STRESS DISTRIBUTION AROUND THE SPAN SHOULDER OF PIPELINE

1 .　INTRODUCTIONWhena pipelineis placedonanerodibleseabed ,freespanmaydevelopastheresultoflocalscourunderthepipeline .Oneofthemostimpor tantissuesinpipelinestabilitydesignistheevalua tionofthefreespanlengthandtherateatwhichthefreespandevelopsalongthespandirectionduetothescour .Bothfreespanlengthandtherateofscourdevelopmentdependonflowconditionsaroundthespanshoulders.Sincemostofthescourinvestigationsintheopenliteraturewereonthescourdepthorscourdevelopmentinthe perpendiculardirectionofpipe…     

NUMERICAL SIMULATION AND EXPERIMENTAL INVESTIGATION OF THE GUIDE-VANE FLOW AND THE INFLUENCE FROM THE LEAKAGE FLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＩｔｉｓｗｅｌｌｋｎｏｗｎｔｈａｔｔｈｅｄｅｖｅｌｏｐｍｅｎｔｏｆｈｙ ｄｒａｕｌｉｃｔｕｒｂｉｎｅｉｓｆｏｒｔｈｅｂｅｓｔｈｙｄｒａｕｌｉｃｅｆｆｉｃｉｅｎｃｙａｎｄｓｔａｂｉｌｉｔｙｉｎｏｐｅｒａｔｉｏｎ .Ｔｈｅｓｔａｂｉｌｉｔｙｏｆｈｙ ｄｒａｕｌｉｃｔｕｒｂｉｎｅａｎｄｉｔｓ ｐｅｒｆｏｒｍａｎｃｅｏｆｃａｖｉｔａｔｉｏｎｅｒｏｓｉｏｎａｒｅｃｌｏｓｅｌｙｒｅｌａｔｅｄｔｏｔｈｅｆｌｕｉｄｆｌｏｗｉｎｔｕｒ ｂｉｎｅｃａｓｉｎｇ ,ｓｔａｙｖａｎｅａｎｄｇｕｉｄｅ…     

PRESSURE-VELOCITY JOINT MEASUREMENTS OF A WALL-BOUNDED TURBULENT SHEAR FLOW

1. INTRODUCTION The large-scale vortical structures characterizing unsteady behavior of turbulent shear flows have received extensive attention. Understanding the large-scale vortical structures embedded in turbulent shear flows, which consist of various-…