NUMERICAL SIMULATION OF FLOW OVER TWO CIRCULAR CYLINDERS IN TANDEM ARRANGEMENT

In this article,the 2-D unsteady viscous flow around two circular cylinders in a tandem arrangement is numerically simulated in order to study the characteristics of the flow in both laminar and turbulent regimes.The method applied alternatively is based on the finite volume method on a Cartesian-staggered grid.The great source term technique is employed to identify the cylinders placed in the flow field.To apply the boundary conditions,the ghost-cell technique is used.The implemented computational method is firstly validated through simulation of laminar and turbulent flows around a fixed circular cylinder.Finally,the flow around two circular cylinders in a tandem arrangement is simulated and analyzed.The flow visualization parameters,the Strouhal numbers,and drag and lift coefficients are comprehensively presented and compared for different cases in order to reveal the effect of the Reynolds number and gap spacing on the behavior of the flow.The obtained results have shown two completely distinct flow characteristics in laminar and turbulent regimes.     

NUMERICAL SIMULATION OF FLOW OVER TWO SIDE-BY-SIDE CIRCULAR CYLINDERS

In the present paper, the unsteady, viscous, incompressible and 2-D flow around two side-by-side circular cylinders was simulated using a Cartesian-staggered grid finite volume based method. A great-source term technique was employed to identify the solid bodies (cylinders) located in the flow field and boundary conditions were enforced by applying the ghost-cell technique. Finally, the characteristics of the flow around two side-by-side cylinders were comprehensively obtained through several computational simulations. The computational simulations were performed for different transverse gap ratios (1.5≤T/D≤4) in laminar (Re=100,200) and turbulent (Re=104) regimes, where T and D are the distance between the centers of cylinders and the diameter of cylinders, respectively. The Reynolds number is based on the diameter of cylinders,D. The pressure field and vorticity distributions along with the associated streamlines and the time histories of hydrodynamic forces were also calculated and analyzed for different gap ratios. Generally, different flow patterns were observed as the gap ratio and Reynolds number varied. Accordingly, the hydrodynamic forces showed irregular variations for small gaps while they took a regular pattern at higher spacing ratios.     

EXPERIMENTAL INVESTIGATION ON SOUND SPEED PROPAGATING THROUGH HIGH SPEED AERATED FLOW IN OPEN CHANNEL

An experiment concerning the sound propaga-tion in aerated open channel flow was designed and conductedin a variable slope chute. The acquisition of sound data wasdone by the hydro-phones installed into the bottom wall of thechute. The data were analyzed and processed by the tape re-corder and a 3562A analyzer. The primary experimetal resultsindicated that the sound speed in aerated flow is varied with the air concentration and highly lower than each of the soundspeed in pure water or air. As released by the derived theoryformula, the minimum sound of 24m/s in aerated flow hap-pened when the air concentration achieved to 50%. This resultshows that the compressibility of high speed aerated flowshould be considered when the air concentration is near to50%. A criterion of compressibility of high speed aerated flowwas also giv. En in this paper.     

GRID GENERATION AND NUMERICAL SIMULATION OF 2-D RIVER FLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｎａｔｕｒａｌｒｉｖｅｒ,ｔｈｅｓｈａｐｅｓｏｆｂｏｕｎｄａｒｉｅｓａｎｄｓｅｃ ｔｉｏｎｓａｒｅｏｆｔｅｎｉｒｒｅｇｕｌａｒ ,ｗｈｉｃｈｉｓａｄｉｆｆｉｃｕｌｔｐｒｏｂｌｅｍｆｏｒｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎ .Ｔｏｓｏｌｖｅｔｈｉｓｐｒｏｂｌｅｍ ,ａｃｏｏｒｄｉ ｎａｔｅｔｒａｎｓｆｏｒｍａｔｉｏｎｍｅｔｈｏｄｉｓｏｆｔｅｎｕｓｅｄｔｏｔｒａｎｓｆｏｒｍｔｈｅｉｒｒｅｇｕｌａｒｒｅｇｉｏｎｉｎｔｈｅｐｈｙｓｉｃａｌｐｌａｎｅ(Ｘ ,Ｙ)ｔｏｔｈｅｒｅｇｕｌａ…     

THE OPTIMAL MOTION OF TWO-DIMENSIONAL UNDULATING PLATE SWIMMING IN FLUID FLOW

The optimum shape of a two-dimensional undulatory plate in its motion in fluid flow is analyzed and the physical parameters(the thrust and the power)are calculated by the boundary element method.With the commonly used Lagrange multiplier method,only a saddle point of the optimum solution can be obtained,but not the solution itself due to the singularity of the problem.To eliminate the singularity,a method is proposed by adding an amplitude constraint.The new method is a generalization of that proposed by Wu,and it can be applied to more complex cases.The optimum shape of the linearly varying amplitude motion is studied in detail.It is shown that both the maximum and the minimum solutions exist when the frequency is higher than a critical value.For a high frequency,the maximum efficient motion with a large amplitude at the leading edge and a small amplitude at the trailing edge induces a large leading edge suction force.As the frequency decreases,the leading edge suction force decreases to a minimum and then increases.For high wavenumbers,there exists an optimum frequency with the maximum efficiency.High efficiency holds over a large range of frequency.The optimum efficiency increases as the wavenumber increases.The increase of the wavenumber can also reduce the leading edge suction force.The optimization method can also be applied to a quadratically varying amplitude motion.It is found that the optimum efficiency is larger than that for the linearly varying amplitude motion.However,the additional efficiency is relatively small,especially as the original efficiency is already high enough.     

AN INVERSE PROBLEM OF WATER WAVE GENERATION IN A WAVE TANK

ＡＮＩＮＶＥＲＳＥＰＲＯＢＬＥＭＯＦＷＡＴＥＲＷＡＶＥＧＥＮＥＲＡＴＩＯＮＩＮＡＷＡＶＥＴＡＮＫＭｉａｏＧｕｏ－ｐｉｎｇ；ＹｏｕＹｕｎ－ｘｉａｎｇ；ＬｉｕＹｉｎｇ－ｚｈｏｎｇ（ＳｈａｎｇｈａｉＪａｏＴｏｎｇＵｎｉｖｅｒｓｉｔｙＳｈａｎｇｈａｉ２０００...     

NUMERICAL SIMULATION OF GAS-WATER LEAKAGE FLOW IN A TWO LAYERED COALBED SYSTEM

For a two layered coalbed system in possession of the slightly permeable interlayer, a mathematical model was established to describe the methane and water flows between coal seams and the internal migration and the distribution of fluids in a slightly permeable interlayer. Meanwhile, this model has included the potential effect of matrix shrinkage associated with desorption on the coal permeability. The numerical results were obtained by the finite difference method, and then the production forecasts for the two layered coalbed system were conducted in combination with the geological data of a certain area in the Qinshui Basin. Through analyzing the internal migration and distribution of fluids in the slightly permeable interlayer and its effect on the coalbed methane well production, the results indicate that the prediction of the gas production rate and the cumulative gas production will be higher if the permeability of the interlayer is neglected. Furthermore, it is also found that the matrix shrinkage could produce an effect on the coal permeability, thus affecting the production performance.     

ON THE MECHANISM OF DRAG REDUCTION IN HIGH CONCENTRATION NON-HOMOGENEOUS PIPE FLOW

In this paper a method for calculating the resistance force in high concentrationnon-homogeneous pipe flow is suggested.Comparing with experiment,it is shown that the theo-retical results are in good agreement with the experimental ones.     

SIMULATION OF THE TWO PHASE FLOW OF DROPLET IMPINGEMENT ON LIQUID FILM BY THE LATTICE BOLTZMANN METHOD

A Lattice Boltzmann Method (LBM) with two-distribution functions is employed for simulating the two-phase flow induced by a liquid droplet impinging onto the film of the same liquid on solid surface.The model is suitable for solution of twophase flow problem at high density and viscosity ratios of liquid to vapor and phase transition between liquid and its vapor.The roles of the vapor flow,the density ratio of liquid to vapor and the surface tension of the droplet in the splashing formation are discussed.It is concluded that the vapour flow induced by the droplet fall and splash in the whole impinging process may affect remarkably the splash behaviour.For the case of large density ratio of liquid to vapor a crown may engender after the droplet collides with the film.However,for the case of small density ratio of liquid to vapor a "bell" like splash may be observed.     

SIMULATION OF OIL-WATER TWO PHASE FLOW AND SEPARATION BEHAVIORS IN COMBINED T JUNCTIONS

The combined T junctions used for the oil-water separation have the advantages of compactness in structure,consistency in effects and economy in cost.The mixture turbulence model and the Eulerian multi-fluid model are used to simulate the flow and phase distribution in the combined T junctions.The effects of structural parameters such as the branched pipe interval and height on the flow distribution and the separation behaviors are studied.The results show that the combined T junctions under fixed inlet and outlet boundary conditions form a single hydraulic equilibrium system in which the fluid energy distributes freely till a balance is achieved.The split-flow promotes the separation of the immiscible oil and the water.The separation efficiency increases with the increase of the branched pipe interval and changes slightly with the increase of the branched pipe height.The structural change of the combined T junctions may change the flow direction in the branched pipes.Simulation results can provide some guidance for the design of the combined T junctions as one kind of oil-water separator.     

A NON LINEAR ANALYSIS OF TWO PHASE FLOW INSTA BILITY IN PARALLEL CHANNELS OF A BOILING SYSTEM

１．　ＩＮＴＲＯＤＵＣＴＩＯＮＴｗｏｐｈａｓｅｆｌｏｗｉｎｓｔａｂｉｌｉｔｙａｒｅｏｆｔｅｎｅｎｃｏｕｎｔｅｒｅｄｉｎａｗｉｄｅｒａｎｇｅｏｆｅｎｇｉｎｅｅｒｉｎｇｓｙｓｔｅｍｓ，ｓｕｃｈａｓｎｕｃｌｅａｒｒｅａｃｔｏｒｓ，ｓｔｅａｍｐｏｗｅｒｐｌａｎｔｓ，ｓｐｅｃｉａｌｈｅａｔｅｘｃｈａｎｇｅｒｓ，ｓｔｅａｍｇｅｎｅｒａｔｏｒｓ，ｃｈｅｍｉｃａｌｉｎｄｕｓｔｒｙｅｑｕｉｐｍｅｎｔｓａｎｄｓｏｏｎ［１］［２］　．Ｉｎｔｈｅｓｅｓｙｓｔｅｍｓ，ｔｗｏｐｈａｓｅｆｌｏｗｉｎｓｔａｂｉｌｉｔ…     

THE FRICTIONAL RESISTANCE CHARACTERISTICS OF GAS LIQUID TWO PHASE FLOW IN HELICAL COILED TUBES

1.　INTRODUCTIONThe equipments with helical-coiled tubes have been widely applied in industry,such asnylon production,boiler,special heat exchangers,nuclear power station and so on.Manyauthors have been done lots of experimental studies on frictional resistance characteristics ofgas liquid two-phase flow in helical-coiled tubes[1 ] [2 ] .But,there has been rate related treat-mentby means of dimension analysis andπtheorem.The experimentof frictional resistance characteristics of gas-liqui…     

A FLUID MECHANICS MODEL OF TISSUE FLUID FLOW IN LIMB CONNECTIVE TISSUE-A MECHANISM OF ACUPUNCTURE SIGNAL TRANSMISSION

This article explores the mechanisms of acupuncture meridians by determining characteristics of the tissue fluid flow in the connective tissue along meridians. Based on deep dissection of acupoints on the upper and lower limbs of the human body and micro and macro observation and measurement, a mathematical model of the flow of tissue fluid in interosseous membranes is constructed. It is shown that the signal transmission along acupuncture meridians may be determined by unique anatomical and physiological factors that govern the flow of tissue fluid in the connective tissue and involve mast cell degranulation. Our results provide a preliminary explanation of the phenomenon of the “de qi” sensation and the mechanism of acupuncture signal transmission along acupuncture meridians.     

AN EXPERIMENTAL INVESTIGATION OF PRESSURE AND CAVITATION CHARACTERISTICS OF HIGH VELOCITY FLOW OVER A CYLINDRICAL PROTRUSION IN THE PRESENCE AND ABSENCE OF AERATION

This article experimentally investigated the pressure and cavitation characteristics of high velocity flow over a surface irregularity with and without aeration in a non-circulating water tunnel system. The surface irregularity is a cylindrical protrusion made of stainless steel of 6 mm diameter and 2 mm height. Pressures with and without aeration were measured with MPX400D pressure transducers and real-timely acquired by a SINOCERA YE6263 data acquisition system. Variations in flow regimes with and without aeration were observed. Pressure profiles and their variations with air concentration upper and lower cylindrical protrusion on the invert and obvert walls were determined. Variations of cavitation number with air concentration lower cylindrical protrusion were analyzed. Also, cavitation numbers in the presence and absence of aeration were compared.     

FINITE ELEMENT ANALYSIS OF THE FLOW INDUCED BY ROTATING BLADES IN AN INCOMPRESSIBLE VISCOUS FLUID

Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data.     

NUMERICAL STUDY OF WALL WETTABILITIES AND TOPOGRAPHY ON DRAG REDUCTION EFFECT IN MICRO-CHANNEL FLOW BY LATTICE BOLTZMANN METHOD

The dynamics of two-phase flows with a constant driving force inside a micro-channel is studied by using the Lattice Boltzmann Method (LBM) and the Shan-Chen multiphase model in this article. Flow regimes under different wall wettabilities and over smooth and grooved geometric surfaces are investigated. It is found that flow behaviors are strongly affected by the wall wettability and topography. Our results show that the LBM is efficient and accurate, and has very good application prospect in the study of drag reduction of microscopic seepage of reservoir.     

A LDA STUDY OF THE TURBULENT FLOW FIELD IN A BAFFLED VESSEL GENERATED BY A PTD AND A PTU

1.　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｐｉｔｃｈｅｄｂｌａｄｅｔｕｒｂｉｎｅｉｍｐｅｌｌｅｒｉｓｅｓｐｅｃｉａｌｌｙｅｆｆｉｃａｃｉｏｕｓｉｎｆｌｏｗｓｅｎｓｉｔｉｖｅｍｉｘｉｎｇｏｐｅｒａｔｉｏｎｓｓｕｃｈａｓｓｏｌｉｄｓｕｓｐｅｎｓｉｏｎ,ｓｏｔｈａ?..