A NEW APPROACH TO THE SIMULATION OF UNSTEADY SUBCRITICAL FLOW

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

NUMERICAL ANALYSIS OF THE INFLUENCE OF THE TIP CLEARANCE FLOWS ON THE UNSTEADY CAVITATING FLOWS IN A THREE- D IMENSIONAL INDUCER

To clarify the influences of the tip clearance flows on the unsteady cavitating flow,the three-dimensional unsteady cavitating flows through both the two-dimensional cascades and the three-dimensional inducer with and without tip clearance are performed numerically.The governing equations for the compressible fluid flow with the DES turbulence model are employed with the assumption of the isentropic process of liquid phase.The evolution of cavities is represented as the source/sink of vapor phase.The basic equations in the curve linear coordinate are solved by the finite difference method.As the results of the three-dimensional cavitating flows through the two-dimensional cascades,the tip clearance flows from the pressure side to the suction side of the blade produces the tip vortex cavitation,which affects the sheet cavitation on the leading edge of the next blade and enhances the blockage effect near the casing than the flows without tip clearance.On the other hand,in the case of the three-dimensional inducer,the large backflow cavitation is observed around the inlet of the inducer,where the cavities are developed on the casing by the tip clearance flows.The large pressure gradient between the non-cavitating pressure side and the cavitating suction side enhances the tip clearance flows.The calculation considering the tip clearance reproduces the developed cavitation region similar to that of experimental visualizations.Additionally,the backflow cavitation rotates with the speed slower than the rotation speed of the inducer.Then,the rotation of backflow cavitation causes the periodic fluctuation of the outlet pressure greater than that of the inlet pressure.     

COMPUTER-AIDED ANALYSIS OF UNSTEADY PARTIALLY FILLED FLOWS IN DRAINAGE SYSTEMS

The partially filled pipeflows encountered in drainage systems belong to a family of unsteady flow problems capable of numerical solution via the method of characteristics.The defining equations in terms of flow depth,velocity and surface wave speed are developed and numerically solved by characteristic-difference method with time-lineinterpolation scheme.Boundary conditions for inflow,outflow,moving hydraulic jump and junctions are developed both experimentally and numerically.Full scale model experiments were carried out and it was consequently clarified that numerical model is capable of predicting flow characteristics in realistic drainage networks.     

ACCURATE PIPE TOP-ENTRY JUNCTION MODEL FOR STEADY AND UNSTEADY FLOWS

ＡＣＣＵＲＡＴＥ　ＰＩＰＥ　ＴＯＰ－ＥＮＴＲＹ　ＪＵＮＣＴＩＯＮ　ＭＯＤＥＬ　ＦＯＲ　ＳＴＥＡＤＹ　ＡＮＤ　ＵＮＳＴＥＡＤＹ　ＦＬＯＷＳＡＣＣＵＲＡＴＥＰＩＰＥＴＯＰ－ＥＮＴＲＹＪＵＮＣＴＩＯＮＭＯＤＥＬＦＯＲＳＴＥＡＤＹＡＮＤＵＮＳＴＥＡＤＹＦＬＯ...     

NUMERICAL SIMULATIONS OF 2D PERIODIC UNSTEADY CAVITATING FLOWS

1. INTRODUCTION Cavitation is a natural phenomenon especially existing in liquids. A cavitating flow generally involves a large number of vapor structures such as bubbles or vortices which are convecting downstream. When they reach high pressure zones, th…     

NUMERICAL SIMULATION OF LEVEE BREACH FLOWS UNDER COMPLEX BOUNDARY CONDITIONS

Levee or dam failure can cause a significant disaster in most cases. A good prediction of the flood process especially in a real complex terrain is necessary for working out emergency plans for levee or dam breaches. Numerical simulations of levee or dam breach flow were carried out often with constant flow parameters and in relatively simple channels rather than in natural rivers with complex boundaries. This article presents our dedicated studies on the 2-D numerical model of levee or dam breach hydraulics with finite difference schemes. The good performance of the model is demonstrated by comparisons with the theoretical solution of an idealized dam-break flow over a frictionless flat rectangular channel. The model is also validated through its stability and conservation properties. The model is applied to simulate the flood propagation under complex boundary conditions, and the unsteady flood process in a river and in the dry floodplain with a complex bed terrain simultaneously. Furthermore, with respect to engineering practice, the numerical solutions can give special guidance to the effects of parameters such as the flood depth at different sites and the inundated area at different time periods after the levee breach and the travel time of the flood waves, which may be very important for practicing engineers in an efficient flood management.     

A SPLIT-CHARACTERISTIC FINITE ELEMENT MODEL FOR 1-D UNSTEADY FLOWS

An efficient and accurate solution algorithm was proposed for 1-D unsteady flow problems widely existing in hydraulic engineering. Based on the split-characteristic finite element method, the numerical model with the Saint-Venant equations of 1-D unsteady flows was established. The assembled finite element equations were solved with the tri-diagonal matrix algorithm. In the semi-implicit and explicit scheme, the critical time step of the method was dependent on the space step and flow velocity, not on the wave celerity. The method was used to eliminate the restriction due to the wave celerity for the computational analysis of unsteady open-channel flows. The model was verified by the experimental data and theoretical solution and also applied to the simulation of the flow in practical river networks. It shows that the numerical method has high efficiency and accuracy and can be used to simulate 1-D steady flows, and unsteady flows with shock waves or flood waves. Compared with other numerical methods, the algorithm of this method is simpler with higher accuracy, less dissipation, higher computation efficiency and less computer storage.     

STUDY ON FLOWS THROUGH CENTRIFUGAL PUMP IMPELLER BY TURBULENT SIMULATION

A finite volume numerical method is presented for simulating internal tur-bulent flows on the blade-to-blade surface through a centrifugal pump impeller, in which, a mesh in body-fitted coordinates is generated for the computation. In detail, the SIM-PLEC algorithm is utilized for solving governing equations of incompressible viscous/turbulent flows through the pump impeller. The K-ε turbulence model is adopted to describe the turbulent flow process. Some worthwhile simulated results are presented.     

DIRECT NUMERICAL SIMULATION OF PARTICULATE FLOWS

1 .　INTRODUCTIONParticulateflowsofsolidsinfluidshavebeenwidelyusedfordifferentpurposesinindustry ,suchassedimentingandfluidizedsuspensions ,lubricat edtransportandhydraulicfracturingofhyfrocar bonreservoirs,etc .Inthepast,particulateflowswithmany particlesaremostlynumericallysimu latedusingapproximatemethods ,whichincludesimulationsbasedonthepotentialflow ,theStokesflow ,and point particleapproximations[1] .Thecomputationsareallsimplifyiedbyignoringsomepossiblyimportanteffects .Thedistri…     

NUMERICAL SIMULATION OF THE FLOW PATTERNS OF YUQIAO RESERVOIR

In this paper the slot method is used in the computation of 2-dimensional flow withtransient boundary.The slot located inside the computation zone is placed in each space grid,parallel to both X and Y axes.Combined with the operator splitting method,the numerical simu-lation of the flow patterns of Yuqiao Reservior is made.The calculated results are in good agree-ment with observed data.     

潇湘水库入库径流随机模拟

针对潇湘水库的实测入库径流资料，采用了数学模型与模拟模型相结合的随机动态规划模拟模型，对萧湘水库的年径流的模拟采用了一阶自回归模型，对于月径流的模拟，则采用了相关解集模型来模拟，通过对水库入库径流的模拟，得到水库的入库径流过程。     

NUMERICAL SIMULATION OF TRANSIENT FLOW AROUND A SHIP IN UNSTEADY BERTHING MOTION

Ship berthing is a specific maneuver operation. The flow around a berthing ship and the forces acting on the hull are quite different from those for a ship in normal navigation. By solving the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations, the transient flow field around a ship undergoing unsteady lateral motion is simulated and the varying lateral hydrodynamic force acting on the hull is evaluated in this article. The numerical results obtained with different turbulence models are analyzed and compared with experimental results and other numerical results published in literature, and a turbulence model more suitable for simulation of the viscous flow around a ship undergoing unsteady berthing is determined.     

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 ANALYSIS OF THE UNSTEADY FORCE IN INSECT FORWARD FLIGHT

1. INTRODUCTION Although the quasi-steady analysis provides a simple framework for quantitative prediction of the forces in insect flight, the predicted forces and power requirements of insects in hovering or forward flight cannot prove that insects use t…     

3D NUMERICAL SIMULATION ON WATER AND AIR TWO-PHASE FLOWS OF THE STEPS AND FLARING GATE PIER

1. INTRODUCTION Withtheincreasingofthenumberofthehigh damandtheunitdischargethroughthespillway, theexpertsandscholarshavepaidmoreattention tothemethodofenergydissipation.Asetofphys icalexperimentalresearchonsteppedspillwayhas beencarriedout[1,2].Innumericalsimulation,Un amietal.[3]gavethetwo dimensionnumerical modelofspillwayflow,andSongetal.[4]calculat edthefreesurfaceflowoverspillway.Liuetal.[5] simulatedthewaterflowoveraweirwith2Dk ε turbulentmodel.Xuetal.[6]calculatedthe3Dcompl…     

NUMERICAL SIMULATION OF THE EFFECT OF FILLET FORMS ON APPENDAGE－BODY JUNCTION FLOW

ＮＵＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＯＦＴＨＥＥＦＦＥＣＴＯＦＦＩＬＬＥＴＦＯＲＭＳＯＮＡＰＰＥＮＤＡＧＥ－ＢＯＤＹＪＵＮＣＴＩＯＮＦＬＯＷＬｉＤｉｎｇ；ＺｈｏｕＬｉａｎ－ｄｉ（ＣｈｉｎａＳｈｉｐＳｃｉｅｎｔｉｆｉｃＲｅｓｅａｒｃｈＣｅｎｔｅｒＰ．...     

NUMERICAL SIMULATION OF STRESS-INDUCED SECONDARY FLOWS WITH HYBRID FINITE ANALYTIC METHOD

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｔｕｒｂｕｌｅｎｔｓｔｒｕｃｔｕｒｅｓｉｎｎｏｎ ｃｉｒｃｕｌａｒｄｕｃｔｓａｎｄｏｐｅｎｃｈａｎｎｅｌｓａｒｅｃｈａｒａｃｔｅｒｉｚｅｄｂｙｌｏｎｇｉｔｕｄｉ ｎａｌｖｏｒｔｉｃｅｓ .Ｔｈｅｓｅｖｏｒｔｉｃｅｓａｒｅｔｈ     

RESEARCH ON IMPROVED CUT-OFF NEGATIVE PRESSURE METHOD FOR UNSTEADY SEEPAGE FLOW WITH FREE SURFACE

1.INTRODUCTIONThe analysis of seepage flow with free surfaceis often required in geotechnical engineering andhydraulic engineering.It is complex since the freesurface is unknown prior to analysis,namely thestudy areais unknown before computation.The so-lution of free surface substantially belongs to non-linear and free boundary problem.At present,twokinds of finite element analysis method have beenpresented for solving the problem.One is iterativemethod[1]with mesh changedinstantly andthe…     

RESEARCH ON THE MIXING LAYER OF FIBER SUSPENSIONS AND DIRECT SIMULATION ON THE MOTION OF CYLINDRICAL PARTICLES

The mixing layer of fiber suspensions was simulated numerically with the spectral method and the fibers in the flow were traced individually with calculation. The corresponding experiments were made. The results show that the Stokes number of particles is the key parameter to determine the spatial distribution of fibers and the coherent structures control the orientation of fibers. Direct simulations of the motion of cylindrical particles were carried out via lattice Boltzmann method. It is found that the aspect ratio of particles has significant effects on the translation and rotation of the cylindrical particles. A new lattice Boltzmann method which is convenient to deal with the curved boundary is proposed.     

NUMERICAL SIMULATION OF ATOMIZATION RAINFALL AND THE GENERATED FLOW ON A SLOPE

This article studies the atomization rainfall and the generated flow on a slope by numerical simulations.The atomization rainfall is simulated by a unified model for splash droplets and a suspended mist,and the distribution of the diameter of splash rain drops is analyzed.The slope runoff generated by the atomization rainfall is simulated by a depth-averaged 2-D model,and the localization of the rainfall intensity in space is specially considered.The simulation results show that:(1) the median rain size of the atomization rainfall increases in the longitudinal direction at first,then monotonously decreases,and the maximum value is taken at the longitudinal position not in consistent with the position where the maximum rain intensity is taken.In the lateral direction the median rain size monotonously decreases,(2) since the atomization rainfall is distributed in a strongly localized area,it takes a longer time for its runoff yield to reach a steady state than that in the natural rainfall,the variation ranges of the water depth and the velocity in the longitudinal and lateral directions are larger than those in the natural rainfall.