NUMERICAL PREDICTION OF THREE DIMENSIONAL HIGHLYTURBULENT FLOW WITH FREE SURFACES

ＮＵＭＥＲＩＣＡＬＰＲＥＤＩＣＴＩＯＮＯＦＴＨＲＥＥＤＩＭＥＮＳＩＯＮＡＬＨＩＧＨＬＹＴＵＲＢＵＬＥＮＴＦＬＯＷＷＩＴＨＦＲＥＥＳＵＲＦＡＣＥＳ￥ＭａＦｕ－ｘｉ（ＮｏｒｔｈＣｈｉｎａＩｎｓｔｉｔｕｔｅｏｆＷａｔｅｒＣｏｎｓｅｒｖａｎｃｙａｎｄＨｙｄｒ...     

SIMULATION OF STRONG TURBULENCE FLOW WITH FREE SURFACE INCLUDING THE EFFECTS OF STREAMLINE CURVATURE

This paper is concerned with a mathematical model for two-dimensional strong turbulence flow with free surface including the effects of streamline curvature in orthogonal curvilinear coordinate system, with which the characteristics of the turbulence flow field on the ogee spillway was numerical simulated. In the numerical simulation, the flow control equations in orthogonal curvilinear coordinate system were discretized by the finite volume method, the physical parameters（ P, U,V,K,ε,γt , etc. ） were arranged on a staggered grid, the discretized equations were solved with the SIMPLEC method, and the complex free surface was dealt with VOF method. The computed results show that the velocity fields, pressure field, shear stress distribution and kinetic energy of turbulent flow on the ogee spillway are in agreement with experimental data. This confirms that the model can be used for numerieal simulation of the turbulence flow on ogee spillway.     

NUMERICAL SIMULATION OF TURBULENT FREE SURFACE FLOW OVER OBSTRUCTION

A two-dimensional hybrid numerical model, FEM-LES-VOF, for free surface flows is proposed in this study, which is a combination of three-step Taylor-Galerkin finite element method, large eddy simulation with the Smagorinsky sub-grid model and Computational Lagrangian-Eulerian Advection Remap Volume of Fluid （CLEAR-VOF） method. The present FEM-LES-VOF model allows the fluid flows involving violent free surface and turbulence subject to complex boundary configuration to be simulated in a straightforward manner with unstructured grids in the context of finite element method. Numerical simulation of a benchmark problem of dam breaking is conducted to verify the present model. Comparisons with experimental data show that the proposed model works well and is capable of producing reliable predictions for free surface flows. Using the FEM-LES-VOF model, the free surface flow over a semi-circular obstruction is investigated. The simulation results are compared with available experimental and numerical results. Good performance of the FEM-LES-VOF model is demonstrated again. Moreover, the numerical studies show that the turbulence plays an important role in the evolution of free surface when the reflected wave propagates upstream during the fluid flow passing the submerged obstacle.     

LARGE EDDY SIMULATION OF FREE SURFACE TURBULENT CHANNEL FLOW WITH HEAT TRANSFER

1. INTRODUCTIONFreesurface turbulent flow exists widely in engineering. Due to difficulties in measurement and simulation, very little has been understood about the structures and transport mechanism of turbulence near the freesurface. Komori and Ueda…     

NUMERICAL SIMULATION OF MOVING SCOUR BOUNDARY AND TURBULENCE FLOW AROUND SUBMARINE PIPELINES

A two dimensional vertical mathematical model is proposed in this paper for simulating the equilibrium profile of local scour around submarine pipelines. The current model is composed of a new k-ε turbulence model, fitting moving boundary with pre-meshed grid lines and incipient criterion of shear stress for sediments. Employing the proposed model, an instance is carried out numerically and compared with experiments. The calculation results agree well with the experiments. It shows that the improved two equation turbulence model, adopted in this paper is appropriate to simulating the turbulent flow ficld around submarine pipelines, fitting moving boundary with pre-mcshed grid lines method is efficient for moving boundary problems in a multiply connected domain and the stability evaluation method for seabed with critical shear stress based on log-wall law is a reliable choice.     

NUMERICAL SIMULATION OF A TWO-DIMENSIONAL SQUARE MOVING NEAR FREE SURFACE

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｂｏｄｙｍｏｖｉｎｇｎｅａｒｔｈｅｆｒｅｅｓｕｒｆａｃｅｅｘｉｓｔｓｗｉｄｅｌｙｉｎｔｈｅｖａｒｉｏｕｓｆｉｅｌｄｓｏｆｃｏｎｅｅｒｎｉｎｇｆｌｕｉｄｍｏｔｉｏｎｓ,ｓｕｃｈａｓｎａｖａｌａｎｄｏｃｅａｎｅｎｇｉｎｅｅｒｉｎｇ ,ｃｏａｓｔａｌｅｎｇｉｎｅｅｒｉｎｇａｎｄｗａｔｅｒｅｎｔｒｙ .Ｔｈｉｓｐｈｅｎｏｍｅｎｏｎｈａｓｂｅｅｎａｆｏｃｕｓｉｎｈｙｄｒｏｄｙｎａｍｉｃｓａｌｌａｌｏｎｇ .Ｄｅａｌｉｎｇｗｉｔｈｔｈｅｓｅｐｒｏｂｌｅｍｓｉｓｄｉｆｆｉｃｕｌｔｂ…     

NUMERICAL STUDY OF THE INFLUENCE OF SURFACE ROUGHNESS OF CYLINDER ON FLOW STRUCTURE

1.　INTRODUCTIONThe quietness is an important mark for the behavior of the submarine,so to decreasethe noise of the submarine becomes more and more important.As engine noise and othernoises have been reduced in these days,the interior noise levels in many submarine applica-tions are significantly affected by the water noise in the case of a submarine athigh cruisingspeed.The main sources of water noise are as follows:( 1 ) pressure fluctuations in the tur-bulent boundary layer;( 2 ) turbul…     

NUMERICAL SIMULATION FOR THE STEPPED SPILLWAY OVERFLOW WITH TURBULENCE MODEL

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｓｔｅｐｐｅｄｓｐｉｌｌｗａｙｈａｄｂｅｅｎｕｓｅｄａｔｔｈｅｂｅｇｉｎｎｉｎｇｏｆｔｗｅｎｔｙｃｅｎｔｕｒｙ[1 ] .Ｉｎ 1 971 ,Ｅｓｓｅｒｙｅｔａｌ.[2 ] ｃｏｎｄｕｃｔｅｄａｍｏｄｅｌｔｅｓｔｆｏｒｔｈｅｄｅｓｉｇｎｏｆ     

SIMULATION OF SEDIMENT DEPOSITION IN A CAVITY WITH FREE SURFACE

Studies of the flow and sediment movement in a cavity with free surface were mostly limited to physical modeling experiments. In this study, the sediment movement is characterized in detail using a 3-D turbulent numerical model. To close the Reynolds equations, the standard k-ε model is employed. The VOF method is adopted to capture the time varying free surface and the porosity method is introduced to deal with the irregular boundary and the varying bed deformation. The computation results agree well with the experimental data in major aspects such as the vertical distribution of the sediment concentration and the deposition topography in the cavity. The comparisons show that this model can well predict the flow structure and the sediment movement and also the river bed deformation in a cavity.     

THE MACCORMACK SCHEME AND THE BOUNDARY-FITTED COORDINATE SYSTEM FOR NUMERICAL SIMULATION OF SUPER CRITICAL FREE SURFACE FLOWS

1. INTRODUCTIONOpen channels carrying supercritical flows are commonly used in hydraulic engineering. Man-made structures such as spillway chutes, conveyance channels, sewer systems, and outlet works are some typical examples. Similarly, supercritical flo…     

NUMERICAL SIMULATION OF THE TURBULENT FLUID FLOW AND PREDICTION OF INCIPIENT CAVITATION NUMBER ON ISOLATED SURFACE TRIANGULAR PROTRUSION

ＮＵＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＯＦＴＨＥＴＵＲＢＵＬＥＮＴＦＬＵＩＤＦＬＯＷＡＮＤＰＲＥＤＩＣＴＩＯＮＯＦＩＮＣＩＰＩＥＮＴＣＡＶＩＴＡＴＩＯＮＮＵＭＢＥＲＯＮＩＳＯＬＡＴＥＤＳＵＲＦＡＣＥＴＲＩＡＮＧＵＬＡＲＰＲＯＴＲＵＳＩＯＮ￥ＲｅｎＢｉ...     

NUMERICAL SIMULATION AND MEASUREMENT OF TURBULENT JET WITH FREE SURFACE

1.INTRODUCTIONTheturbulentjetwithafreesurfacehasalotofapplicationsinhydraulic,environmenalandnavalengineering.Forexample,thesubmergedjetflowisdesignedasawateracceleratortotransPOrtlogsinreservoir.Specially,thejetflowinteractingwiththefreesurfaceplaysanimportantroleforalongdistancewakebehindashipLij.AnthonyandMadniahavemeasuredthevelocityandReynoldsstressdistributions,etc.TheirexperimentalresultsshowedthatReynoldsstresshasastrongnon--homogeneouscharacternearthefreesurface.Inthepartofnum…     

THREE-DIMENSIONAL TURBULENCE NUMERICAL SIMULATION OF A STEPPED SPILLWAY OVERFLOW

In this paper, the κ-ε two-equation turbulence model was used to simulate the three-dimensional turbulent flow of the stepped spillway at the Yubeishan reservoir. In order to solve the curved free water surface and to handle the complex boundary conditions, the fractional Volume Of Fluid (VOF) model that is applicable to the solution of the stratified two-phase flow was intorduced to the κ-ε turbulence model and the unstructured grid was used for the discretization of the irregular simulation domain. By these methods, the turbulent flow field of the stepped spillway was simulated successfully.The location of the free surface along the spillway, the magnitude and distribution of the velocity, the pressure distribution on the step surface, the turbulence kinetic energy and turbulence dissipation rate were obtained by simulation. The changes and distributions of these characteristics along the width of the spillway were also obtained. The energy dissipation ratio of the stepped spillway was calculated according to the upstream and downstream water depth and velocities.     

THE STRUCTURE AND SCALE EFFECT OF WALL TURBULENT FLOW

In this paper the structure and scale effect of wall turbulence are investigated.Thecharacteristics of the turbulence structure in the wall region is described.The fact that the turbu-lence in whole flow field is controlled mainly by the structure of wall turbulence is demonstrat-ed.Discussion is concentrated on the scale effects of the streak structure,the vortex structureand the bursting frequency.     

THREE-DIMENSIONAL TURBULENCE NUMERICAL SIMULATION OF A STEPPED SPILLWAY OVERFLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅａｐｐｌｉｃａｔｉｏｎｏｆｔｈｅｓｔｅｐｐｅｄｓｐｉｌｌｗａｙｈａｓｈａｄａｌｏｎｇｈｉｓｔｏｒｙ .Ｔｈｅ ｐｈｙｓｉｃａｌｍｏｄｅｌｔｅｓｔｓｔｕｄｙｏｆｔｈｅｓｔｅｐｐｅｄｓｐｉｌｌｗａｙｈａｓｂｅｅｎ ｐｅｒｆｏｒｍ     

THE NUMERICAL SIMULATION OF TWO-DIMENSIONAL OPEN CHANNEL TURBULENCE

A numerical simulation on 2-D open channel turbulence using the two-equationturbulent model(k-e model) is made.The diseretization equations of depth-averaged 2-D differ-ential equation are obtained by the control-volume formulation.Some examples including theflows in straight open channel,symmetry sudden expansion and one-side sudden expansion arecalculated by using the SIMPLE algorithm.The distributions of the flow velocity u,the kineticturbulent energy k,and the turbulent viscosity μ,etc.are obtained.The numerical calculationsindicate a good agreement with experimental data and other turbulent models calulations.     

EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FREE SURFACE VORTEX

An experimental model was set up to investigate the formation and evolution of the free surface vortex. A Particle Image Velocimetry （PIV） was used to measure the free surface vortex flow field at different development stages. Flow visualization was used to locate the vortex position and find its structure. Empirical formulas about the critical submergence and the whole field structure were obtained. It is found that the tangential velocity distribution is similar to that of the Rankine vortex and the radial velocity changes little in the vortex functional scope. Vortex starts from the free surface and gradually intensifies to air entrainment vortex. The vortex core moves during the formation and evolution of the free surface vortex. Based on the experimental model, the vortex position and structure were predicted by numerical simulation combined with a vortex model and compared with that of the experiments, which shows satisfactory agreement.     

EXPERIMENTAL RESEARCH ON EFFECT OF MAIN-FLOW SWING ON FLOW TURBULENCE STRUCTURE

It is mentioned in this paper that the adjustment of flow structure occurs when themain-flow swings.The changes of turbulence structure and flow energy loss in the indoor rivermodel are measured.The experimental data are presented for the first time for the further studyof complicated river flow structure.     

FLOW STRUCTURE AND SEDIMENT TRANSPORT WITH IMPACTS OF AQUATIC VEGETATION

Aquatic vegetation plays an important role in the flow structure of open channels and thus changes the fate and the transport of sediment. This article proposes a three-dimensional turbulence model by introducing vegetation density and drag force into the control equations of water flow in the presence of vegetation. The model was used to calculate the impacts of submerged vegetation on the vertical profiles of longitudinal flow velocities, the changes of the depth-averaged flow velocities in a compound channel with emergent vegetation in the floodplain, the removal of suspended sediment from the channels by emergent vegetation, and the bed changes around and in a vegetated island. Numerical investigations show that aquatic vegetation retards flow in the vegetation zone, reduces the sediment transport capacity, and contributes to erosion on both sides of the vegetated island. Calculated results agree well with experimental results.     

NUMERICAL SIMULATION OF STRATIFIED FLOW WITH BOTH VERTICAL TEMPERATURE GRADIENT AND VERTICAL SALINITY GRADIENT

Density stratified flow with both the vertical temperature gradient and the verti-cal salinity gradient is simulated numerically, in which turbulent terms are calculated by a sim-plified turbulence stress/flux algebraic model. The feature of stratification and turbulence is de-scribed correctly by the model. The computational results agree well with the experimental data.However, the k-e turbulence model is not so successful.