AN APPROACH IN MODELING TWO-DIMENSIONAL PARTIALLY CAVITATING FLOW

1. INTRODUCTIONCavitation is a phenomenon that widely occurs in liquids. When the flow leads to the local pressure below the saturation vapor pressure of water (the fluid medium, in our research), usually incipient cavitation firstly occurs on the solid b…     

NUMERICAL SIMULATIONS OF CAVITATING FLOWS

BRIEFINTRODUCTIONOFTHEPAPER :　Thisthesismainlyresearchesonthehydrodynamiccharacteristicsandmechanismfor 3Dcavitatingflowsaroundaxisymmetricbodies ,aswellasthe2Dcavitatingflowsaroundhydrofoils .Anewcavi tatingflowmodel,whichinvolvesviscousandmul ti phaseeffects,isestablishedintwo phaseflowcategory .Accordingtothelocalizedvariationofdensitywithinpredominantlyincompressiblewatermediumandthecharacteristicsofsoundspeedinwater vapormixture ,arelationbetweendensityandpressureisassumed ,in…     

URANS COMPUTATION OF CAVITATING FLOWS AROUND SKEWED PROPELLERS

Cavitating flows around skewed propellers are investigated numerically by means of the unsteady Reynolds Averaged Navier-Stokes (RANS) Equation method. The standard k-ε turbulence and the modified Z-G-B cavitation models are employed. A measured nominal wake is used for the inlet velocity boundary condition. Predicted cavitating evolution processes and tip cavity patterns are compared with experimental observations. In addition, the influence of the skew angles on the cavitation and unsteadiness performances of propellers operating in a non-uniform wake is also studied. Results show that the modified Z-G-B cavitation model performs better to simulate the cavitating flow cases studied in this paper. Comparisons demonstrate that the skewed propeller with a skew angle of 20 o is the best choice for a given stern wake with a assigned thrust and the minimum force fluctuations.     

APPLICATION OF QUADRATIC AND CUBIC TURBULENCE MODELS ON CAVITATING FLOWS AROUND SUBMERGED OBJECTS

Quadratic and cubic Non-Linear Eddy-Viscosity Models(NLEVMs) at low Reynolds number correction were introduced into the present Computational Fluid Dynamics(CFD) framework,to provide better numerical treatment about the anisotropic turbulence stress in cavitating flows,which have large density ratio and large-scaled swirling flow structures.The applications of these NLEVMs were carried out through a self-developed cavitation code,coupled with a cavitation model based on the transport equation of liquid phase.These NLEVMs were firstly validated by the benchmark of disk supercavity,and found able to obtain more accurate capture of the hydrodynamic properties than the linear models.One of such models was further applied on the cavitation problem of submerged vehicles.Ultimately,the supercavitating flows around an especially designed underwater vehicle were predicted using the cubic turbulence model,and its cavitation behaviors were studied.     

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…     

INTERFERENCE OF SIDE STRUT WITH THE NATURAL CAVITATING FLOWS AROUND A SUBMERGED VEHICLE IN WATER TUNNEL EXPERIMENTS

To apply the measurements of model experiment in water tunnel to the actual sailing condition,it is necessary to know accurately the strut effect and its rule.In the present work,the corresponding interferences of one-side strut and two-side strut on the natural cavitating flows around a submerged vehicle in water tunnel were investigated numerically,using the homogeneous equilibrium two-phase model coupled with a natural cavitation model.The numerical simulation results show that the strut types have distinct effects on the hydrodynamic properties.For the same given upstream velocity and downstream pressure,the existence of the strut leads to an increment of natural cavitation number,reduces the low-pressure region and depresses the pressure on the vehicle surface near the sides of strut.In the case of given cavitaiton number,the influences of the two-side strut on the drag and lift coefficients are both enhanced along with the increment of attack angle,however the influence of the one-side strut gradually gets stronger on the drag coefficient but weaker on the lift coefficient contrarily.In addition,based on the present numerical results,a correction method by introducing the sigmoidal logistic function is proposed to eliminate the interference from the foil-shaped strut.     

ASSESSMENT OF A CENTRAL DIFFERENCE FINITE VOLUME SCHEME FOR MODELING OF CAVITATING FLOWS USING PRECONDITIONED MULTIPHASE EULER EQUATIONS

A numerical treatment for the prediction of cavitating flows is presented and assessed.The algorithm uses the preconditioned multiphase Euler equations with appropriate mass transfer terms.A central difference finite volume scheme with suitable dissipation terms to account for density jumps across the cavity interface is shown to yield an effective method for solving the multiphase Euler equations.The Euler equations are utilized herein for the cavitation modeling,because some certain characteristics of cav...     

TWO MODIFICATORY K-ε TURBULENCE MODELS FOR TURBULENT SWIRLING FLOWS

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｓｔａｎｄａｒｄＫ εｔｕｒｂｕｌｅｎｃｅｍｏｄｅｌｉｓｗｉｄｅｌｙｕｓｅｄｆｏｒｐｒｅｄｉｃｔｉｎｇｔｕｒｂｕｌｅｎｔｆｌｏｗｓｉｎｅｎｇｉｎｅｅｒｉｎｇａｐ ｐｌｉｃａｔｉｏｎｓ,ａｎｄｔｈｅｅｘｐｅｒｉｅｎｃｅｕｓｉｎｇｉｔｉｎｐｒａｃｔｉｃｅｈａｓｄｅｍｏｎｓｔｒａｔｅｄｔｈａｔｉｔｉｓｓｕｃｃｅｓｓｆｕｌｉｎ ｐｒｅｄｉｃｔｉｏｎｏｆｍａｎｙｔｕｒｂｕｌｅｎｔｆｌｏｗｓ,ｅｓｐｅｃｉａｌｌｙｔｈｅｓｉｍｐｌｅｓｈｅａｒｆｌｏｗ .Ｆｏｒｆｌｏｗｓｓｕｂｊｅｃ…     

ANALYSIS OF BASSET FORCE OF PARTICLE MOTION IN TURBULENT FLOWS WITH SPECTRAL METHOD

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＷｉｔｈｔｈｅｗｉｄｅａｖａｉｌａｂｉｌｉｔｙｏｆｃｏｍｐｕｔａｔｉｏｎａｌｔｅ ｃｈｏｌｏｇｙ ,ｔｈｅｎｕｍｅｒｉｃａｌＬａｇｒａｎｇｉａｎｃｏｍｐｕｔａｔｉｏｎｆｏｒｆｌｏｗｓｉｎｖｏｌｖｉｎｇｄｉｓｐｅｒｓｅｄｓｏｌｉｄｐａｒｔｉｃｌｅｓｏｒａｉｒｂｕｂｂｌｅｈａｓｉｎｃｒｅａｓｅｄｄｒａｍａｔｉｃａｌｌｙｉｎｒｅｃｅｎｔｙｅａｒｓ .ＡｌｌｏｆｔｈｅｓｅｃｏｍｐｕｔａｔｉｏｎｓｕｓｕａｌｌｙｓｔａｒｔｅｄｗｉｔｈＬａｇｒａｎｇｉａｎｅｑｕａｔｉｏｎｏｆ ｐａｒｔ…     

EXPERIMENTAL STUDY OF 3-D TURBULENT BEND FLOWS IN OPEN CHANNEL

1.INTRODUCTION Mostnaturalflowsareturbulent,andthenat uralriversareprevalentlymeandering.Mostofthe riverbendsarethosewithnot fully developedcir culationcurrentsonly,inwhichcentralanglesfor thebendsaresmallerthan180°,even90°.These bendflowsarecharacterizedbythedevelopmentoflateralcirculationcurrentsandbythenot fully offsetsofmainflow,withobvious3Dfeatures.Soinhydraulicengineeringandnavigationengi neering,itisimportantandnecessarytoinvesti gatethe3Dturbulentcharactersofbendflow.Be causet…     

IMPROVEMENT OF BUBBLE MODEL FOR CAVITATING FLOW SIMULATIONS

In the present research,a bubble dynamics based model for cavitating flow simulations is extended to higher void fraction region for wider range of applications.The present bubble model is based on the so-called Rayleigh-Plesset equation that calculates a temporal bubble radius with the surrounding liquid pressure and is considered to be valid in an area below a certain void fraction.The solution algorithm is modified so that the Rayleigh-Plesset equation is no more solved once the bubble radius(or void fraction)reaches at a certain value till the liquid pressure recovers above the vapor pressure in order to overcome this problem.This procedure is expected to stabilize the numerical calculation.The results of simple two-dimensional flow field are presented compared with the existing bubble model.     

NUMERICAL SIMULATION OF 3-D TURBULENT FLOWS OF PLUNGE POOL AND ENERGY DISSIPATION ANALYSIS

A 3-D numerical model for simulating the complicated turbulent flows was developed and the code was made. A numerical calculation of the plunge pool of Laxiwa project in China was carried on. Those 3-D distributions of velocity,pressure on bottom wall,turbulence kinetic energy and turbulence energy dissipation rate are revealed in detail and the detailed flow patterns of plunge pool were shown. By studying on the characteristics of turbulent diffusion and energy dissipation,the calculated results show that the major turbulence and energy dissipation are taken place near the axis of water jet. The calculated results also indicated that the calculated maximum impact pressures on the bottom wall of the plunge pool have a good agreement with those obtained by physical hydraulic model test.     

NUMERICAL SIMULATIONS OF TURBULENT FLOWS PASSED THROUGH AN ORIFICE ENERGY DISSIPATOR WITHIN A FLOOD DISCHARGE TUNNEL

Numerical simulations of turbulent flows in a multiple-orifice energy dissipatorare presented.The solution procedure,based on K-ε turbulence model,is described.The Calcu-lated properties of the flows are compared with experiments and demonstrate that flow fields canbe predicted well by the procedure.     

MATHEMATICAL MODELS AND NUMERICAL SIMULATION FOR DENSE PARTICULATE FLOWS

Sedimentation of particles in inclined and vertical vessels is numerically simulated by the Eulerian two-fluid model. The numerical results show an interesting phenomenon with two circulation vortexes in a vertical vessel but one in the inclined vessel. Sensitivity tests indicate that the boundary layer effect is the key to induce this phenomenon. A numerical method based on 2D unstructured meshes is presented to solve the hard-sphere discrete particle model. Several applications show the numerical method has a good performance to simulate dense particulate flows in irregular domains without regard to element types of the mesh.     

THE SOLUTION FOR INCOMPRESSIBLE PLANE TURBULENT JET BY USING THE METHOD OF SUCCESSIVE SUBSTITUTION

Based on P. Y. Chou's theory of turbulence for incompressible viscous fluids, this paper solves the Reynolds' equations of mean motion and the equations of turbulent fluctuation simultaneously using the method of successive substitution. The comparison of the computed results for incompressible plane turbulent jet with the experimental data is reasonably good.     

AN INVESTIGATION OF TURBULENT HEAT TRANSFER IN CHANNEL FLOWS BY LARGE EDDY SIMULATION

Large Eddy Simulation (LES) of fully developed turbulent channel flow with heat transfer was performed to investigate the effects of the Reynolds number on the turbulence behavior. In the present study, the bottom wall of the channel was cooled and the top wall was heated. The Reynolds numbers, based on the central mean-velocity and the half-width of the channel, were chosen as 4000, 6000, 104 and 2×104, and the Prandtl number as 1.0. To validate our calculations, the present results were compared with available data obtained by Direct Numerical Simulation (DNS), which proves to be in good agreement with each other. To reveal the effects of the Reynolds number, some typical quantities, including the velocity fluctuations, temperature fluctuation, heat fluxes and turbulent Prandtl number, were studied.     

NUMERICAL SIMULATION OF TURBULENT FLOW THROUGH THROAT-TYPE ENERGY-DISSIPATORS

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｏｃｏｎｖｅｒｔａｄｉｖｅｒｓｉｏｎｔｕｎｎｅｌｉｎｔｏａｆｌｏｏｄｄｉｓ ｃｈａｒｇｅｔｕｎｎｅｌｃａｎｓａｖｅａｌａｒｇｅａｍｏｕｎｔｏｆｉｎｖｅｓｔｍｅｎｔ.Ｔｈｅｒｅａｒｅｍａｎｙｓｕｃｃｅｓｓｆｕｌｅｘａｍｐｌｅｓｉ     

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

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｔｕｒｂｕｌｅｎｔｓｔｒｕｃｔｕｒｅｓｉｎｎｏｎ ｃｉｒｃｕｌａｒｄｕｃｔｓａｎｄｏｐｅｎｃｈａｎｎｅｌｓａｒｅｃｈａｒａｃｔｅｒｉｚｅｄｂｙｌｏｎｇｉｔｕｄｉ ｎａｌｖｏｒｔｉｃｅｓ .Ｔｈｅｓｅｖｏｒｔｉｃｅｓａｒｅｔｈ     

A RAISED PANEL METHOD BASED ON NURBS FOR FREE-SURFACE POTENTIAL FLOWS WITH FORWARD SPEED

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＲｅｓｅｎｔｙｅａｒｓ,ＮＵＲＢＳｈａｖｅｇｏｔｗｉｄｅｓｐｒｅａｄａｃ ｃｅｐｔａｎｃｅａｎｄｐｏｐｕｌａｒｉｔｙｉｎｔｈｅＣＡＤ/ＣＡＭａｎｄｇｒａｐｈ ｉｃｓｃｏｍｍｕｎｉｔｙ .ＴｈｅｒａｐｉｄｐｒｏｌｉｆｅｒａｔｉｏｎｏｆＮＵＲＢＳｉｓｄｕｅｐａｒｔｌｙｔｏｔｈｅｉｒｅｘｃｅｌｌｅｎｔｐｒｏｐｅｒｔｉｅｓａｎｄｐａｒｔｌｙｔｏｔｈｅｉｒｉｎｃｏｒｐｏｒａｔｉｏｎｉｎｓｕｃｈｎａｔｉｏｎａｌａｎｄｉｎｔｅｒｎａｔｉｏｎａｌｓｔａｎｄａｒｄｓａｓＩＧＥＳ ,ＰＨＩＧＳ …