NUMERICAL INVESTIGATION ON OSCILLATING FLOWSPAST A HALF CIRCULAR CYLINDER ON A PLANE

l.INTRoDUCTIoNTheunsteadyflowpastabluffbodyhasreceivedagreatdealofattentionowingmainlytoitstheoreticalandpracticalsignificance.Foranoscillatingflowpastacircularcylinder,thetwoparametersgoverningthedevelopmentoftheflowaretheReynoldsnumber,de-finedbyRe=2U,R/v,WhereU,isthemaximumvelocityoftheambientflow,visthekine-maticviscosityandRistheradiusofthecircularcylinder;andtheKeulegan-Carpenternum-ber,definedasKC=U,T/2R,whereTistheoscillationperiod.Todescirbethisproblem,earlierstudiesofviscou…     

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…     

APPLICATION OF VORTEX-IN-CELL METHOD IN THE RANDOM DISCRETE VORTEX SIMULATION FOR THE SEPARATED FLOW AROUND A CIRCULAR CYLINDER

The vortex-in-cell method in the discrete vortex simulation for the separatedflow around a bluff body is discussed,Some improvements are made.The separatedflow around a circular cylinder in oscillatory flow is investigated.     

A STUDY ON THE FLOW BEHAVIOR OF AN AXISYMMETRIC LAMINAR JET

It is of great practical and theoretical importance to study the properties and flowbehavior of laminar jet,because it tightly links the physical phenomena of nonlinerity such asflow stability and transition and so forth.However,many problems and differences exist in ba-sic concepts and in understanding of stable and transitional properties and flow patterns of ax-isymmetric laminar jet.Therefore,a further study on this subject is needed to evaluate the exist-ing understandings and to find out the mechanism governing the behavior of actual axisymmetriclaminar jet flow.In this thesis,the flow behavior of axisymmetric laminar jet issuing from nozzles of severaldiameters in the direction of gravity was studied experimentally using flow visualization tech-nique in the range of Reynolds number from tens to thousands.The unstable and transitionalprocesses in the laminar jet were observed.The influence on the jet flow of different geometrycontours of jet chamber boundary was investigated.Some new flow phenomena were discoveredwhich gave deeper understanding of flow patterns and their dependent factors in low Reynoldsnumber axisymmetric laminar jet.A theoretical model to describe the variation of the axisym-metric laminar jet length influenced by the weak density difference is proposed based on the ex-perimental observation,which will be helpful in recognizing the flow behavior of axisymmetriclaminar jet of low Reynolds numbers.     

AN EXPERIMENTAL AND NUMERICAL INVESTIGATION OF THE STARTING FLOW OF A UNIFORMLY ACCELERATING CIRCULAR CYLIINDER

The starting flow around a uniformly accelerated circular cylinder is investigatedby flow visualization techncque and solving N-S equations numerically in detail.The results ofthe starting flow are similar with those of the impulsively started one.At lower Re_α,numbers the“phenomenon a”is revealed;the“phenomenon β”appears at higher Re_α numbers,but withonly one secondary vortex.At the early stage of the starting vortex formation,the flow islaminar;at the later stage,the flow transforms into turbulent flow.The velocity distribution inthe flow field is measured with the multiwires installment.The calculational results are comparedwith the results of experiment,and both are in agreement with each other.     

NUMERICAL STUDY OF VORTEX SHEDDING FROM A SQUARE CYLINDER AND ITS EFFECTS ON HEAT TRANSFER OF MIXED CONVECTION

1 .　INTRODUCTIONForseveraldecades ,thenumericalandexperi mentalinvestigationofvortexsheddingfromaheated cooledbluntbodyinthemixednaturalandforcedconvectionregimeshasbeenasubjectofgreatinterestamongappliedmathematicians,fluiddynamicistsandheattransferanalysistowingtoitsnumerousengineeringapplicationssuchasthecoolingofelectroniccomponents ,thecoolingofhotwireanemometersandtheliftenhancementasattributedtotheMagnuseffects .Literatureonvortexsheddingfromcircularcylinderinthemixedconvectionregi…     

NUMERICAL SIMULATION OF DISCONTINUOUS FLOW IN CIRCULAR CONDUITS

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AN EXPERIMENTAL STUDY OF FLOW FIELD IN THE FLUID HOMOGENIZER

A Laser Doppler Anemometer (LDA) is used to measure and study the flow field in the working chamber of a homogenizer. Flow Patterns, distributions of mean and fluctuating velocities, shear rates are obtained in details. The characteristics of the flow field and the basic principles of homogenizing are presented. These results are very helpful for the improvement of fluid homogenizers.     

HYDRODYNAMIC FORCE ON SMOOTH HORIZONTAL CYLINDER IN UNIFORM OSCILLATORY FLOW

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MEASUREMENT OF HYDRODYNAMIC FORCES ACTING ON A CIRCULAR CYLINDER NEAR A PLANE BOUNDARY IN STEADY FLOW

In this paper,the characteristics of hydrodyna(?) forces on a circular cylindernear a plane boundary have been studied experimentally in w(?) tunnels.The drag coefficientC_D,mean lift coefficient C_(L0),T.m.s.lift coefficient C_(L Tms),maximum lift coefficient C_(L max) andfluctuating lift coefficients C'_(L Tms),C'_(L max),and lift(vortex shedding)frequency have been mea-sured on condition that the thickness of plane boundary layer,δ,was 0.1D(D is the diameter ofthe cylinder)at the station of the centre of the cylinder,and Reynolds number,Re,varied from4.5×10~3 to 1.76×10~5.The regularity of the change of these coefficients with Re and gap ratioG/D is found.The measurement of the lift frequency shows that a strong non-linear coupling ac-tion appears when the gap ratio between the circular cylinder and plane,G/D,reaches 0.5,andthe shedding of regular vortex is suppressed when G/D=0.2.     

NUMERICAL SIMULATION OF AN OSCILLATING FLOW PAST A CIRCULAR CYLINDER IN THE VICINITY OF A PLANE WALL

Oscillating flow around a circular cylinder in the vicinity of a plane wall was investigated by solving the two-dimensional incompressible Navier-Stokes equations with a finite element Galarkin residual method. The effect of the gap G/D between the cylinder surface and the wall on the flow behavior was studied. For the case of G/D 〈 0.25, the periodicity in the flow is attributed to both the outer shear layer instability and the oscillating frequency. As G/D 〉 0.25, vortex shedding occurs and the periodicity in the flow is mainly due to the competition of the oscillating frcqucncy and the vortex shedding frequency from an isolated stationary cylinder.     

STUDY OF VORTEX CHARACTERISTICS OF THE FLOW AROUND A HORIZONTAL CIRCULAR CYLINDER AT VARIOUS GAP-RATIOS IN THE CROSS-FLOW

1. INTRODUCTION The flow around a horizontal circular cylinder near a plane boundary (fixed wall) is of great significance in Hydrodynamics. For instance, sewagepipelines in water body of rivers in environmental engineering, conveying pipelines and optica…     

NUMERICAL SIMULATION OF THREE-DIMENSIONAL VORTEX DYNAMICS IN WAKE OF A CIRCULAR CYLINDER

The studies concerning the wake transition regime of the flow around a circular cylinder have drawn much attention in these years. Many experiments have been conducted for this problem but no accurate three-dimensional numerical simulations have hitherto been made. In this paper, a parallel procedure was developed to solve the three-dimensional Navier-Stokes equations on an SGI Origin3900 machine. Two different parallel strategies on this application were analyzed about their efficiency. It is found that the critical Reynolds number is 195, and the wake flow below this Reynolds number is purely two dimensional one, while the Reynolds number goes beyond this critical point, the wake flow becomes unstable under three-dimensional small disturbances. The transition regime involves two modes of small-scale three-dimensional instability (modes A and B), depending on the regime of Reynolds number ( Re ). It is also found that the two different modes A and B exhibit different physical features of the flow. And many other important questions were addressed in this paper.     

NUMERICAL STUDY OF FLOW AROUND AN OSCILLATING DIAMOND PRISM AND CIRCULAR CYLINDER AT LOW KEULEGAN-CARPENTER NUMBER

In order to identify the influence of shape corners on the instantaneous forces in the case of oscillating bodies, the simulated flow field is compared for two kinds of cross sections: diamond prism and circular cylinder. For these two flow configurations, the same Reynolds number and a Keulegan-Carpenter are considered. To compute the dynamic flow field surrounding the body, the Navier-Stokes transport equations in a non-inertial reference frame attached to the body are considered. Hence, a source term is added locally to the momentum equation to take into account the body acceleration. The proposed model is solved using the PHOENICS code. For the oscillating circular cylinder, the simulated results are in good agreement with the experimental data available in the litterature. After validation of this proposed model, flow field for diamond prism is determined. For both bodies, the process of the vortex formation is similar, with the formation of a recirculation zone in the near-wake containing a symmetric pair of vortices of equal strength and opposite rotation. The length of recirculation zone varies approximately linearly with time. However, the in-line force coefficient of the oscillating diamond prism is found to be greatest, since the recirculation zone is longer compared with that of the oscillating circular cylinder.     

NUMERICAL STUDY OF PARTICLE DISTRIBUTION IN THE WAKE OF GAS-PARTICLE TWO-PHASE FLOWS PAST A CIRCULAR CYLINDER AT HIGH REYNOLDS NUMBER

1. INTRODUCTION Particle ladengasflowspastcircularcylinders areoftenencounteredinindustrial,environmental andenergy relatedprocesses.Becausethegas flowspastcircularcylindersarecharacterizedby thedevelopmentofwakevortices,itwouldsuffice tosaythatunderstandingthemechanismofparti cledistributioninthewakeofcircularcylindersis crucialforreliablepredictions.Thenumericalstudiesofparticledispersioninplanemixinglay ers,planjets,andsprayshavebeenmadeexten sively,anditwasfoundthatthelargeorganized…     

A NEW WAKE OSCILLATOR MODEL FOR PREDICTING VORTEX INDUCED VIBRATION OF A CIRCULAR CYLINDER

This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current. The near wake dynamics related with the fluctuating nature of vortex shedding is modeled based on the classical van der Pol equation, combined with the equation for the oscillatory motion of the body. An appropriate approach is developed to estimate the empirical parameters in the wake oscillator model. The present predicted results are compared to the experimental data and previous wake oscillator model results. Good agreement with experimental results is found.     

STRUCTURES OF CONFINED VORTEX BREAKDOWN IN CONSTANT DIAMETER PIPE FLOW

Numerical solutions of three-dimensional, incompressible and unsteady Navier-Stokes equations for constant diameter swirling pipe flows are used to study vortex breakdown, including the detailed flow structures in the bubble domain and the “tail” behind the bubble during the vortex breakdown, and a comparison is made between the numerical solutions and the experimental results.     

PROPULSIVE PERFORMANCE AND VORTEX SHEDDING OF A FOIL IN FLAPPING MOTION

1 .　INTRODUCTIONInsectsandfishhaveexperiencedabillions yearprocessofevolutionwithnaturalselectionfortheirsurvivalandhavedevelopedtheirsuperiorandcomplete performanceofflightandswim ming .Usually ,aflappingmotionisabasicmodeoflocomotionforinsects ,birds ,andfish .Thrustandliftaregeneratedwhentheflappingwingsortailsinteractwiththesurroundingfluids .Becauseofthehighlyunsteadynatureofviscousflowaroundaflappingwing ,itisfarfromsatisfactorytounderstandthephysicalmechanismandvortexsheddinginuns…