LARGE-EDDY SIMULATION OF THREE-DIMENSIONAL VORTICAL STRUCTURES FOR AN IMPINGING TRANSVERSE JET IN THE NEAR REGION

The three-dimensional vortical structures for an impinging transverse jet in the near region were numerically investigated by means of Large-Eddy Simulation (LES). The LES results reproduced the skewed jet shear layer vortices close to the jet nozzle and the scarf vortex in the near-wall zone, in good agreement with the experimental observations. Different vortical modes in the skewed jet shear layer close to the jet nozzle were identified depending upon the velocity ratio between jet and crossflow, namely changing from an approximately axisymmetric mode to a helical one with the velocity ratios varying from 20 to 8. Moreover, the scarf vortex wrapped around the impinging jet in the near-wall zone showed distinct asymmetry with regard to its bilateral spiral legs within the near region. And the entrainment of the ambient crossflow fluids by the scarf vortex in the near-wall zone was appreciably influenced by its asymmetry and in a large part occurred on the surface of the spiral roller structures in the course of spreading downstream.     

THEORETICAL AND EXPERIMENTAL INVESTIGATIONS OF ENTRAINED AND TRANSPORTED CHARACTERISTICS OF SUBMERGED JET

This paper presents entrainment mechanism, and transported and diffusion characteristics at the point of entry of submerged jet. The profiles of both velocity and concentration within the air water mixing layer were theoretically deduced. And the comparisons between theoretical values and measured data were made. Results show that the velocity profile within the air water mixing layer exhibits a form of error function. The concentrations of air entrainment in the internal and external regions of ai~water mixing layer correspond to Gaussian distribution.     

PDA MEASUREMENTS OF TWO-PHASE FLOW STRUCTURE AND PARTICLE DISPERSION FOR A PARTICLE-LADEN JET IN CROSSFLOW

The two-phase flow structure and particle dispersion for a dilute particle-laden jet in crossflow(JICF) were experimentally investigated by means of Phase Doppler Anemometry(PDA) measurement.The two-phase flow experiments were conducted for different flow conditions and solid particle parameters,including the ratio of the jet velocity to crossflow velocity,the particle size and mass loading.The experimental results indicate that the fine particles with the size of 70 micron and the mass loading of 0.05% hav...     

FLOW CHARACTERISTICS OF TURBULENT JETS INJECTED OBLIQUELY IN CROSSFLOW

1 .　INTRODUCTIONThejetinacrossflowisahighlycomplexturbu lentflow ,andwithapplicationsinvariousengineeringfields .Theinjectionofajetintothecrossflowcanaltertheflowfieldandresultinaverycomplexthree di mensionalflowstructure .Numericalsimulationisanimportantmethodtostudythetransversejet cross flow .Chang[1] ,Tamamidis[2 ] ,Lakehal[3] etc .,usedthenormalk εmodelandwallfunctionmethodtosim ulatetheflowfieldoftheturbulentjet .Althoughthenormalk εmodelgivespredictionsofengineeringaccu racyint…     

NUMERICAL SIMULATION OF LAMINAR SQUARE IMPINGING JET FLOWS

A theoretical study has been undertaken to determine the flow characteristics associated with a three-dimensional laminar impinging jet issuing from a square pipe nozzle. Interesting flow structures around the jet are detected. The numerical result reveals the existence of four streamwise velocity off-center peaks near the impingement plate, which is different from the rectangular jet impingement. The mechanism of the formation of the off-center velocity peaks and the parameters affecting the flow-field characteristics are discussed by comparison of the computed results with different nozzle-to-plate spacings and Reynolds numbers.     

NUMERICAL STUDY OF TURBULENT IMPINGING JET WITH A REFINED k-ε MODEL

1.　INTRODUCTIONJet impingement flows are frequently used in industrial practice for their high rate ofheat and mass transfer.Their employment is common but also diverse and typical applica-tions includemany heating,cooling and drying processessuch asthe manufacturing of print-ed wiring board,printing processes,production of foodstuffs,de-icing of aircraft wings,cooling of electronic elements and package and cooling of turbine aerofoils.The high heattransfer rate are especially needed to a…     

COMPUTATIONS FOR PLANE TURBULENT IMPINGING JET IN CROSS FLOW

ＮＯＭＥＮＣＬＡＴＵＲＥａ1ａｎｄａ2　　　　ｃｏｎｓｔａｎｔｓｉｎ(14)ｂｈａｌｆｗｉｄｔｈｗｈｅｒｅｕ=ｕｍ2ｃ1,ｃ2ａｎｄｃμｃｏｎｓｔａｎｔｓｏｆｋεｍｏｄｅｌｓｆ1ａｎｄｆ2ｆｕｎｃｔｉｏｎｓｍａｒｋｉｎ(13)Ｈｔｈｅｄｅｐｔｈｏｆｔｈｅｆｌｕｍｅｆ?..     

SCALE EFFECT OF IMPINGING PRESSURE CAUSED BY SUBMERGED JET

The characteristics of the impinging pressure at the jet equipment where the maximum jet velocity can reach 50m/s were studied. By comparing the impinging pressure with the one measured at the low velocity conditions, two conclusions of the scale effect are drawn： firstly, the velocity attenuation degree is smaller than that of low velocity jet, and secondly, the relative impinging width is narrower than that of low-velocity jet. The reasons of the scale effect of the impinging pressure were elucidated through numerical simulation.     

APPLICATION OF TWO VERSIONS OF A RNG BASED k-ε MODEL TO NUMERICAL SIMULATIONS OF TURBULENT IMPINGING JET FLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＤｕｒｉｎｇｔｈｅｐａｓｔｔｈｒｅｅｄｅｃａｄｅｓ,ｔｈｅｋ εｍｏｄｅｌｈａｓｐｌａｙｅｄａｃｅｎｔｒａｌｒｏｌｅｉｎｔｈｅｃａｌｃｕｌａｔｉｏｎｏｆｍａｎｙｏｆｔｈｅｔｕｒｂｕｌｅｎｔｆｌｏｗｓｏｆｓｃｉｅｎｔｉｆｉｃａｎｄｅｎｇｉｎｅｅｒｉｎｇｉｎｔｅｒｅｓｔ.Ｉｎｔｈｉｓｔｗｏ ｅｑｕａｔｉｏｎｍｏｄｅｌ,ｔｈｅｔｕｒｂｕｌｅｎｃｅｌｅｎｇｔｈａｎｄｔｉｍｅｓｃａｌｅｓａｒｅｂｕｉｌｔｕｐｆｒｏｍｔｈｅｔｕｒｂｕｌｅｎｔｋｉｎｅｔｉｃｅｎｅｒｇｙｋａｎｄｄｉｓｓｉ…     

EXPERIMENTAL STUDY ON THE VORTEX FORMATION AND ENTRAINMENT CHARACTERISTICS FOR A ROUND TRANSVERSE JET IN SHALLOW WATER

The vortex formation and entrainment characteristics for a round transverse jet in shallow water were experimentally investigated by means of a combination of LIF flow visualization and PIV measurement. A scarf vortex wrapped around the main body of the jet is formed in the near-wall region due to the interaction between the resulting wall jet and sufficiently shallow crossflow, with some more or less unsteady flow properties and with spreading ranges as functions of both the velocity ratio and the water depth within the near field. The entrainment of the ambient crossflow fluid into the jet main body is closely associated with the time-evolving features of the shear layer between the jet and surrounding fluid as well as the induced vortical structures near the wall. In the case of slight impingement upon the wall, the interaction between the jet shear layer and the weak, unstable scarf vortex gives rise to an appreciable local entrainment enhancement, confined in the near-wall region in the vicinity of the stagnation point. While in the case of intense impingement upon the wall, the well-organized and stable scarf vortex gives rise to a greatly enhanced entrainment and a greatly increased lateral spreading rate nearly throughout the overall near field as compared to the conventional wall jet. In addition, the entrainment of the ambient crossflow fluid by the scarf vortex in this case occurs largely on the surface of the unique spiral roller structure by itself due to the presence of smaller and unorganized eddies, and accordingly the scarf vortex is likely to keep its spiral roller structure steadily to a relatively great downstream distance within the near field.     

DILUTION OF HORIZONTAL RADIAL JET IN A CURRENT

A type of port with a movable cover is designed to increase initial dilution andprevent sea water and sediments from intruding into outfall systems.Horizontal radial jets pro-duced by this type of port in a current are investigated experimentally and theoretically.Theanalysis based on Reynolds'equations and self-similarity hypothesis shows that the maximum ve-locity of radial jets decays with r~(-1.5).The relationships between the width,thickness,average di-lution of a submerged wastefield along flow,and the parameters of the port,jet and ambient areestablished quantitatively and verified by experiments.It is demonstrated that the dilution ofhorizontal radial jets is much higher than that of vertical round jets and the surface boil point ofthe former is much more distant than that of the latter.     

NUMERICAL SIMULATION OF THE FORMATION OF NANOPARTICLES IN AN IMPINGING TWIN-JET

The Large Eddy Simulation (LES) method has been used to solve the fluid momentum equations coupled with a convection-diffusion equation to study the formation of pollutant nanoparticles in a vehicular exhaust with impinging twin-jet. The functions of the space (S) between the two jets and the distance (H) from the exit of nozzle to the impingement plane are evaluated according to the distributions of pollutant nanoparticles. The results show that the nucleation produces a large number of nanoparticles, and gas-to-nanoparticle conversion mostly takes place in the interface region of the two jets, the circumambience of the jets, and region near the plane. The maximal particle size and maximal number concentration produced by both nucleation and coagulation appear around the region of free jet and the region near the plane, respectively. The significant differences for various spaces between the two jets are the number concentration and size distributions in the interface region of the two jets. For the case with larger space, more nanoparticles are produced by nucleation and coagulation. The more the distance from the exit of nozzle to the impingement plane, the lower is the number concentration and the fewer the particles distribute near the plane. Increasing the distance from nozzle to plane is beneficial to the reduction of nanoparticle formation.     

ON THE SELF-SIMILARITY OF A JET IN CROSSFLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｊｅｔｉｎｃｒｏｓｓｆｌｏｗ ,ｗｉｔｈｈｉｇｈｌｙｃｏｍｐｌｉｃａｔｅｄｔｕｒｂｕｌｅｎｃｅ ,ｉｓａｃｌａｓｓｉｃｆｌｏｗ ｐｒｏｂｌｅｍｉｎｆｌｕｉｄｍｅｃｈａｎｉｃｓ.Ｓｉｍｕｌｔａｎｅｏｕｓｌｙ ,ｉｔｉｓｃｒｕｃｉａｌｔｏｍａｎｙｅｎｇｉｎｅｅｒｉｎｇａｐｐｌｉｃａｔｉｏｎｓ .Ｅｘａｍｐｌｅｓｉｎｅｎｖｉｒｏｎｍｅｎｔａｌｓｉｔｕａｔｉｏｎｓａｒｅｄｉｓｃｈａｒｇｅｏｆｓｔａｃｋｅｍｉｓｓｉｏｎｉｎｔｏｔｈｅａｔｍｏｓｐｈｅｒｅａｎｄｏｆｗａｓｔｅｗａｔｅ…     

AN EXPERIMENTAL STUDY ON THREE DIMENSIONAL STRUCTURE OF BAROCLINIC WAVY JET STREAM IN A ROTATING ANNULUS SUBJECT TO RADIAL TEMPERATURE GRADIENT

1.　INTRODUCTIONThe research on jet,which is a typical flow pattern in atmosphere,has made a greatprogress in both theory and observation.There existsa striking similar feature between thejetstream of baroclinic fluid in a rotating annulussystem and the defined one of IMO( Inter-national Meteorological Organization,Upper Air Technical Commission) .Forsuch a similarfeature,more and more attention hasfocused on the experimental simulation of jetstream ina baroclinic fluid system based on…     

EXPERIMENTAL STUDY ON THE EFFECTS OF AIR ENTRAINMENT ON A PLANE JET DIFFUSION IN A PLUNGE POOL

l'mTRODUrmNThisworkwasmotivatedbythepotentialapplicationOftheerosionofplungepoolsdownstreamofdamscausedbysubmergedwaterjets.TheerosionorscourofplungepoolsoccursatthePointofajetimpact.Thescourprocesshasbeeninvestigatedformanyyears.Thescourdepthestimatedfromformulasdevelopedoveryears,however,indicatesawidevariation(MasonandArumugam,l985)-Mostoftheseformulasinvolveanexpressioninwhichscourdepthisafunctionofthedischargeperunitwidth,theheaddropandthechar-acteristicsizeofthebedmaterial.Arecentin…     

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.     

EXPERIMENTAL INVESTIGATIONS ON DIFFUSION CHARACTERISTICS OF HIGH CONCENTRATION JET FLOW IN NEAR REGION

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｒｅｓｅａｒｃｈｏｆｊｅｔｉｓａｎｉｍｐｏｒｔａｎｔｆｉｅｌｄｉｎｆｌｕｉｄｍｅｃｈａｎｉｃｓ.Ｉｔａｌｓｏｈａｓｍａｎｙａｐｐｌｉｃａｔｉｏｎｓｉｎｅｎｇｉｎｅｅｒｉｎｇ ,ｆｏｒｅｘａｍｐｌｅ ,ｔｈｅｄｉｓｃｈａｒｇｅｏｆｐｏｌｌｕｔａｎｔａｎｄｃｏｏｌｉｎｇｗａｔｅｒｉｎｉｎｄｕｓｔｒｉｅｓ .Ｗｈｅｎｔｈｅｉｎｉｔｉａｌｄｅｎｓｉｔｙｏｆｔｈｅｊｅｔｉｓｄｉｆｆｅｒｅｎｔｆｒｏｍｔｈａｔｏｆｔｈｅａｍｂｉｅｎｔｗａｔｅｒｂｏｄｙ ,ｔｈｅｊｅｔｗｉｌｌｂｅａｆ…     

CHARACTERISTICS OF CORRELATION AND SPECTRUM BETWEEN WALL FLUCTUATING PRESSURE AND FLUCTUATING VELOCITY OF IMPINGING JET

The correlation, the spectrum and the turbu-lent scale between wall fluctuating pressure and fluctuating ve-locity, on the bed of plunging pool under the action of single and twin impinging jet, are investigated in the paper by using 2-D LDA and the dynamic pressure scanning system of multi-ple points. It is found that the cross correlation between the horizontal fluctuating velocity and the fluctuating pressure of twin jet is bigger than that of sinlge jet, and the spectrum be-tween horizontal fluctuating velocity and fluctuating pressure obviously has approximately dominant frequency. The rela-tionship between the fluctuation pressure coefficient on wall and the turbulent intensity near the wall can be described with logarithmic curve.     

THE CHARACTERISTICS OF TURBULENCE AND DISPERSION IN SURFACE LAYER OF COASTAL REGION

By analyzing turbulence data measured at two sites in coastal regions of Hangzhoubay,it is discovered that:(1)The turbulent intensity I_k is inversely proportional to the windspeed at lower speed.While at higher wind speed,it keeps basically to be constant.(2)Underthe unstable conditions in the vicinity of sea shore,the dimensionless standard deviations of windspeed σ_k/U(?) are constants basically,while in the inland,they can be described by the expressionssimilar to Panofsky(1977)models but with different constants.Under the stable conditions,they are constants when Z/L<0.2 and proportional to 1/3 power of Z/L for larger Z/L.(3)Near the coast,the variation of U(?)/U with Z/L follows Businger(1971)model U(?)/U =k/(?)(Z/L)very well not only under stable but also under unstable condition.Inland,it is coincidentvery well merely under the condition-1.0≤Z/L≤0.3.Out this range,the deviation islarge.(4)The dispersion parameters can be described in the form recommended by Draxler(1976)but with different constants.Under the unstable condition,they can also be expressed asBriggs(1985)model with different constants.     

NUMERICAL SIMULATION OF A HORIZONTAL MOMENTUM JET IN CROSS-FLOW

1. INTRODUCTIONWhen a momentumjet is issuing vertically orhorizontally into a steady ambient cross-flow, amomentumjet in cross-flowis formed as shown inFig .1 .The phenomena canfrequently foundin na-ture ,as well as inindustrial projects .Examples in-clud…