CFD numerical simulation of flow velocity characteristics of hydrocyclone

A CFD based numerical simulation of flow velocity of hydrocyclone was conducted with different structural and operational parameters to investigate its distribution characteristics and influencing mechanism. The results show there exist several unsymmetrical envelopes of equal vertical velocities in both upward inner flows and downward outer flows in the hydrocyclone, and the cone angle and apex diameter have remarkable influence on the vertical location of the cone bottom of the envelope of zero vertical velocity. It is also found that the tangential velocity isolines exist in the horizontal planes located in the effective separation region of hydrocyclone. The increase of feed pressure has almost no effect on the distribution characteristics of both vertical velocity and tangential velocity in hydrocyclone, but the magnitude and gradient of tangential velocity are increased obviously to make the motion velocity of high density particles to the wall increased and to make the cyclonic separation effect improved.

Idealized Numerical Simulations of Tropical Cyclone Formation Associated with Monsoon Gyres

Monsoon gyres have been identified as one of the important large-scale circulation patterns associated with tropical cyclone （TC） formation in the western North Pacific.A recent observational analysis indicated that most TCs form near the center of monsoon gyres or at the northeast end of the enhanced low-level southwesterly flows on the southeast-east periphery of monsoon gyres.In the present reported study,idealized numerical experiments were conducted to examine the tropical cyclogenesis associated with Rossby wave energy dispersion with an initial idealized monsoon gyre.The numerical simulations showed that the development of the low-level enhanced southwesterly flows on the southeasteast periphery of monsoon gyres can be induced by Rossby wave energy dispersion.Mesoscale convective systems emerged from the northeast end of the enhanced southwesterly flows with mid-level maximum relative vorticity.The simulated TC formed in the northeast of the monsoon gyre and moved westward towards the center of the monsoon gyre.The numerical experiment with a relatively smaller sized initial monsoon gyre showed the TC forming near the center of the initial monsoon gyre.The results of the present study suggest that Rossby wave energy dispersion can play an important role in TC formation in the presence of monsoon gyres.

STATISTICAL ANALYSIS AND NUMERICAL SIMULATION OF POYANG LAKE'S INFLUENCE ON TROPICAL CYCLONES

Based on the Tropical Cyclone(TC briefly thereafter)Yearbook 1980-2009,this paper first analyzes the number and intensity change of the TCs which passed directly over or by the side of Poyang Lake(the distance of TC center is less than 1°longitude or 1°latitude from the Lake)among all the landfalling TCs in China during the past 30 years.Two cases are examined in detail in this paper.One is severe typhoon Rananim with a speed of 3.26 m/s and a change of 1 hPa in intensity when it was passing the Lake.The other is super typhoon Saomai with a faster moving speed of 6.50 m/s and a larger change in intensity of 6 hPa.Through numerical simulation experiments,this paper analyzes how the change of underlying surface from water to land contributes to the differences in intensity,speed and mesoscale convection of the two TCs when they passed the Lake.Results show that the moisture and dynamic condition above the Lake were favorable for the maintenance of the intensity when Rananim was passing through Poyang Lake,despite the moisture supply from the ocean was cut off.As a result,there was strong convection around the lake which led to a rainfall spinning counter-clockwise as it was affected by the TC movement.However,little impact was seen in the Saomai case.These results indicate that for the TCs coming ashore on Poyang Lake with a slow speed,the large water body is conducive to the sustaining of the intensity and strengthening of the convection around the TC center and the subsequent heavy rainfall.On the contrary,a fast-moving TC is less likely to be influenced by the underlying surface in terms of intensity and speed.

A METHOD OF INITIAL VORTEX RELOCATION AND NUMERICAL SIMULATION EXPERIMENTS ON TROPICAL CYCLONE TRACK

Using the technique of smooth filtering and cylindrical filtering,the initial vortex circulation and large-scale environmental field were separated from the background field.Then the separated initial vortex circulation was translated and reinserted in the location where it was observed.This led to the determination of a method of initial vortex relocation.For seven tropical cyclones at 23 points of measurement time in the years of 2006 and 2007,two schemes,either directly adding a tropical cyclone bogus model in the background or adding it after the relocation of the initial vortex in the background field,were employed.Simulation experiments were compared.The results showed that the mean errors of the simulated tropical cyclone tracks at 24 and 48 hours were both smaller with the scheme of adding tropical cyclone bogus model after the relocation of the initial vortex in the background field.The relocation method of the initial vortex decreases the error caused by the deviation of the initial tropical cyclone location in tropical cyclone models.The relocation method is conducive to improving the track forecast of tropical cyclone models and has a good perspective for operational application.

STATISTICAL ANALYSIS OF SUMMER TROPICAL CYCLONE REMOTE PRECIPITATION EVENTS IN EAST ASIA FROM 2000 TO 2009 AND NUMERICAL SIMULATION

Using 1°×1° final analysis(FNL) data from the National Centers for Environmental Prediction(NCEP),precipitation data from the Tropical Rainfall Measuring Mission(TRMM) and the best-track tropical cyclone(TC)dataset provided by the Japan Meteorological Agency(JMA) for June-August of 2000-2009, we comprehensively consider the two factors low-level moisture channel and interaction between TCs and mid-latitude systems and implement a statistical analysis of remote precipitation in East Asia to the north of 0° and to the west of 150° E. 48 cases of remote precipitation occurred in this period, which are categorized into five classes. After a composite analysis of the different classes, the main systems at 850 h Pa and 500 h Pa that impact the remote precipitation are as follows:TC, mid-latitude trough, subtropical high and water vapor channel. In particular, the water vapor channel which usually connects with Indian monsoon has the most significant impact on remote heavy rainfall. Another important factor is the mid-latitude trough. The type of north trough/vortex-south TC remote precipitation events happen most frequently,accounting for 68.8% of the total incidence. Most remote precipitation events occur on the right side of the TC path(representing 71% of the total number). At 200 h Pa, the remote precipitation events usually occur on the right rear portion of a high-altitude jet stream, and there is an anti-cyclonic vortex to the east and west of the TCs. When there is no anti-cyclonic vortex to the east of the TC, the TC is relatively weak. When the remote precipitation occurs to the northwest of the TC and there is a trough in the northwest direction, the TC is relatively strong. Numerical experiments are carried out using Weather Research and Forecast(WRF) model. The results shows that the TC plays a main role in producing the heavy precipitation and results in the enhancement of precipitation by impacting the water vapor channel.

Experimental study and numerical simulation of gas-particle flows with radial bias combustion and centrally fuel rich swirl burners

Numerical simulation is applied to gas-particle flows of the primary and the secondary air ducts and burner region, and of two kinds of swirl burners. The modeling results of Radial Bias Combustion (RBC) burner well agreed with the data from the three-dimensional Phase-Doppler anemometry (PDA) experiment by Li, et al. The modeling test conducted in a 1025 t/h boiler was to study the quality of aerodynamics for a Central Fuel Rich (CFR) burner, and the Internal Recirculation Zone (IRZ) was measured. In addition, gas-particle flows with a CFR burner were investigated by numerical simulation, whose results accorded with the test data fundamentally. By analyzing the distribution of gas velocity and trajectories of particles respectively, it is found that the primary air’s rigidity of CFR burner is stronger than that of RBC burner, and the primary air mixes with the secondary air later. Furthermore, high concentration region of pulverized coal exists in the burner’s central zone whose atmosphere is reduced, and trajectories of particles in IRZ of CFR burner are longer than that of RBC burner. They are favorable to coal’s ignition and the reduction of NOx emission.

Effect of Sea Spray on the Numerical Simulation of Super Typhoon ‘Ewiniar’

To study the potential effect of sea spray on the evolution of typhoons,two kinds of sea spray flux parameterization schemes developed by Andreas (2005) and Andreas and Wang (2006) and Fairall et al. (1994) respectively are incorporated into the regional atmospheric Mesoscale Model version 3.6 (MM5V3) of Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) and the coupled atmosphere-sea spray modeling system is applied to simulate a Western Pacific super ty-phoon Ewiniar in 2006. The simulation results demonstrate that sea spray can lead to a significant increase in heat fluxes at the air-sea interface and the simulated typhoon’s intensity. Compared with the results without sea spray,the minimum sea level pressure reduces about 8hPa after taking account of sea spray by Fairall et al.’s parameterization (1994) and about 5hPa by Andreas’ (2005) and Andreas and Wang’s (2006) parameterization at the end of the model integration,while the maximum 10m wind speed increases about 17% and 15% on average,respectively,through the entire simulation time period. Taking sea spray into account also causes significant changes in Tropical Cyclone (TC) structure due to an enhancement of water vapor and heat transferred from the sea sur-face to the air; therefore,the center structure of the typhoon becomes more clearly defined and the wind speed around the typhoon eye is stronger in numerical experiments. The simulations show that different sea spray flux parameterizations make different modi-fications to the TC structure.

Numerical Simulation of Dust Removal in the Cyclone Collector of a Straw Crusher Based on a Discrete Phase Model

The cyclone dust collector is an important subsystem of straw crushers used in agriculture.In the present study,a new type of dust collector with involute morphology is proposed to obtain better dust removal efficiency with respect to that of classical tangential and spiral dust collectors.A discrete phase model(DPM)method is used in synergy with a turbulence model,and the SIMPLE algorithm to simulate the flow field inside the dust collector and the related particle dynamics.It is shown that the internal flow field features a primary swirl,a secondary swirl and blockage effects.Moreover,for the involute dust collector,the tangential velocity in the initial stage and the pressure in the high-pressure area are larger than those obtained for the classical types.The dust removal efficiency is 37.11%,25.3%,and 16.37%for the involute type dust collector,the tangential type and the spiral type,respectively.

Numerical simulation of the flow field in a dense-media cyclone

An analytical study of the flow and pressure fields inside a small-diameter dense-media cyclone is presented.The simulations were done with the help of the CFD software FLUENT.The following conclusions were reached:the tangential velocity tends to increase when moving from the center toward the exterior.The velocity then begins to decrease when the maximum velocity point is reached.The velocity field divides into two different sections;an inner swirling zone and an outer swirling zone.The axial velocity points down at the wall and gradually decreases toward the bottom.Continuing toward the bottom,the axial velocity passes through zero and then gradually increases in the opposite direction.In the cyclone's central zone,the pressure is negative and the suction of air allows an air column to be formed therein.At the center of the radial negative zone the pressure drops to its lowest value—phenomenon that has been verified by theoretical analysis.Some discrepancies between the observed data and the simulated data are noted when an analysis in made on a cyclone operating with either fresh water only or with water with added heavy particles.

A Dynamic Analysis and Numerical Simulation of Explosive Development of an Extratropical Cyclone Over Land

The present paper has made a dynamic and diagnostic study of the process of explosive deepening of an extratropical cyclone over North China on April 25-26, 1983, in order to gain an insight into the physical mechanism of explosive development of cyclone over land. It turns out that this cyclone occurred in the strong baroclinic zone, and the vorticity and thermal advection triggered the initial development of the cyclone. Subsequently, as the rainfall increased, the effect of condensational heating became more and more important. During the time period of rapid intensification (from 1200GMT 25 to 0000GMT 26 April, 1983, the central surface pressure fell down from 998. 2 to 988. 3 hPa), the peak of diabatic heating profile continuously descended, leading to a rapid increase in heating amount in the lower troposphere. This condition is favorable to the explosive development of rotational circulation or vortex. The numerical simulations have further demonstrated the importance of the lowering of heating peak for the rapid development of the cyclone.

NUMERICAL SIMULATION OF THREE DIMENSIONAL GAS-PARTICLE FLOW IN A SPIRAL CYCLONE

The three-dimension gas-particle flow in a spiral cyclone is simulated nu- merically in this paper. The gas flow field was obtained by solving the three-dimension Navier-Stokes equations with Reynolds Stress Model （RSM）. It is shown that there are two regions in the cyclone, the steadily tangential flow in the spiral channel and the combined vortex flow in the centre. Numerical results for particles trajectories show that the initial position of the particle at the inlet plane substantially affects its trajectory in the cyclone. The particle collection efficiency curves at different inlet velocities were obtained and the effects of inlet flow rate On the performance of the spiral cyclone were presented. Numerical results also show that the increase of flow rate leads to the increase of particles collection efficiency, but the pressure drop increases sharply.

THREE-DIMENSIONAL NUMERICAL SIMULATION OF TROPICAL CYCLONE AND THE EFFECTS OF RADIATIVE PROCESSES ON IT

In this paper, a three-dimensional primitive equation numerical model includingvarious physical processes is constructed. Using this model, the development and thestructure of the tropical cyclone (typhoon) are first successfully simulated. Then theeffects of radiative processes on the development of the cyclone are investigated. Theradiative processes and their parameterization include long wave, short wave radiationand cloud type and cloudiness respectively. The results show that the tropical cyclonewill develop earlier and more quickly after the effect of radiative processes isincorporated, but the differences in intensity between the two cases with and withoutradiative processes at the final state are not evident. Only at the developing stage hasthe cyclone affected by radiation a sharper decrease in the surface pressure, a strongerwind and upward motion. a more obvious eye and eyewall, etc. All the results showthat the radiative processes are important in the earlier development stage of thetropical cyclone.

Numerical Simulation on the Flow Field of a Four-channel Coal Burner

In this paper, the numerical simulation on the flow field of a four-channel coal burner was investigated with Fluent software. The three-dimension model was created with UG software. The structure was meshed by using Gambit software. The realizable K-ε turbulence model and simple method were adopted. The variation of the inner flow field of the burner was studied and analyzed. The results simulated to the burner by the realizable K-ε turbulence model show that the contours of theflowfield accord with the actual condition and the realizable K-ε model is proved to be feasible and the results of simulation are creditable. That will have important significance to the improvement of the structure and parameter optimization of the four-channel coal burner in the future.

NUMERICAL SIMULATIONS OF β-GYRES IN TROPICAL CYCLONES

The circulation of β-gyres in tropical cyclones is studied using numerical simulations. As shown in the result, there is clear circulation of β-gyres in the deviation flow field of the middle layer of the model,i.e. there is cyclone current west of the vortex center but anticyclone current east of it. The theory analysis shows that the circulation of β-gyres is formed by the advection of geostrophic vorticity.

Structural Changes of a Tropical Cyclone during Landfall: β-plane Simulations

This study investigated the effects of landfall on the structure of a tropical cyclone （TC）. Numerical simulations were performed using the Weather Research and Forecasting Model on a β-plane. Two landfall experiments, one with an east–west and another with a north–south oriented coastline, were performed. Similar to previous studies on an f-plane, large-scale flows in the low-to-middle troposphere were modified due to friction. A pair of counter rotating gyres was found, which was shown to be consistent with the slight deffection of the TC relative to the control experiment without land. Compared to previous f-plane simulations, because of the inherent asymmetries due to the β-gyres, the large-scale pattern of flows and convergences/divergences related to friction were found to depend on coastline orientations. On the other hand, regardless of the coastline orientation, convergences were found to be stronger to the left for both cases near landfall, as in previous f-plane simulations. Such a convergence pattern subsequently induced a change in convection and rainfall at the eyewall.

Impacts of Soil Moisture on the Numerical Simulation of a Post-Landfall Storm

Surface heat and moisture fluxes are important to the evolution of a tropical storm after its landfall. Soil moisture is one of the essential components that influence surface heating and moisture fluxes. In this study, the impact of soil moisture on a pre-landfall numerical simulation of Tropical Storm Bill(2015), which had a much longer lifespan over land, is investigated by using the research version of the NCEP Hurricane Weather Research and Forecasting(HWRF) model. It is found that increased soil moisture with SLAB scheme before storm's landfall tends to produce a weaker storm after landfall and has negative impacts on storm track simulation. Further diagnoses with different land surface schemes and sensitivity experiments indicate that the increase in soil moisture inside the storm corresponds to a strengthened vertical mixing within the storm boundary layer, which is conducive to the decay of storm and has negative impacts on storm evolution. In addition, surface diabatic heating effects over the storm environment are also found to be an important positive contribution to the storm evolution over land, but their impacts are not so substantial as boundary layer vertical mixing inside the storm. The overall results highlight the importance and uncertainty of soil moisture in numerical model simulations of landfalling hurricanes and their further evolution over land.

Numerical analysis on the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model

This study aims to analyze the influence of vortex motion in a reverse Stairmand cyclone separator by using LES model.The mathematical analysis indicated that the energy dissipation and the flow characteristics of incompressible fluid are directly related to on the vortex motion.The results of the Q criterion-based iso-vortex surface could well reflect the tendency of the vortex structure,in which the iso-vortex surface exhibited a distorted distribution rather than around the center axis.At the turning point of velocity vector,vortices were formed and developed,and the point was the center of the local vortex core.In addition,the vortex formed an irregular annular region around the wall at the bottom of vortex finder.The vortex structure near the dust hopper presented a strong distortion.Moreover,there were two rotating flow in the opposite direction within the dust hopper.These phenomena would affect the separation performance,which was significance to cyclone separator.

Numerical Simulation of the Genesis of Typhoon Durian (2001) over the South China Sea:the Effect of Sea Surface Temperature

Typhoon Durian (2001),which formed over the South China Sea (SCS),was simulated by using the Weather Research and Forecasting (WRF) model. The genesis of typhoon Durian which formed in the monsoon trough was reproduced by numerical simulations. The simulated results agree reasonably well with observations. Two numerical experiments in which the sea surface temperature (SST) was either decreased or increased were performed to investigate the impact of the SST on the genesis of the ty-phoon. When the SST was decreased by 5℃ uniformly for all grids in the model,the winds calculated became divergent in the lower troposphere and convergent in the upper troposphere,creating conditions in which the amount of total latent heat release (TLHR) was low and the tropical cyclone (TC) could not be formed. This simulation shows the importance of the convergence in the lower tropo-sphere and the divergence in the upper troposphere for the genesis of the initial vortex. When the SST was increased by 1℃ uni-formly for all grids,a stronger typhoon was generated in the results with an increase of about 10 m s-1 in the maximum surface wind speed. Only minor differences in intensity were noted during the first 54 h in the simulation with the warmer SST,but apparent dif-ferences in intensity occurred after 54 h when the vortex began to strengthen to typhoon strength. This experiment shows that warmer SST will speed the strengthening from tropical storm strength to typhoon strength and increase the maximum intensity reached,while only minor impact can be seen during the earlier stage of genesis before the TC reaches the tropical storm strength. The results sug-gest that the amount of TLHR may be the dominant factor in determining the formation and the intensification of the TC.

NUMERICAL SIMULATION ON RE-INTENSIFICATION OF TROPICAL REMNANT RE-ENTERING THE SEA:A CASE STUDY

When Typhoon Toraji(2001)reached the Bohai Gulf during 1-2 August 2001,a heavy rainfall event occurred over Shandong province in China along the gulf.The Advanced Research version of the Weather Research and Forecast(WRF-ARW)model was used to explore possible effects of environmental factors,including effects of moisture transportation,upper-level trough interaction with potential vorticity anomalies,tropical cyclone(TC)remnant circulation,and TC boundary-layer process on the re-intensification of Typhoon Toraji,which re-entered the Bohai Gulf after having made a landfall.The National Centers for Environmental Prediction(NCEP)global final(FNL)analysis provided both the initial and lateral boundary conditions for the WRF-ARW model.The model was initialized at 1200 UTC on 31 July and integrated until 1200 UTC on 3 August 2001,during which Toraji remnant experienced the extratropical transition and re-intensification.Five numerical experiments were performed in this study,including one control and four sensitivity experiments.In the control experiment,the simulated typhoon had a track and intensity change similar to those observed.The results from three sensitivity experiments showed that the moisture transfer by a southwesterly lower-level jet,a low vortex to the northeast of China,and the presence of Typhoon Toraji all played important roles in simulated heavy rainfall over Shandong and remnant re-intensification over the sea,which are consistent with the observation.One of the tests illustrated that the local boundary layer forcing played a secondary role in the TC intensity change over the sea.

A SIMULATION STUDY OF THE INFLUENCE OF LAND FRICTION ON LANDFALL TROPICAL CYCLONE TRACK AND INTENSITY

A quasi-geostrophic barotropic vorticity equation model is used to simulate the influences of topographic forcing and land friction on landfall tropical cyclone track and intensity. The simulation results show that tropical cyclone track may have sudden deflection when the action of topographic friction dissipation is considered, and sudden deflection of the track is easy to happen and sudden change of tropical cyclone intensity is not clear when the intensity of tropical cyclone is weak and the land friction is strong. The land friction may be an important factor that causes sudden deflection of tropical cyclone track around landfall.