Understanding the bubble behaviours and flow characteristics of large-capacity bottom-blowing electric arc furnace(EAF)is crucial for potential exogenous gas-induced slag foaming process and enhancement of molten bath...Understanding the bubble behaviours and flow characteristics of large-capacity bottom-blowing electric arc furnace(EAF)is crucial for potential exogenous gas-induced slag foaming process and enhancement of molten bath dynamics.A physical model and a 3D gas-slag-steel transient bottom-blowing numerical model of a 150 t EAF were established to investigate the bubble behaviour and flow characteristics throughout the molten steel bath and slag layer under bottom-blowing,with referring to gas flow rate,plug diameter,plug arrangement and injection angle.Results indicate that the average bubble sizes experience increase,dynamic stability and decrease in molten steel bath and then undergo decrease and increase after entering into slag layer for all bottom-blowing modes.The bubble numbers exhibit the opposing trends during the process.Increase in gas flow rate leads to a significant rise in average bubble size but a decrease in number,average dwelling time and the spread area of bubbles in slag layer.Increase in plug diameter causes an opposite impact.The effect of plug arrangement radii on bubbles is almost negligible.Increasing the injection angle results in an increase in bubble size and a decrease in both bubble number and dwelling time in slag layer.The slag foaming potential was discussed referring to the bubble size,number and dwelling time in slag layer.Increase in gas flow rate and plug diameters can significantly enhance the fluids flow through increasing average flow velocity,decreasing mixing time and dead zone ratio of molten bath.Plug arrangement radius and injection angle express nonlinear correlation with average flow velocity and dead zone ratio,and the plug arrangement radius of 0.5R(R represents the radius of bottom circle of EAF model)and injection angle of 15°perform better in enhancing dynamics of molten bath.A group of bottom-blowing parameters are proposed to achieve better comprehensive performance of bubble-induced slag foaming and molten bath dynamics.展开更多
A flow transition prediction method for calculating effects of Reynolds numbers on aerodynamic characteristics of airfoil is developed,and the accuracy of the method is verified by wind tunnel experiment data and othe...A flow transition prediction method for calculating effects of Reynolds numbers on aerodynamic characteristics of airfoil is developed,and the accuracy of the method is verified by wind tunnel experiment data and other calculation results.On these basics,the infrared thermal imager experiment results of the flow transition in lowspeed wind tunnel and the aerodynamic characteristics experiment results with variable Reynolds number in highspeed wind tunnel are carried out respectively,and compared with the numerical results of helicopter rotor airfoil.Specially,effects of Reynolds numbers on airfoil aerodynamic characteristics by means of flow transition under different working conditions are researched and some meaningful conclusions are obtained.The calculation method,experiment method and results as well as the flow transition analysis conclusions for aerodynamic characteristics can be used for the design of helicopter rotor airfoil,especially for the helicopters under the high altitude and low Reynolds number working conditions.展开更多
A CFD-based numerical model was employed to quantitatively analyze the flow characteristics of double-side-blown gas−liquid flow.Key parameters were extracted,and Spearman correlation analysis was used to quantify the...A CFD-based numerical model was employed to quantitatively analyze the flow characteristics of double-side-blown gas−liquid flow.Key parameters were extracted,and Spearman correlation analysis was used to quantify the relationships among bubble behavior,circulating flow,and liquid oscillations.The results show that periodic bubble behavior under steady injection drives the circulating flow of the liquid on both sides.The asynchronism of bubble behavior on both sides results in the alternation of circulating intensity,which significantly enhances gas−liquid mixing efficiency at certain liquid levels of 200 and 220 mm.Flow patterns of the double-side-blown process are classified into weak circulation,strong−weak alternating circulation,and strong circulation modes based on the influence of circulating flows on the penetration depth.The penetration depth in the strong−weak alternating circulation mode is generally greater than that in the single-side-blown process.The imbalance of circulating intensities on both sides primarily leads to the stable fluctuation in the injecting direction,which reveals the appearance of periodic oscillations in the molten bath.The effect of control parameters such as liquid level and gas flow rate on the liquid oscillations were discussed.展开更多
The multi-pass intermittent local loading process,which features a more flexible processing path,can further enhance the second material distribution during local loading,improve the formability of components,and redu...The multi-pass intermittent local loading process,which features a more flexible processing path,can further enhance the second material distribution during local loading,improve the formability of components,and reduce forming loads.However,the absence of compatible forming equipment makes it difficult to control the constraint in the unloaded zones during the forming process.This difficulty complicates coordination and control of deformation,particularly for asymmetric rib-web components.Additionally,the current implementation involves multi-fire heating,a long process flow,and high energy consumption,which limits the popularization and application of the local loading process.In this study,a new multi-pass local loading hydraulic forming apparatus that can quickly and reliably switch between heavy-load deformation and low-load constraint for different local loading sub-dies was developed.A 10-tonne laboratory prototype was developed,and the forming characteristics during the forming process as well as the response characteristics of the hydraulic system during the multi-pass intermittent local loading of rib-web component were investigated using numerical simulations and physical experiments.Results indicated that,compared to a whole loading process with the same initial geometry of billet,the total forming load(i.e.,the sum of loaded and restrained loads)is reduced by more than 40%with the local loading process,and by nearly 50%with multi-pass local loading.The multi-pass local loading process allows for more effective control of material flow compared to single-pass local loading,leading to improved cavity filling and reduced flow line disturbance.For a large-scale,complex titanium alloy bulkhead,the cavity filling problem was addressed by optimizing the multi-pass local loading path with an unequal thickness billet.The dynamic performance of the multi-pass local loading hydraulic system was found to be robust,with stable pressure transitions during motion and load switching for the sub-die(s).The dynamic characteristic of the hydraulic cylinder when switching from non-moving/unloaded state to a moving/loading state are consistent whether a load is present or not.However,the dynamic characteristics differ when switching from a moving/loading state to non-moving/unloaded state,showing opposite behavior.The developed hydraulic drive mechanism provides a way for implementation of multi-pass local loading without auxiliary operation and extra heating.The results of the study provide a foundation for the industrial production of large-scale,complex components with reduced force requirement and low-energy consumption.展开更多
The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personn...The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personnel from firing artillery within the cab.To investigate the overpressure characteristics of the FFICC,a foreign trade equipment model was used as the research object,and a numerical model was established to analyze the propagation of muzzle blast from the muzzle to the interior of the crew compartment under extreme firing condition.For comparative verification,the muzzle blast experiment included overpressure data from both the flow field outside the crew compartment(FFOCC)and the FFICC,as well as the acceleration data of the crew compartment structure(Str-CC).The research findings demonstrate that the overpressure-time curves of the FFICC exhibit multi-peak characteristics,while the pressure wave shows no significant discontinuity.The enclosed nature of the cab hinders the dissipation of pressure wave energy within the FFICC,leading to sustained high-amplitude overpressure.The frameskin structure helps attenuate the impact of muzzle blast on the FFICC.Conversely,local high overpressure caused by the convex or concave features of the cab's exterior significantly amplifies the overpressure amplitude within the FFICC.展开更多
Extracted natural gas hydrate is a multi-phase and multi-component mixture,and its complex composition poses significant challenges for transmission and transportation,including phase changes following extraction and ...Extracted natural gas hydrate is a multi-phase and multi-component mixture,and its complex composition poses significant challenges for transmission and transportation,including phase changes following extraction and sediment deposition within the pipeline.This study examines the flow and heat transfer characteristics of hydrates in a riser,focusing on the multi-phase flow behavior of natural gas hydrate in the development riser.Additionally,the effects of hydrate flow and seawater temperature on heat exchange are analyzed by simulating the ambient temperature conditions of the South China Sea.The findings reveal that the increase in unit pressure drop is primarily attributed to higher flowvelocities,which result in increased friction of the hydrate flowwithin the development riser.For example,at a hydrate volume fraction of 10%,the unit pressure drop rises by 166.65%and 270.81% when the average inlet velocity is increased from1.0 to 3.0m/s(a two-fold increase)and 5.0 m/s(a four-fold increase),respectively.Furthermore,the riser outlet temperature rises with increasing hydrate flowrates.Under specific heat loss conditions,the flowratemust exceed a minimum threshold to ensure safe transportation.The study also indicates that the riser outlet temperature increases with higher seawater temperatures.Within the seawater temperature range of 5℃ to 15℃,the heat transfer efficiency is reduced compared to the range of 15℃ to 20℃.This discrepancy is due to the fact that as the seawater temperature rises,the convective heat transfer coefficient between the hydrate and the inner wall of the riser also increases,leading to improved overall heat transfer between the hydrate and the pipeline.展开更多
Leveraging big data signal processing offers a pathway to the development of artificial intelligencedriven equipment.The analysis of fluid flow signals and the characterization of fluid flow behavior are of critical i...Leveraging big data signal processing offers a pathway to the development of artificial intelligencedriven equipment.The analysis of fluid flow signals and the characterization of fluid flow behavior are of critical in two-phase flow studies.Significant research efforts have focused on discerning flow regimes using various signal analysis methods.In this review,recent advances in time series signals analysis algorithms for stirred tank reactors have been summarized,and the detailed methodologies are categorized into the frequency domain methods,time-frequency domain methods,and state space methods.The strengths,limitations,and notable findings of each algorithm are highlighted.Additionally,the interrelationships between these methodologies have also been discussed,as well as the present progress achieved in various applications.Future research directions and challenges are also predicted to provide an overview of current research trends in data mining of time series for analyzing flow regimes and chaotic signals.This review offers a comprehensive summary for extracting and characterizing fluid flow behavior and serves as a theoretical reference for optimizing the characterization of chaotic signals in future research endeavors.展开更多
The Lucaogou Formation in Jimsar has a significant development potential due to its massive shale oil resources.Nevertheless,the complex and heterogeneous lithology,coupled with unclear flow mechanisms,poses a challen...The Lucaogou Formation in Jimsar has a significant development potential due to its massive shale oil resources.Nevertheless,the complex and heterogeneous lithology,coupled with unclear flow mechanisms,poses a challenge in effectively predicting its development potential.Therefore,it is crucial to clarify the flow characteristics of shale oil and its controlling factors.In this study,we used a flow simulation experiment to investigate the flow characteristics of different samples under various temperatures and confining stresses and quantitatively evaluated flow characteristics using threshold pressure gradient and total loss of flow rate.Additionally,by combining scanning electron microscopy and mercury intrusion capillary pressure techniques for pore structure characterization,and the relationship between microscopic pore structure and flow parameters was discussed.The findings indicate that rock composition and pore throat structure collaboratively control shale oil flow.Mesopores and macropores primarily develop between dolomite or albite,leading to well-developed pore throat structure with larger average throat radius,lower displacement pressure,and better reservoir quality,enhancing shale oil flowability.Dolomitic siltstone often exhibits these characteristics,making it a favorable lithology for shale oil flow.This study reveals the flow mechanism of shale oil under the action of reservoir physical properties,material compositions,temperatures and confining stresses,summarizes the geological characteristics of advantageous reservoirs.It provides theoretical support for layer selection and efficient development of shale oil reservoirs in the Lucaogou Formation of the Jimsar.展开更多
The turbulent characteristics of the top-blown Laval nozzle and the influence of pressure and Mach number were studied through numerical simulation.With 2.72%error between the results and the empirical formula,the res...The turbulent characteristics of the top-blown Laval nozzle and the influence of pressure and Mach number were studied through numerical simulation.With 2.72%error between the results and the empirical formula,the results are reliable.Nozzle fluid is influenced by pipe structure,causing pressure and density to drop as speed increases.Differences in pressure and velocity between the jet and surrounding gas lead to jet velocity attenuation,flow expansion,deflection,and eddy currents.The optimal top blowing pressure is 0.6 MPa,and the center velocity and width of the jet are 345 m/s and 0.124 m,respectively,at 20De(De is the nozzle exit diameter).It achieves a maximum jet velocity of 456 m/s.The optimal nozzle Mach number is 1.75,with a maximum jet velocity of 451 m/s.At 20D_(e),the jet center velocity is 338 m/s,with a width of 0.12 m.展开更多
The melt stirring in a large copper smelting oxygen bottom-blown furnace is caused by the large amount of gas movement blown in by two rows of oxygen lances.At present,the two rows of oxygen lances provide oxygen of e...The melt stirring in a large copper smelting oxygen bottom-blown furnace is caused by the large amount of gas movement blown in by two rows of oxygen lances.At present,the two rows of oxygen lances provide oxygen of equal strength,and the stirring in the central area of the melt is insufficient,which restricts the efficient progress of the smelting reaction.This study proposes a strong-weak coupling oxygen supply method and establishes an equivalent model based on a large bottom-blown furnace(LBBF)of an enterprise to simulate the bubble characteristics and flow characteristics of the molten pool.The results show that adjusting the flow ratio between the two rows of oxygen lances can create a“strong”and a“weak”coexisting source of disturbance in an LBBF.It is worth noting that when the flow rate ratio of the two rows of oxygen lances is 1.6,the peak velocity generated by the“strong”distur bance source in the molten pool increases by 18.92%,and the disturbance range increases.This method effectively strengthens the stirring in the central area of the molten pool,improves smelting efficiency,and does not produce harmful melt splashes.It provides important guidance for optimizing production practice.展开更多
The construction of bifurcated tunnels is essential to advancing urban infrastructure systems,as they conserve land,reduce carbon emissions,and optimize traffic.However,the bifurcation structure of the parallel conflu...The construction of bifurcated tunnels is essential to advancing urban infrastructure systems,as they conserve land,reduce carbon emissions,and optimize traffic.However,the bifurcation structure of the parallel confluence section of such tunnels poses significant challenges in the design and operation of the tunnel ventilation system,in terms of both the internal and external environment.In this work,the flow and loss characteristics of parallel confluence sections are studied with numerical simulations and model experiments.The influences of the confluence ratio q and the confluence angle O on the flow characteristics and loss mechanisms of the parallel confluence section are revealed theoretically.The results indicate that when q is small,the high-velocity airflow from the mainline entrains the low-speed airflow from the ramp,leading to flow separation at the upper connection between the parallel section and the gradual transition section;when q is large,the high-velocity airflow from the ramp entrains the low-speed airflow from the mainline,resulting in flow separation on the side of the confluence section adjacent to the mainline.Additionally,the mismatch between the airflow ratio Q and cross-sectional area ratio of the mainline tunnel and the ramp prior to confluence enhances the jet entrainment effect,increases the curvature of the streamline,expands the range of the flow separation area,and generates higher confluence loss coefficients|K_(13)|and|K_(23)|of the mainline and the ramp.For small q,|K_(13)|,and|K_(23)|,remain relatively constant with respect toθ,whereas for large q,both|K_(13)|and|K_(23)|decrease asθincreases.Finally,a semi-empirical formula is proposed to predict the loss coefficients for parallel bifurcated tunnels with confluence angles ranging from 5°to 15°.This study provides insights into the aerodynamic behaviour and loss mechanisms in bifurcated tunnels,offering guidelines for enhancing the efficiency of tunnel ventilation systems in tunnel-like underground infrastructure.展开更多
The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and ...The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and conducted to investigate the morphological characteristics and concentration evolution of the sediment plumes under different discharge rates(Q)and initial sediment concentrations(c).Viscosity tests,resuspension tests and free settling tests of the sediment solution with different c values were performed to reveal the settling mechanism of the plume diffusion process.The results show that the plume diffusion morphology variation in flowing water has four stages and the plume concentration evolution has three stages.The larger the Q,the smaller the initial incidence angle at the discharge outlet,the larger the diffusion range,the poorer the stability and the more complicated the diffusion morphology.The larger the c,the larger the settling velocity,the faster the formation of high-concentration accumulation zone,the better the stability and the clearer the diffusion boundary.The research results could provide experimental data for assessing the impact of deep-sea mining on the ocean environment.展开更多
The complex flow characteristics of transverse jet in high-speed crossflow involve several separation regions and multiple shock waves,which make it difficult to capture and precisely predict the flow field state in r...The complex flow characteristics of transverse jet in high-speed crossflow involve several separation regions and multiple shock waves,which make it difficult to capture and precisely predict the flow field state in real time merely by relying on traditional approaches.With the rapid advancement of deep learning technology,its powerful data processing capability offers a fast method for the prediction of the transverse jet flow field.Consequently,a prediction model based on deep learning is established,with the aim of obtaining the flow characteristics of a transverse jet under different freestream and jet conditions.This study segments the complex grid into several individual grids and trains them independently.The trained model can successfully establish the nonlinear mapping relationship between the transverse jet flow field and the input parameters.The prediction accuracy of the established model for the wall pressure under different conditions exceeds 99%,and the established model is also capable of reproducing structures such as shock waves and recirculation zones in the overall flow field,thereby achieving highly precise and efficient prediction of the jet structure and flow information.The results suggest that in contrast to the traditional numerical simulation,this deep learning model demonstrates greater efficiency in predicting the transverse jet flow field.展开更多
The reservoir landslide is typically characterized by high-speed movement of a particle-fluid mixture,and its flow and deposit mechanisms are complex.This paper presents the mechanism of submerged granular column coll...The reservoir landslide is typically characterized by high-speed movement of a particle-fluid mixture,and its flow and deposit mechanisms are complex.This paper presents the mechanism of submerged granular column collapse under different densities ambient fluids based on coupled computational fluid dynamics and discrete element method(CFD-DEM)analysis.Important fluid-particle interaction forces,such as the drag force and the buoyancy,are considered by exchanging interaction forces between the CFD and DEM computations.We focus on the flow and deposit characteristics of submerged granular column collapse,namely the runout distance,the tail end height,the particle velocity,the energy,and deposit morphology,which are analyzed qualitatively and quantitatively.The change in fluid field caused by submerged granular column collapse and the formation of eddies are also discussed.A relatively dense fluid can significantly hinder the motion of granular flow,but can improve the conversion efficiency of kinetic energy from the vertical to the horizontal direction.Moreover,the eddies caused by fluid turbulence erode the surface of the granular pile,which is especially marked in a high-density fluid.The findings can provide vital theoretical support for the flow and deposit characteristics of granular flow under fluid and offer insights for the study of reservoir landslides.展开更多
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 resul...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.展开更多
Some novel techniques of computational fluid dynamics are used to establish a mathematical model for the open diversion channel with two embankments in river blocking.The technique of boundary fitted coordinate syste...Some novel techniques of computational fluid dynamics are used to establish a mathematical model for the open diversion channel with two embankments in river blocking.The technique of boundary fitted coordinate system is used to overcome the difficulties resulting from the complicated shapes of natural river boundaries;the method of alternating direction implicit finite difference scheme is used to solve the partial differential equations in the transformed plane;and the technique of moving boundary is used to deal with the river bed exposed to water surface.This model has been used to predict the flow characteristics in the blocking of the Yangtz river in the Three Gorge Project (TGP).Comparison between the computed and experimental data shows a satisfactory agreement.展开更多
The local chaos characteristics of the time series pressure fluctuations of gas liquid two phase flow in a self aspirated reversed flow jet loop reactor are studied by the deterministic chaos analysis technique. It...The local chaos characteristics of the time series pressure fluctuations of gas liquid two phase flow in a self aspirated reversed flow jet loop reactor are studied by the deterministic chaos analysis technique. It is found that the estimated local largest Lyapunov exponent is positive in all cases and the profile is similar to that of the local fractal dimension in this reactor. The positive largest Lyapunov exponent shows that the reactor is a nonlinear chaotic system. The obvious distribution indicates that the local nonlinear characteristic parameters such as the Lyapunov exponent and the fractal dimension could be applied to further study the flow characteristics such as the flow regine transitions and flow structures of the multi phase reactors.展开更多
The characteristics of the flowfields of a synthetic jet actuator are experimentally investigated with the slot-nozzle driven by the piezoelectric membrane. The particle image velocimetry （PIV） and the hot-wire anem...The characteristics of the flowfields of a synthetic jet actuator are experimentally investigated with the slot-nozzle driven by the piezoelectric membrane. The particle image velocimetry （PIV） and the hot-wire anemometer are utilized to measure the flowfields and the velocity profiles of the actuator with different actuating factors. Analytical results show that pairs of counter-rotating vortices are generated near the nozzle. With the development of the synthetic ject, the synthetic jet rapidly spreads in the slot-width direction; while in the slot-length direction, it contracts firstly and slowly spreads. The centerline velocity distribution has a up-down tendency varying with axial distances, and accelerates to its maximum at z/b= 10. The transverse velocity profile across the slot-width is centro-symmetric and self-similar. However, the velocity profiles across the slot-length are saddle-like near the nozzle. It shows that there are two resonance frequencies for the actuator. If the actuator works with the resonance frequency, the vorticity and the velocity of the synthetic jet are higher than those of other frequencies. Compared with the continuous jet, the synthetic jet shows special flow characteristics.展开更多
As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively high...As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively higher hydraulic loss, which is rarely reported. In order to investigate the influence of blade thickness on the transient flow characteristics of a centrifugal slurry pump with a semi-open impeller, transient numerical simulations were carried out on six impellers, of which the meridional blade thickness from the leading edge to trailing edge varied from 5-10 mm, 5-15 mm, 5-20 mm, 10-10 mm, 10-15 mm, and 10-20 mm, respectively. Then, two of the six impellers, namely cases 4 and 6, were manufactured and experimentally tested for hydraulic performance to verify the simulation results. Results of these tests agreed reasonably well with those of the numerical simulation. The results demonstrate that when blade thickness increases, pressure fluctuations at the outlet of the impeller become severe. Moreover, the standard deviation of the relative velocity in the middle portion of the suction sides of the blades decreases and that at the outlet of the impeller increases. Thus, the amplitude of the impeller head pulsation for each case increases. Meanwhile, the distribution of the time-averaged relative flow angle becomes less uniform and decreases at the outlet of the impeller. Hence, as the impeUer blade thickness increases, the pump head drops rapidly and the maximum efficiency point is offset to a lower flow rate condition. As the thickness of blade trailing edge increases by 10 mm, the head of the pump drops by approximately 5 m, which is approximately 10 % of the original pump head. Futhermore, it is for the first time that the time-averaged relative flow angle is being considered for the analysis of transient flow in centrifugal pump. The presented work could be a useful guideline in engineering practice when designing a centrifugal slurry pump with thick impeller blades.展开更多
To understand the characteristic of circulation flow rate in 250-t RH-TOP vacuum refining process, the 1：4 water model test was established through the bubble behavior and gas holdup in the up-leg to investigate the ...To understand the characteristic of circulation flow rate in 250-t RH-TOP vacuum refining process, the 1：4 water model test was established through the bubble behavior and gas holdup in the up-leg to investigate the effects of different processes and equipment parame- ters on the RH circulation flow rate. With the increases of lifting gas flow rate, liffing bubble travel, and the internal diameter of the up-leg, and the decrease of nozzle diameter, the work done by bubble floatage and the circulation flow rate increase. The expression of circulation flow rate was derived fi＂om the regression analysis of experiment data. Meanwhile, the influences of vacuum chamber pressure and nozzle blockage situation on the circulation flow rate were discussed in detail by the bubble behavior and gas holdup in the up-leg. It is necessary to maintain a certain vacuum chamber liquid level in the molten steel circulation flow. Compared with a nozzle with symmetrical blockage in the up-leg, when a nozzle with non-symmetrical blockage is applied, the lifting gas distribution is non-uniform, causing a great effect on the molten steel circulation flow and making the circulation flow drop largely.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52374317).
文摘Understanding the bubble behaviours and flow characteristics of large-capacity bottom-blowing electric arc furnace(EAF)is crucial for potential exogenous gas-induced slag foaming process and enhancement of molten bath dynamics.A physical model and a 3D gas-slag-steel transient bottom-blowing numerical model of a 150 t EAF were established to investigate the bubble behaviour and flow characteristics throughout the molten steel bath and slag layer under bottom-blowing,with referring to gas flow rate,plug diameter,plug arrangement and injection angle.Results indicate that the average bubble sizes experience increase,dynamic stability and decrease in molten steel bath and then undergo decrease and increase after entering into slag layer for all bottom-blowing modes.The bubble numbers exhibit the opposing trends during the process.Increase in gas flow rate leads to a significant rise in average bubble size but a decrease in number,average dwelling time and the spread area of bubbles in slag layer.Increase in plug diameter causes an opposite impact.The effect of plug arrangement radii on bubbles is almost negligible.Increasing the injection angle results in an increase in bubble size and a decrease in both bubble number and dwelling time in slag layer.The slag foaming potential was discussed referring to the bubble size,number and dwelling time in slag layer.Increase in gas flow rate and plug diameters can significantly enhance the fluids flow through increasing average flow velocity,decreasing mixing time and dead zone ratio of molten bath.Plug arrangement radius and injection angle express nonlinear correlation with average flow velocity and dead zone ratio,and the plug arrangement radius of 0.5R(R represents the radius of bottom circle of EAF model)and injection angle of 15°perform better in enhancing dynamics of molten bath.A group of bottom-blowing parameters are proposed to achieve better comprehensive performance of bubble-induced slag foaming and molten bath dynamics.
文摘A flow transition prediction method for calculating effects of Reynolds numbers on aerodynamic characteristics of airfoil is developed,and the accuracy of the method is verified by wind tunnel experiment data and other calculation results.On these basics,the infrared thermal imager experiment results of the flow transition in lowspeed wind tunnel and the aerodynamic characteristics experiment results with variable Reynolds number in highspeed wind tunnel are carried out respectively,and compared with the numerical results of helicopter rotor airfoil.Specially,effects of Reynolds numbers on airfoil aerodynamic characteristics by means of flow transition under different working conditions are researched and some meaningful conclusions are obtained.The calculation method,experiment method and results as well as the flow transition analysis conclusions for aerodynamic characteristics can be used for the design of helicopter rotor airfoil,especially for the helicopters under the high altitude and low Reynolds number working conditions.
基金financial support for this research work from the National Key Research and Development Program of China(No.2022YFB3304901)。
文摘A CFD-based numerical model was employed to quantitatively analyze the flow characteristics of double-side-blown gas−liquid flow.Key parameters were extracted,and Spearman correlation analysis was used to quantify the relationships among bubble behavior,circulating flow,and liquid oscillations.The results show that periodic bubble behavior under steady injection drives the circulating flow of the liquid on both sides.The asynchronism of bubble behavior on both sides results in the alternation of circulating intensity,which significantly enhances gas−liquid mixing efficiency at certain liquid levels of 200 and 220 mm.Flow patterns of the double-side-blown process are classified into weak circulation,strong−weak alternating circulation,and strong circulation modes based on the influence of circulating flows on the penetration depth.The penetration depth in the strong−weak alternating circulation mode is generally greater than that in the single-side-blown process.The imbalance of circulating intensities on both sides primarily leads to the stable fluctuation in the injecting direction,which reveals the appearance of periodic oscillations in the molten bath.The effect of control parameters such as liquid level and gas flow rate on the liquid oscillations were discussed.
基金the supports of the National Natural Science Foundation of China(Grant No.52375378)。
文摘The multi-pass intermittent local loading process,which features a more flexible processing path,can further enhance the second material distribution during local loading,improve the formability of components,and reduce forming loads.However,the absence of compatible forming equipment makes it difficult to control the constraint in the unloaded zones during the forming process.This difficulty complicates coordination and control of deformation,particularly for asymmetric rib-web components.Additionally,the current implementation involves multi-fire heating,a long process flow,and high energy consumption,which limits the popularization and application of the local loading process.In this study,a new multi-pass local loading hydraulic forming apparatus that can quickly and reliably switch between heavy-load deformation and low-load constraint for different local loading sub-dies was developed.A 10-tonne laboratory prototype was developed,and the forming characteristics during the forming process as well as the response characteristics of the hydraulic system during the multi-pass intermittent local loading of rib-web component were investigated using numerical simulations and physical experiments.Results indicated that,compared to a whole loading process with the same initial geometry of billet,the total forming load(i.e.,the sum of loaded and restrained loads)is reduced by more than 40%with the local loading process,and by nearly 50%with multi-pass local loading.The multi-pass local loading process allows for more effective control of material flow compared to single-pass local loading,leading to improved cavity filling and reduced flow line disturbance.For a large-scale,complex titanium alloy bulkhead,the cavity filling problem was addressed by optimizing the multi-pass local loading path with an unequal thickness billet.The dynamic performance of the multi-pass local loading hydraulic system was found to be robust,with stable pressure transitions during motion and load switching for the sub-die(s).The dynamic characteristic of the hydraulic cylinder when switching from non-moving/unloaded state to a moving/loading state are consistent whether a load is present or not.However,the dynamic characteristics differ when switching from a moving/loading state to non-moving/unloaded state,showing opposite behavior.The developed hydraulic drive mechanism provides a way for implementation of multi-pass local loading without auxiliary operation and extra heating.The results of the study provide a foundation for the industrial production of large-scale,complex components with reduced force requirement and low-energy consumption.
基金supported by the National Natural Science Foundation of China(Grant No.U2341269)。
文摘The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personnel from firing artillery within the cab.To investigate the overpressure characteristics of the FFICC,a foreign trade equipment model was used as the research object,and a numerical model was established to analyze the propagation of muzzle blast from the muzzle to the interior of the crew compartment under extreme firing condition.For comparative verification,the muzzle blast experiment included overpressure data from both the flow field outside the crew compartment(FFOCC)and the FFICC,as well as the acceleration data of the crew compartment structure(Str-CC).The research findings demonstrate that the overpressure-time curves of the FFICC exhibit multi-peak characteristics,while the pressure wave shows no significant discontinuity.The enclosed nature of the cab hinders the dissipation of pressure wave energy within the FFICC,leading to sustained high-amplitude overpressure.The frameskin structure helps attenuate the impact of muzzle blast on the FFICC.Conversely,local high overpressure caused by the convex or concave features of the cab's exterior significantly amplifies the overpressure amplitude within the FFICC.
基金This work was supported by the Ministry of Industry and Information Technology High Tech Ship Special Project(Grant No.CBG3N21-2-6).
文摘Extracted natural gas hydrate is a multi-phase and multi-component mixture,and its complex composition poses significant challenges for transmission and transportation,including phase changes following extraction and sediment deposition within the pipeline.This study examines the flow and heat transfer characteristics of hydrates in a riser,focusing on the multi-phase flow behavior of natural gas hydrate in the development riser.Additionally,the effects of hydrate flow and seawater temperature on heat exchange are analyzed by simulating the ambient temperature conditions of the South China Sea.The findings reveal that the increase in unit pressure drop is primarily attributed to higher flowvelocities,which result in increased friction of the hydrate flowwithin the development riser.For example,at a hydrate volume fraction of 10%,the unit pressure drop rises by 166.65%and 270.81% when the average inlet velocity is increased from1.0 to 3.0m/s(a two-fold increase)and 5.0 m/s(a four-fold increase),respectively.Furthermore,the riser outlet temperature rises with increasing hydrate flowrates.Under specific heat loss conditions,the flowratemust exceed a minimum threshold to ensure safe transportation.The study also indicates that the riser outlet temperature increases with higher seawater temperatures.Within the seawater temperature range of 5℃ to 15℃,the heat transfer efficiency is reduced compared to the range of 15℃ to 20℃.This discrepancy is due to the fact that as the seawater temperature rises,the convective heat transfer coefficient between the hydrate and the inner wall of the riser also increases,leading to improved overall heat transfer between the hydrate and the pipeline.
基金the National Natural Science Foundation of China(22078030)the National Key Research and Development Project(2019YFC1905802,2022YFB3504305)+1 种基金the Joint Funds of the National Natural Science Foundation of China(U1802255,CSTB2022NSCQ-LZX0014)the Key Project of Independent Research Project of State Key Laboratory of Coal Mine Disaster Dynamics and Control(2011DA105287-zd201902).
文摘Leveraging big data signal processing offers a pathway to the development of artificial intelligencedriven equipment.The analysis of fluid flow signals and the characterization of fluid flow behavior are of critical in two-phase flow studies.Significant research efforts have focused on discerning flow regimes using various signal analysis methods.In this review,recent advances in time series signals analysis algorithms for stirred tank reactors have been summarized,and the detailed methodologies are categorized into the frequency domain methods,time-frequency domain methods,and state space methods.The strengths,limitations,and notable findings of each algorithm are highlighted.Additionally,the interrelationships between these methodologies have also been discussed,as well as the present progress achieved in various applications.Future research directions and challenges are also predicted to provide an overview of current research trends in data mining of time series for analyzing flow regimes and chaotic signals.This review offers a comprehensive summary for extracting and characterizing fluid flow behavior and serves as a theoretical reference for optimizing the characterization of chaotic signals in future research endeavors.
基金financially supported by the National Natural Science Foundation of China(No.41972123)the Support Plan for Outstanding Youth Innovation Team in Shandong Higher Education Institutions(No.2022KJ060)。
文摘The Lucaogou Formation in Jimsar has a significant development potential due to its massive shale oil resources.Nevertheless,the complex and heterogeneous lithology,coupled with unclear flow mechanisms,poses a challenge in effectively predicting its development potential.Therefore,it is crucial to clarify the flow characteristics of shale oil and its controlling factors.In this study,we used a flow simulation experiment to investigate the flow characteristics of different samples under various temperatures and confining stresses and quantitatively evaluated flow characteristics using threshold pressure gradient and total loss of flow rate.Additionally,by combining scanning electron microscopy and mercury intrusion capillary pressure techniques for pore structure characterization,and the relationship between microscopic pore structure and flow parameters was discussed.The findings indicate that rock composition and pore throat structure collaboratively control shale oil flow.Mesopores and macropores primarily develop between dolomite or albite,leading to well-developed pore throat structure with larger average throat radius,lower displacement pressure,and better reservoir quality,enhancing shale oil flowability.Dolomitic siltstone often exhibits these characteristics,making it a favorable lithology for shale oil flow.This study reveals the flow mechanism of shale oil under the action of reservoir physical properties,material compositions,temperatures and confining stresses,summarizes the geological characteristics of advantageous reservoirs.It provides theoretical support for layer selection and efficient development of shale oil reservoirs in the Lucaogou Formation of the Jimsar.
基金supported by the National Key Research and Development Project of China(No.2022YFC3902001)the National Natural Science Foundation of China(No.52004340)the Guangxi Innovation-driven Development Project,China(Nos.Gui 2021AA12006 and 2021AB26024)。
文摘The turbulent characteristics of the top-blown Laval nozzle and the influence of pressure and Mach number were studied through numerical simulation.With 2.72%error between the results and the empirical formula,the results are reliable.Nozzle fluid is influenced by pipe structure,causing pressure and density to drop as speed increases.Differences in pressure and velocity between the jet and surrounding gas lead to jet velocity attenuation,flow expansion,deflection,and eddy currents.The optimal top blowing pressure is 0.6 MPa,and the center velocity and width of the jet are 345 m/s and 0.124 m,respectively,at 20De(De is the nozzle exit diameter).It achieves a maximum jet velocity of 456 m/s.The optimal nozzle Mach number is 1.75,with a maximum jet velocity of 451 m/s.At 20D_(e),the jet center velocity is 338 m/s,with a width of 0.12 m.
基金Project(2022YFC3901501)supported by the National Key R&D Program of ChinaProject(U20A20273)supported by the National Natural Science Foundation of China+1 种基金Project(2022JJ10078)supported by the Natural Science Foundation for Distinguished Young Scholars of Hunan Province,ChinaProject(2021RC3005)supported by the Science and Technology Innovation Program of Hunan Province,China。
文摘The melt stirring in a large copper smelting oxygen bottom-blown furnace is caused by the large amount of gas movement blown in by two rows of oxygen lances.At present,the two rows of oxygen lances provide oxygen of equal strength,and the stirring in the central area of the melt is insufficient,which restricts the efficient progress of the smelting reaction.This study proposes a strong-weak coupling oxygen supply method and establishes an equivalent model based on a large bottom-blown furnace(LBBF)of an enterprise to simulate the bubble characteristics and flow characteristics of the molten pool.The results show that adjusting the flow ratio between the two rows of oxygen lances can create a“strong”and a“weak”coexisting source of disturbance in an LBBF.It is worth noting that when the flow rate ratio of the two rows of oxygen lances is 1.6,the peak velocity generated by the“strong”distur bance source in the molten pool increases by 18.92%,and the disturbance range increases.This method effectively strengthens the stirring in the central area of the molten pool,improves smelting efficiency,and does not produce harmful melt splashes.It provides important guidance for optimizing production practice.
基金supported by the National Natural Science Foundation of China(Nos.52408439 and 52478422)the Natural Science Basic Research Program of Shaanxi(No.2023-JC-YB-378),China+3 种基金the Young Talent Fund of Xi'an Association for Science and Technology(No.0959202513050),Chinathe Fundamental Research Funds for the Zhejiang Provincial Universities(No.226-2024-00099),Chinathe Postdoctoral Fellowship Program of China Postdoctoral Science Foundation(No.GZC20241518)the Xi'an Shiyou University Graduate Student Innovation Fund Program(No.YCX2512041),China.
文摘The construction of bifurcated tunnels is essential to advancing urban infrastructure systems,as they conserve land,reduce carbon emissions,and optimize traffic.However,the bifurcation structure of the parallel confluence section of such tunnels poses significant challenges in the design and operation of the tunnel ventilation system,in terms of both the internal and external environment.In this work,the flow and loss characteristics of parallel confluence sections are studied with numerical simulations and model experiments.The influences of the confluence ratio q and the confluence angle O on the flow characteristics and loss mechanisms of the parallel confluence section are revealed theoretically.The results indicate that when q is small,the high-velocity airflow from the mainline entrains the low-speed airflow from the ramp,leading to flow separation at the upper connection between the parallel section and the gradual transition section;when q is large,the high-velocity airflow from the ramp entrains the low-speed airflow from the mainline,resulting in flow separation on the side of the confluence section adjacent to the mainline.Additionally,the mismatch between the airflow ratio Q and cross-sectional area ratio of the mainline tunnel and the ramp prior to confluence enhances the jet entrainment effect,increases the curvature of the streamline,expands the range of the flow separation area,and generates higher confluence loss coefficients|K_(13)|and|K_(23)|of the mainline and the ramp.For small q,|K_(13)|,and|K_(23)|,remain relatively constant with respect toθ,whereas for large q,both|K_(13)|and|K_(23)|decrease asθincreases.Finally,a semi-empirical formula is proposed to predict the loss coefficients for parallel bifurcated tunnels with confluence angles ranging from 5°to 15°.This study provides insights into the aerodynamic behaviour and loss mechanisms in bifurcated tunnels,offering guidelines for enhancing the efficiency of tunnel ventilation systems in tunnel-like underground infrastructure.
基金supported by the Major Project of Hunan Natural Science Foundation,China(No.2021JC0010)the National Natural Science Foundation of China(No.51274251)。
文摘The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and conducted to investigate the morphological characteristics and concentration evolution of the sediment plumes under different discharge rates(Q)and initial sediment concentrations(c).Viscosity tests,resuspension tests and free settling tests of the sediment solution with different c values were performed to reveal the settling mechanism of the plume diffusion process.The results show that the plume diffusion morphology variation in flowing water has four stages and the plume concentration evolution has three stages.The larger the Q,the smaller the initial incidence angle at the discharge outlet,the larger the diffusion range,the poorer the stability and the more complicated the diffusion morphology.The larger the c,the larger the settling velocity,the faster the formation of high-concentration accumulation zone,the better the stability and the clearer the diffusion boundary.The research results could provide experimental data for assessing the impact of deep-sea mining on the ocean environment.
基金co-supported by the National Natural Science Foundation of China(No.12202488)the National Postdoctoral Researcher Program(Grants No.GZB20230985)+1 种基金the Natural Science Program of National University of Defense Technology(No.ZK22-30)the Independent Innovation Science Fund of National University of Defense Technology(No.24-ZZCX-BC-05)。
文摘The complex flow characteristics of transverse jet in high-speed crossflow involve several separation regions and multiple shock waves,which make it difficult to capture and precisely predict the flow field state in real time merely by relying on traditional approaches.With the rapid advancement of deep learning technology,its powerful data processing capability offers a fast method for the prediction of the transverse jet flow field.Consequently,a prediction model based on deep learning is established,with the aim of obtaining the flow characteristics of a transverse jet under different freestream and jet conditions.This study segments the complex grid into several individual grids and trains them independently.The trained model can successfully establish the nonlinear mapping relationship between the transverse jet flow field and the input parameters.The prediction accuracy of the established model for the wall pressure under different conditions exceeds 99%,and the established model is also capable of reproducing structures such as shock waves and recirculation zones in the overall flow field,thereby achieving highly precise and efficient prediction of the jet structure and flow information.The results suggest that in contrast to the traditional numerical simulation,this deep learning model demonstrates greater efficiency in predicting the transverse jet flow field.
基金supported by the National Natural Science Foundation of China(No.51825905).
文摘The reservoir landslide is typically characterized by high-speed movement of a particle-fluid mixture,and its flow and deposit mechanisms are complex.This paper presents the mechanism of submerged granular column collapse under different densities ambient fluids based on coupled computational fluid dynamics and discrete element method(CFD-DEM)analysis.Important fluid-particle interaction forces,such as the drag force and the buoyancy,are considered by exchanging interaction forces between the CFD and DEM computations.We focus on the flow and deposit characteristics of submerged granular column collapse,namely the runout distance,the tail end height,the particle velocity,the energy,and deposit morphology,which are analyzed qualitatively and quantitatively.The change in fluid field caused by submerged granular column collapse and the formation of eddies are also discussed.A relatively dense fluid can significantly hinder the motion of granular flow,but can improve the conversion efficiency of kinetic energy from the vertical to the horizontal direction.Moreover,the eddies caused by fluid turbulence erode the surface of the granular pile,which is especially marked in a high-density fluid.The findings can provide vital theoretical support for the flow and deposit characteristics of granular flow under fluid and offer insights for the study of reservoir landslides.
基金Project (50974033) supported by the National Natural Science Foundation of ChinaProject (N100301002) supported by the Fundamental Research Funds for the Universities, China
文摘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.
文摘Some novel techniques of computational fluid dynamics are used to establish a mathematical model for the open diversion channel with two embankments in river blocking.The technique of boundary fitted coordinate system is used to overcome the difficulties resulting from the complicated shapes of natural river boundaries;the method of alternating direction implicit finite difference scheme is used to solve the partial differential equations in the transformed plane;and the technique of moving boundary is used to deal with the river bed exposed to water surface.This model has been used to predict the flow characteristics in the blocking of the Yangtz river in the Three Gorge Project (TGP).Comparison between the computed and experimental data shows a satisfactory agreement.
文摘The local chaos characteristics of the time series pressure fluctuations of gas liquid two phase flow in a self aspirated reversed flow jet loop reactor are studied by the deterministic chaos analysis technique. It is found that the estimated local largest Lyapunov exponent is positive in all cases and the profile is similar to that of the local fractal dimension in this reactor. The positive largest Lyapunov exponent shows that the reactor is a nonlinear chaotic system. The obvious distribution indicates that the local nonlinear characteristic parameters such as the Lyapunov exponent and the fractal dimension could be applied to further study the flow characteristics such as the flow regine transitions and flow structures of the multi phase reactors.
文摘The characteristics of the flowfields of a synthetic jet actuator are experimentally investigated with the slot-nozzle driven by the piezoelectric membrane. The particle image velocimetry （PIV） and the hot-wire anemometer are utilized to measure the flowfields and the velocity profiles of the actuator with different actuating factors. Analytical results show that pairs of counter-rotating vortices are generated near the nozzle. With the development of the synthetic ject, the synthetic jet rapidly spreads in the slot-width direction; while in the slot-length direction, it contracts firstly and slowly spreads. The centerline velocity distribution has a up-down tendency varying with axial distances, and accelerates to its maximum at z/b= 10. The transverse velocity profile across the slot-width is centro-symmetric and self-similar. However, the velocity profiles across the slot-length are saddle-like near the nozzle. It shows that there are two resonance frequencies for the actuator. If the actuator works with the resonance frequency, the vorticity and the velocity of the synthetic jet are higher than those of other frequencies. Compared with the continuous jet, the synthetic jet shows special flow characteristics.
基金Supported by National Natural Science Foundation of China(Grant No.51239005)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively higher hydraulic loss, which is rarely reported. In order to investigate the influence of blade thickness on the transient flow characteristics of a centrifugal slurry pump with a semi-open impeller, transient numerical simulations were carried out on six impellers, of which the meridional blade thickness from the leading edge to trailing edge varied from 5-10 mm, 5-15 mm, 5-20 mm, 10-10 mm, 10-15 mm, and 10-20 mm, respectively. Then, two of the six impellers, namely cases 4 and 6, were manufactured and experimentally tested for hydraulic performance to verify the simulation results. Results of these tests agreed reasonably well with those of the numerical simulation. The results demonstrate that when blade thickness increases, pressure fluctuations at the outlet of the impeller become severe. Moreover, the standard deviation of the relative velocity in the middle portion of the suction sides of the blades decreases and that at the outlet of the impeller increases. Thus, the amplitude of the impeller head pulsation for each case increases. Meanwhile, the distribution of the time-averaged relative flow angle becomes less uniform and decreases at the outlet of the impeller. Hence, as the impeUer blade thickness increases, the pump head drops rapidly and the maximum efficiency point is offset to a lower flow rate condition. As the thickness of blade trailing edge increases by 10 mm, the head of the pump drops by approximately 5 m, which is approximately 10 % of the original pump head. Futhermore, it is for the first time that the time-averaged relative flow angle is being considered for the analysis of transient flow in centrifugal pump. The presented work could be a useful guideline in engineering practice when designing a centrifugal slurry pump with thick impeller blades.
文摘To understand the characteristic of circulation flow rate in 250-t RH-TOP vacuum refining process, the 1：4 water model test was established through the bubble behavior and gas holdup in the up-leg to investigate the effects of different processes and equipment parame- ters on the RH circulation flow rate. With the increases of lifting gas flow rate, liffing bubble travel, and the internal diameter of the up-leg, and the decrease of nozzle diameter, the work done by bubble floatage and the circulation flow rate increase. The expression of circulation flow rate was derived fi＂om the regression analysis of experiment data. Meanwhile, the influences of vacuum chamber pressure and nozzle blockage situation on the circulation flow rate were discussed in detail by the bubble behavior and gas holdup in the up-leg. It is necessary to maintain a certain vacuum chamber liquid level in the molten steel circulation flow. Compared with a nozzle with symmetrical blockage in the up-leg, when a nozzle with non-symmetrical blockage is applied, the lifting gas distribution is non-uniform, causing a great effect on the molten steel circulation flow and making the circulation flow drop largely.
