Numerical Simulation Of Flow Field Research Articles

Investigation on the influence of seal clearance leakage on the rotating stall characteristics for a centrifugal pump

The occurrence and development of centrifugal pump rotating stall is closely related to disturbance in the incoming flow. The seal clearance leakage is an inherent disturbance in the impeller incoming flow of centrifugal pumps. In order to investigate the seal clearance leakage influence on the rotating stall characteristics, the flow field numerical simulation of a centrifugal pump under rotating stall flow conditions with and without seal clearance are carried out. It is found that under the 0.4Q0 rotating stall condition with seal clearance leakage, the “λ” special shaped high-velocity region distribution along the blade leading edges are strengthened, which lead to larger scale of stall vortices. And the periodicity of the separation vortex evolution is more obvious under the condition with leakage. For a specific stall vortex development process, at the initial format stage, there is a notable disturbance characteristic of medium frequencies band that of 2–3 times the rotation frequency in the pressure fluctuation near the blade leading edges, which is significantly different from that under the condition without leakage. The vorticity analysis shows that this disturbance is closely related to the leakage induced vortices. Affected by the seal clearance leakage disturbance, the stall rotating propagation frequency is reduced from 0.143 times the impeller rotational frequency to 0.103 times. Meanwhile, the fluctuation intensity in the impeller channels is greatly enhanced. Therefore, by judging the special fluctuation frequencies, regularity, and intensity trend in the monitoring signal, it can not only be used to guide the safe operation of centrifugal pumps under off-design conditions but also serve as the basis for judging the wear of the seal, which has important practical significance.

Numerical Simulation of Flow Field Over a Sharp-Tipped Double Cone at High Speed

The flowfield over a sharp-tipped double cone axisymmetric configuration is carried out by solving time dependent axisymmetric laminar compressible Navier-Stokes equations for freestream Mach number range of 2.0 - 6.0. The fluid dynamics equations are discretized in spatial coordinates using integral formulation in conjunction with finite volume method which reduces the governing equations to semi-discretized ordinary differential equations. Temporal integration is performed employing multistage Runge-Kutta time-stepping scheme. A local time step is used to achieve steady-state solution. The numerical computation is carried out on a mono-block with structured grids. The flowfield features over the sharp-tipped double cone configuration such as conical shock wave, separation region, separation and reattachment shock wave and bow shock wave in the cone region, expansion fan, and recirculation flow in the base region are well captured at Mach number 3 and 6 which are identical to the Edney VI type shock interaction. The velocity vector, Mach contours plots and variations of surface pressure coefficient along the sharp-tipped double cone configuration are analyzed at various Mach numbers. The fore-body aerodynamic drag is calculated employing computed pressure distribution. The paper presents the influence of the freestream Mach number on the flows with shock interactions over the sharp-tipped double cone geometry.

Numerical Simulation of Magnetic Field and Flow Field of Slab under Composite Magnetic Field

A kind of composite magnetic field for flow control in slab mold is proposed, in which an electromagnetic stirring (EMS) is carried out near the meniscus and an electromagnetic braking (EMBr) is carried out near the outlet of the submerged entry nozzle (SEN), simultaneously. The yoke for the EMS and the EMBr is made independent from each other, with a ruler type for the EMBr. A three-dimensional model of the magnetic field calculation is established. The simulation results show that the magnetic induction intensity generated with the EMS mainly concentrates in the EMS area. The magnetic induction intensity generated with the EMBr has a large component in the EMS results, which has little effect on the flow of this area. Based on the composite magnetic field calculation results, the three-dimensional numerical simulation of the flow field is carried out, and the flow field obtained is compared to that without the magnetic field but with the EMS and the EMBr only, respectively. The results show that under the composite magnetic field, EMBr and EMS can play their respective roles well under certain conditions, the impact of the jet flow on the narrow face is reduced, and the stirring beneath the meniscus is intensified.

Generation mechanism of lack of fusion in X70 steel welded joint by fully automatic welding under steep slope conditions based on numerical simulation of flow field

X70 pipeline steel is butt welded by fully automatic welding at 25° slope, and the characteristic information of welding process is collected. A 3D transient heat and mass transfer model of weld pool is established. This model was verified by means of the shape of the weld pool and the two-dimensional shape of the weld, and then, the flow field of the fully automatic welding process under steep slope conditions was simulated to clarify the mechanism of the lack of fusion defect. The results show that the welding arc is deflected when it stays on both side walls of the groove. The slope makes the liquid metal tend to gather at the lower groove. When gravity plays a leading role in the flow of the molten pool, some liquid metal begins to flow out from the lower groove to the front end, resulting in an overflow phenomenon. The generation of overflow phenomenon and arc deflection cause the formation of a “void zone” at the structure mutation position in front of the groove. In the welding process, the liquid metal tends to flow to the side walls for heat transfer under various thermal effects, and forms a large range of eddy current at the side walls. This has a positive effect on sidewall melting. In addition, the effect of surface tension at the lower groove is more obvious than that at the upper groove, and the trend of upward flow along the side wall is stronger, so it is difficult for the high-temperature liquid metal in the arc center to flow to the “void area” located at the bottom of the side wall of the lower groove. Therefore, the bottom of the lower groove is more likely to cause lack of fusion defect.

150USRT Class R-513A Refrigerant Two-Stage Centrifugal Compressor Design Point and Separation Point Flow Field Simulation Analysis

This study used computational fluid dynamics for low greenhouse effect refrigerant (R-513A) simulation analysis in the two-stage 150 USRT class oil-free centrifugal refrigerant compressor using integrated part load value (IPLV) and internal flow field. The compressor rotor speed and mass flow rate for the IPLV working conditions with various loads were planned using Stage 1 and Stage 2 simulations, respectively. The performance and flow field numerical simulation analyses for the two-stage centrifugal compressor is discussed. This study used Ansys-CFX software for numerical simulation analysis and the conservation form of a 3D steady-state Navier–Stokes equation set with the finite volume discretization method for computation. The computing mode produced better computing efficiency and flexible mesh setting using the k-omega (k-ω) model, which has better computational performance in the near wall boundary layer and low Reynolds number flow field (used as the turbulence model) for simulation. The R-513A refrigerant property setting was calculated using the Soave–Redlich–Kwong gas equation. This study discusses the shaft work, pressure ratio, and isentropic efficiency and also describes the main research findings with the meridional pressure, isentropic efficiency contour maps, and flow field velocity vector diagrams. According to the numerical simulation results, in Stage 1 and Stage 2 simulations, the isentropic efficiency produced the highest numerical results in the 75% load case, which are 88.19% and 89.06%, respectively. The isentropic efficiency decreased to 75.93% and 82.26%, respectively, in the 25% load case. The flow field velocity vector diagram shows that in the 25% load case, there was back-flow field distribution near the impeller shroud. The compressor performance was also analyzed.

Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle

A model of a submerged angular cavitation nozzle is established, which consists of a contraction part, parallel middle part, and expansion part. Based on the CFD technique, a numerical simulation of the flow field of the submerged cavitation nozzle is carried out, in which a multiphase mixture model, cavitation model, and renormalization group (RNG) k-ε turbulence model are applied. Considering the influence of mixture density on cavitation, the effects of the inlet contraction part, parallel middle part, and outlet expansion part on the velocity and vapor volume fraction are studied. The numerical simulation results show that the mixture density is essential in the cavitation jet. When the nozzle diameter d is fixed, the designed angular cavitation nozzle with contraction angle α = 13.5°, parallel middle part length Ld = 3d, expansion part length Le = 4d, and expansion angle β = 60° can effectively bring out cavitation. A cavitation cloud is produced near the rigid wall of the outlet expansion section and diffuses in a vortex ring shape. Optimizing the nozzle structure can improve the cavitation effect of the nozzle. The feasibility of this model is verified by relevant experimental data.

Numerical simulation and analysis of flow field in directional solidification equipment

Directional solidification equipment is an efficient purification tool. In this paper, the geometric model was established based on the equipment, and the numerical simulation of the flow field in equipment was realized through the RNG turbulence model, flow volume function model, and the multiple reference system method. In order to improve the fluid velocity, turbulent kinetic energy, and uniform distribution of circulating flow in the flow field, the effects of different crucible structures, process parameters, and structure of rotator on the flow field were analyzed. The research results show that the round bottom crucible has a faster flow velocity in front of the wall, and the flow velocity distribution is uniform. When the rotator is located in the center of the flow field, flow velocity and turbulent kinetic energy are distributed more evenly. Controlling the rotational speed to reduce the air entering the liquid phase is conducive to preventing solidification from being oxidized. Considering the thickness of the solidified layer, increasing the blade length can help increase the fluid velocity.

Numerical simulation of flow field and residence time of nanoparticles in a 1000-ton industrial multi-jet combustion reactor

In this work, by establishing a three-dimensional physical model of a 1000-ton industrial multi-jet combustion reactor, a hexahedral structured grid was used to discretize the model. Combined with realizable k–ε model, eddy-dissipation-concept, discrete-ordinate radiation model, hydrogen 19-step detailed reaction mechanism, air age user-defined-function, velocity field, temperature field, concentration field and gas arrival time in the reactor were numerically simulated. The Euler–Lagrange method combined with the discrete-phase-model was used to reveal the flow characteristics of particles in the reactor, and based on this, the effects of the reactor aspect ratios, central jet gas velocity and particle size on the flow field characteristics and particle back-mixing degree in the reactor were investigated. The results show that with the decrease of aspect ratio in the combustion reactors, the velocity and temperature attenuation in the reactor are intensified, the vortex phenomenon is aggravated, and the residence time distribution of nanoparticles is more dispersed. With the increase in the central jet gas velocities in reactors, the vortex lengthens along the axis, the turbulence intensity increases, and the residence time of particles decreases. The back-mixing degree and residence time of particles in the reactor also decrease with the increase in particle size. The simulation results can provide reference for the structural regulation of nanoparticles and the structural design of combustion reactor in the process of gas combustion synthesis.

Structure Optimization Research Based on Numerical Simulation of Flow Field in Ammonia-Based Wet Sintering Flue Gas Desulfurization

Although more and more desulfurization equipment has been put into use in sintering plants, how to effectively remove sulfur dioxide from sintering flue gas in a desulfurization tower is still a great challenge in China. The desulfurization tower, as a critical part, needs further improvement and optimization. Therefore, based on the numerical simulation of the flow field of the ammonia-based wet desulfurization tower for sintering flue gas, ANSYS CFX is applied to conduct structural optimization research. Comparing the flow field distribution under different structure conditions, the results show that the flue gas distribution of the dual inlet tower is more uniform than that of the single inlet tower. The designed baffle not only effectively blocks the entry of the spray slurry, but also improves the flue gas distribution; the deflector with its simple structure, convenient operation, and stepped distribution installed in the entrance section can improve the uniformity of the flow field distribution. Based on the comprehensive analysis, these optimized structures are recommended in the design of an ammonia-based wet sintering flue gas desulfurization tower. This work not only develops a simulation of the desulfurization tower but also provides practical structures.

Withdrawn: Research progresses in flow field of close-coupled atomizer and atomization mechanism

With the development of part manufacturing technology, many fields, such as medical treatment, military industry, machine and three-dimensional (3D) printing, propose increasingly higher requirements on performances of metal/alloy powder. Low oxygen content, accurate alloy composition, small particle size and high particle sphericity become characteristics of high-quality powder. With high atomization efficiency, low oxygen content in powder and high cooling rate, the close-coupled gas atomized powder preparation technology is an ideal choice to prepare high-quality powder. Nevertheless, powder preparation technology based on close-coupled gas atomization is a complicated process with mutual coupling effects of multiple-phases flows. However, the atomization mechanism still is not revealed fully yet. Close-coupled gas atomized powder preparation technology is facing with great challenges in mass preparation of high-quality powders at a low cost. It is expected to improve close-coupled gas atomized powder preparation technology and even achieve breakthroughs in atomizing principle. For this reason, this study summarized atomizer structure, gas atomization flow field test technology and gas flow field numerical simulation thoroughly according to existing associate studies. Moreover, the gas atomization mechanism of close-coupled atomizer was analyzed. Finally, further deep studies on atomizing characteristics and atomization mechanism of close-coupled vortical loop slit atomizer were prospected and several research directions were proposed. This paper summarized atomizer structure, gas atomization flow field test technology and gas flow field numerical simulation. Moreover, the gas atomization mechanism of close-coupled atomizer was analyzed. Further deep studies on atomizing characteristics and atomization mechanism of close-coupled vortical loop slit atomizer were prospected and several research directions were proposed.

Numerical simulation of hydraulic characteristics of an upstream wing submerged T-shaped groyne

Groynes can prevent erosion of banks. In this study, an upstream wing submerged T-shaped groyne (ST) was proposed. The hydraulic characteristics and the bed elevation of the proposed groyne were compared with those of a T-shaped groyne. Under the consideration of the flow field measurements of a 60° bend movable bed experiment, a digital terrain after the bed development was obtained, using laser scanning technology. The flow field numerical simulation was performed with this digital terrain as the boundary. The results demonstrated that in comparison with the T-shaped groyne, the depth-averaged velocity of ST near the groyne head decreased by 14%, the length of the back-flow zone behind the ST was shortened by about 36%, and the streamlines near the wing of the groyne were smoother. Additionally, the scour depth in the range of the groyne increased by about 0.2 times the approaching flow depth H.

The Whole Process CFD Numerical Simulation of Flow Field and Suspended Solids Distribution in a Full-Scale High-Rate Clarifier

To further reduce the contents of phosphorus and suspended solids (SS) in the effluent, the high-rate clarifier is adopted by some wastewater treatment plants (WWTPs) to upgrade their processes. However, due to the complex phosphorus species and unclear hydraulic characteristics after the addition of the high-rate clarifier, the removal efficiencies of total phosphorus and the optimization strategies of SS removal remain unclear. The high-rate clarifiers are mainly composed of the mixing zone and the settling zone. Only the hydraulic characteristics of the mixing zone have been studied. It is necessary to focus on the hydrodynamics of the settling zone to understand the sedimentation process and pollutant removal mechanism in depth. Therefore, this study focused on the whole process of high-rate clarifier of the Wuhan Nantaizi Lake WWTP in China. The distributions of flow velocity and SS in the full-scale high-rate clarifier were simultaneously simulated by the solid-liquid two-phase whole process computational fluid dynamics (CFD) model which was established in this study. The simulated results of the developed CFD model were in good agreement with the experimental data obtained in the high-rate clarifier. The normalized standard error was less than 7.66%. The overall flow velocities in the settling tank were much smaller than that in the reaction tank. After the fluid passed through the diversion effect of the overflow wall and the under-through channel, the overall kinetic energy loss was relatively large. Meanwhile, the residence time of fluid in the settling tank was longer than that in the reaction tank. The sludge sedimentation happened at the edge of the settling tank due to the vertical angle between the plug-flow fluid and the outlet. The successful construction of the CFD model could lay the foundation for the next step of the high-rate clarifier optimization operation and research on pollutant removal.

Inactivation of B. cereus spores in whole milk and almond milk by serpentine path coiled tube UV-C system: Numerical simulation of flow field, lipid peroxidation and volatiles analysis

A novel continuous thin-film (1.59 mm) serpentine path coiled tube (SPCT) UV system operating at 254 nm wavelength was designed and compared with flow field distribution of whole milk with helical path coiled tube (HPCT) UV system using computational fluid dynamics. The results revealed efficient velocity magnitude distribution at serpentine bend geometric locations of the SPCT UV system. Further in this study, we evaluatedBacillus cereusSpores inactivation in whole milk (WM) and almond milk (AM) using the developed SPCT UV system. Experimental data showed that > 4 log reduction of spores was achieved after six and ten passes of WM and AM at a flow rate of 70 and 162 mL/min, respectively. The bio-dosimetry method was used to verify the delivered reduction equivalent fluence (REF) and reported as 33 ± 0.73 and 36.5 ± 1.9 mJ/cm2. We noticed no significant effect on lipid oxidation and volatiles profile (p > 0.05) up to delivered REF of 60 mJ/cm2. This study demonstrated that high levels of inactivation ofB. cereusspores could be feasible with minimal impact on product quality by UV-C processing of dairy and non-dairy opaque scattering fluids.

Numerical Simulation of Flow Field, Bubble Distribution and Solidified Shell in Slab Mold under Different EMBr Conditions Assisted with High-Temperature Quantitative Velocity Measurement

The flow field, bubble distribution and solidified shell in slab mold are numerically simulated with large eddy simulation (LES) under different electromagnetic braking (EMBr) conditions, assisted with high-temperature quantitative velocity measurement. The calculated velocities on the mold surface are in good agreement with the measured values of the industrial experiment at high temperature with the rod deflection method under different EMBr conditions and different argon flow rates, which verifies the correctness of the model. After EMBr is applied, the flow velocity on the surface of the mold decreases. With EMBr, the velocity on the mold surface first increases and then decreases with the increase in argon flow rate. When the argon flow rate is 10 L·min−1, the jets at the side ports of the submerged entry nozzle (SEN) become disordered, and the liquid level fluctuation near the SEN wall intensifies, which increases the risk of slag entrainment and slag layer breaking and the risk of argon bubbles being captured. When the argon flow rate is 6 L·min−1, the velocity and fluctuation on the mold surface can be significantly reduced by use of double-ruler EMBr; the impact of the jet on the narrow face of the mold is obviously restrained; and the solidified shell thickness increases.

Numerical Simulation of Flow Field Optimizing the Rotating Segregation Purification of Silicon for SoG-Si

In order to improve the preparation efficiency of high-purity silicon, a new method of rotary segregation purification has been developed to prepare polysilicon. Numerical simulation based on ANSYS19.0 software and water model experiments were used to study the distribution of flow field and optimize the impurity removal process. A numerical simulation model suitable for rotating interface is established. The simulation result is in good agreement with the water model experiment. A vortex flow is found in the middle of the mold when the mold insertion depth is 90 mm. The vortex is conducive to the thinning of the impurity enrichment layer at the solid–liquid interface. With the mold insertion depth increases from 90 to 170 mm, two vortex flows appear in the middle and bottom of the mold, respectively. Moreover, setting the mold rotation rate at 100 rpm can contribute to a more stable flow field and a higher melt flow velocity. When the diffusion layer thickness is less than 0.1 mm, the impurity segregation coefficient can approach close to its equilibrium segregation coefficient, indicating that impurity segregation be effectively enhanced by increasing the rotation rate of mold, strengthening the effect of solidification rate and increasing the rotational speed. Industrial tests were carried out at the 100 kg level. The result shows that the rotary segregation method and equipment can achieve the removal of very low impurity in silicon (99.999 pct), and SoG-Si (99.9999 pct) was obtained. This method provides a new way for silicon purification, and it is believed that better results can be obtained through continuous improvement.

Parallel Numerical Simulation of Complex Unsteady Multi-Component Three-Dimensional Flow Field of Nonequilibrium Chemical Reaction

Parallel Numerical Simulation of Complex Unsteady Multi-Component Three-Dimensional Flow Field of Nonequilibrium Chemical Reaction

A method for numerical simulation of mode transition process of compression system of variable cycle engine based on throttle valve model

In order to study the aerodynamic characteristics of the compression system of a variable-cycle engine during its mode transition, a low-order model was established based on the throttle valve theory to describe the throttle characteristics of the mode selection valve at its different opening degrees. The model was applied to the outlet of a double-bypass variable-cycle fan in the form of characteristic boundary. A 3D low-order hybrid computational model was established for the numerical simulation of flow fields in the mode transition process of the compression system. The calculation accuracy and effectiveness of the throttle valve model were verified by comparing its calculation results with those of the 3D valve model. The simulation method was further applied to the prediction and analysis of the fan performance variation during the single and double bypass mode transitions of the variable-cycle fan. The simulation results show that: the throttle coefficient, which represents the throttle intensity, has something to do only with the flow area ratio of the valve but has nothing to do with its angle. Therefore, the throttle valve model is universal for valves with different motion angles; the throttle valve model can accurately predict the variation trend of the aerodynamic characteristics of the fan in all stages of the mode transition process. Compared with the 3D valve model, the prediction error of the pressure ratio of the fan in all stages is less than 1.93%, and the efficiency error is less than 1.05%. In the valve closing process, the second-stage rotor performance changes more dramatically, and the first-stage rotor performance changes with lag.

Numerical simulation of flow field of molten steel in the caster mould

In order to analyse the molten steel flow in the mould, a 2D model including the mould and the SENwas established. The fluctuation of molten steel on the meniscus of the mould and the steel flow velocity field in the mould and nozzle were analyzed. The calculation results show that: (1) the steel flow velocity field in the mouldwas the highest in the nozzle area. When liquid steel flows out of the SEN, its flow velocity decreases gradually. (2) There were three regions flow in the mould. There were two reflux areas outside the nozzle, the dividing line is the free surface, and the other reflux area is 0.2 m∼0.9 m. The liquid steel within 0.9 m∼1.5 m flows vertically downward. (3) The free surface near the nozzle is high, while the free surface away from the nozzle is low. The free surface is the lowest at 0.1 m and the highest at 0.06 m.

Numerical simulations of flow field and flow-induced vibration in rectangular channel with single cylinder

A vortex street structure in a narrow channel can not only enhance the mixing efficiency of the turbulence, but also cause flow-induced vibration. In this study, a rectangular channel with a single cylinder was used as the research object. The generation and influence factors of the turbulent vortex street structure in the channel and the flow-induced vibration of a cylindrical structure caused by the vortex street structure were numerically studied. First, based on the experimental data and numerical results, the accuracy of the numerical method used in this study for the flow field calculation and fluid–structure coupling calculation was verified. Second, the influence of the rod–wall gap size (W/D) on the vortex street structure formation and turbulent mixing efficiency was studied based on the validated numerical method. Finally, the flow-induced vibration of a cylindrical structure caused by a vortex street structure in a narrow channel was numerically studied using a weak coupling algorithm, and the influence of W/D on the vibration characteristics of the cylindrical structure was obtained. The results showed that an RSM-ε anisotropic turbulence model could accurately capture the vortex street in a narrow channel. The value of W/D had a significant effect on the formation of the vortex street structure. When W/D is greater than 1.150, the vortex street structure disappears. The presence of vortex street structure can significantly enhance the mixing efficiency of turbulent flow. The vortex street structure also caused the buckling of the cylinder in the normal direction of the narrow channel.

Modeling and numerical simulation of flow field in three types of standard new design cyclone separators

In this paper, numerical simulation of flow field in three types of standard new design cyclone separators namely 1D2Dn, 1D3Dn and 2D2Dn are investigated. In these standard cyclones, the length of cylindrical top part of the body is equal to 1, 1 and 2 times of the body diameter, respectively; and the length of the cylindrical bottom part is 2, 3 and 2 times of the body diameter. The new design cyclone is based on the idea of improving cyclone collection efficiency and pressure drop by increasing the vortex length. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). Results show that among the three standard new design cyclones, cyclone 2D2Dn has the highest efficiency followed by 1D3Dn one with about only 2% lower efficiency. Cyclone 1D2Dn possesses the lowest efficiency among all. Similarly, the highest pressure drop occurs in cyclone 2D2Dn. Cyclones 1D3Dn and 1D2Dn followed 2D2Dn one with a marked difference of about 20%. In result section, the details of the flow field including velocity, pressure contours, turbulence, velocity vectors and particle trajectory will be presented.