Numerical Simulation Of Flow Field Research Articles

Numerical Simulation of Flow Fields and Sediment-Induced Wear in the Francis Turbine

Based on the solid–liquid two-phase flow model and the Realizable k-ε Turbulence model, numerical simulations of the sediment–water flow in the flow components of the turbine were conducted. The distribution of sediment-induced wear within the turbine was obtained by analyzing the sediment volume fraction (SVF) and the erosion rate. The results revealed that sediment-induced wear on the stay and guide vanes was primarily distributed along the water inlet edge of the stay and guide vanes. For the runner blades, wear was predominantly localized along the water inlet edge and near the lower ring. The sediment-induced wear patterns on these flow components were found to be consistent with the sediment volume fractions (SVFs) on their surfaces.

Influence of the number of guide vane blades on the energy conversion characteristics of gas-liquid mixing pumps

Abstract To investigate the optimal number of guide vanes for peak performance efficiency in a mixing pump, this study employs a self-engineered gas-liquid mixing pump to the principal subject of analysis. adopts SST κ -ω turbulence model, Euler multiphase flow model and SIMPLEC algorithm, and conducts three-dimensional flow field numerical simulation under five operating conditions with the number of guide vane of the gas-liquid mixing pump as 5, 7, 9, 11, 13, 15, and 17, and the volume gas content as 10% to 50%, respectively. Volume gas content were 10% ∼ 50% of the five conditions for three-dimensional flow field numerical simulation, the experimental findings indicate that: with an increase in the number of guide vane blades, the efficiency of the pump’s secondary impeller varies in a cubic function relationship. When the gas content at the inlet is between 10% and 20%, efficiency is highest with 9 blades. When the gas content at the inlet is between 30% and 50%, efficiency is highest with 15 blades. Additionally, when there are 9 blades, the head of the secondary impeller reaches its maximum at different gas contents at the inlet.

Numerical Simulation of Flow Field, Distribution of Bubbles, and Inclusions in Slab Continuous Casting Mold under Electromagnetic Braking Assisted with High‐Temperature Quantitative Velocity Measurement

Numerical Simulation of Flow Field, Distribution of Bubbles, and Inclusions in Slab Continuous Casting Mold under Electromagnetic Braking Assisted with High‐Temperature Quantitative Velocity Measurement

Numerical Simulation of Flow Field around Jacket Foundations on Flat-Bed and Equilibrium Scour Bathymetry

Numerical Simulation of Flow Field around Jacket Foundations on Flat-Bed and Equilibrium Scour Bathymetry

Numerical and experimental investigation of 2-thiazoline-2-thiol and nitrotetrazolium blue chloride compound as levelers for through-hole copper electroplating

Leveler is essential in the electroplating process of the through-hole (TH), the adsorption characteristics of which are strongly influenced by the aspect ratios of the THs. However, only a single kind of leveler usually appears in the most frequently performed THs’ filling electrolyte, which is highly possible to limit the electrolyte's capability to fill THs and improve the copper film properties. In this paper, two levelers, 2-Thiazoline-2-Thiol (T1) and Nitrotetrazolium Blue chloride (NBT), with significant molecular weight differences, were combined to fill THs with multiple ARs. The interactions among the leveler compounds and other additives become the primary factor controlling the THs electroplating process, which was systematically investigated through a combination of flow field numerical simulation and electrochemical measurements. T1 presents a weaker inhibition effect and is more sensitive to convection than NBT, which also exhibits a convection-enhanced inhibition effect with other additives. The convection of the electrolyte in the THs center continuously decreases with the ARs, guiding to the increasing electroplating rate at the THs center, high throwing power (TP) of 141%, and flawless filling of the THs with ARs of 4.75:1∼1.9:1 in 2.5 h. The copper film on the surface maintains extremely high flatness and low thickness.

Research on the influence of system drainage holes on the head loss of water transmission systems

Abstract To ensure the structural safety of the thin lining structure of the tailwater tunnel, this study used three-dimensional flow field numerical simulation technology to conduct an in-depth analysis of the drainage holes set along the tunnel body, to evaluate the impact of drainage holes on the overall and local head loss of the tunnel under different system layout types. It aims to provide scientific theoretical support and practical reference for engineering design and achieve more efficient and stable tunnel hydraulic operation conditions.

Enhancement of aerodynamic performance of axial compressors utilizing natural aspiration through optimized casing circumferential slot

This paper presents results of aerodynamic enhancement of axial compressors utilizing optimum natural aspiration through a circumferential slot made within the casing wall upstream the rotor blades row. The method of investigation is based on numerical simulation of flow field. Geometries of the slot walls were optimized to find the maximum stall margin and pressure ratio of the compressor. The optimum case is accompanied by boosting more momentum within the blades tip region through the slot. Consequently, tip leakage vortex flow weakens and compressor stability margin increases. Final results showed that in comparison to the untreated casing, the optimum geometry of the slot causes the total pressure ratio and stall margin to increase by 4.2% and 3%, respectively. This state-of-the-art technique is simple and economic which can be easily implemented in practical cases while the compressor is exposed to commencement of flow instabilities in the forms of the rotating stall or surge phenomena.

Recommendations on setup in simulating atmospheric gravity waves under conventionally neutral boundary layer conditions

Wind farm-induced atmospheric gravity waves have been the subject of recent research as they can impact wind farm performance. Pressure variations associated with gravity waves can contribute to the global blockage effect and wind farm wake recovery. Therefore, accurate numerical simulation of flow fields, where wind-farm-induced gravity waves may be produced, is important. Three main considerations in such simulations are the overall domain size, the use of Rayleigh damping near domain boundaries to dampen gravity waves, and advection damping at the inlet to prevent spurious oscillations. Often these considerations are treated ad hoc rather than systematically. This work aims to test and extend the systematic modelling of internal gravity waves proposed in a preliminary investigation to modelling of both internal and trapped gravity waves. The preliminary study identifies the length scales to set the domain and damping layer sizes and the time scale to configure the Rayleigh damping coefficient but under linearly stratified conditions. Large eddy simulations of flow through a wind farm canopy are performed under conventionally neutral boundary layer (CNBL) conditions to test the validity of proposed setups for CNBL conditions. Background atmospheric parameters, such as Froude number (Fr), inversion height (Hi ), and inversion layer Froude number (Fri ) control most of the atmospheric gravity wave characteristics. We validated for CBNL conditions that the effective wavelengths of the internal gravity waves are the correct length scale to configure the domain size and damping layer thickness. Likewise, the optimum damping coefficient to dampen the internal gravity waves relates to the free atmosphere’s buoyancy frequency or buoyant perturbations’ time scale. We infer that the damping coefficient in the inversion layer may relate to the inversion buoyancy frequency to effectively dampen the trapped gravity waves. Moreover, the advection damping length is linked to the horizontal wavelength of the trapped gravity waves in the inversion layer to prevent spurious waves at the inlet by retaining wave energy accumulation.

Current Efficiency Comparison of Two Types of Rare Earth Electrolytic Cells: Flow Field Numerical Simulation Analysis and Experimental Investigation

Current Efficiency Comparison of Two Types of Rare Earth Electrolytic Cells: Flow Field Numerical Simulation Analysis and Experimental Investigation

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.