Flow Field Distribution Research Articles

Research on flow, heat transfer, and solidification characteristics of flow distribution process in the twin-roll casting

Twin-roll casting (TRC) has seen a significant interest in recent years due to its short process, low energy consumption, and low emission. The research included both numerical simulation and experimental validation to examine the flow and temperature field distribution of the TRC process. The “U-shaped” buffer groove is identified as beneficial for maintaining a stable liquid level distribution in the molten pool through comparison with various flow distributor structures. The solidified billet shell dispersion around the casting roller in the molten pool is observed to undergo three distinct stages: stable growth, thickness fluctuation, and rapid growth. The inclusion of two circular side outlets, each with a diameter ranging from 8 to 10 mm, proves advantageous in maintaining a stable distribution of the liquid level within the molten pool. The edge outlet size ranges from 7 to 9 mm, and ensuring a U-shaped buffer groove width/flow distribution of 1.25–1.58 aids in enhancing casting stability.

Research on uncertainties in fuel centrifugal pump based on prediction and reconstruction of internal flow field

Geometric machining errors in the blade profile and variable operating conditions in the extreme operating environment are primary factors leading to the uncertainties in pump performance. This paper presents an analysis of uncertainties of fuel centrifugal pumps by modeling the geometry uncertainty in blade machining based on the Karhunen–Loève (KL) expansion and using a polynomial chaos expansion (PCE) model. First, the geometric uncertainty in the blade machining is described by the KL expansion in three sections and a stochastic simulation of the blade geometry is performed. Then, a PCE surrogate model is trained based on the least angle regression method and validated by the bootstrap method to quantify the uncertainties of performance indices. Finally, the influence mechanism and relative importance of each input uncertainty parameter are investigated using a quasi-Monte Carlo simulation method. The results show that the KL expansion of the blade profile uses the random vector perturbation superposition of three stream surface, achieving the dimensional reduction in the blade machining error. The PCE surrogate model, trained with a dataset of 3 × 106 sample points, exhibits excellent fit, and the R-squared and adjusted R-squared for head coefficient and efficiency are both above 80%. The variance of parameter control points of the reconstructed flow field is less than 0.002. The uncertainties in both operating conditions and parameters have an influence on the distribution of the global flow field, while the influence of the uncertainty in machining error on the global flow field mainly concentrates on the power-generating positions of the blade.

Experiments for control of boundary layer transition by plasma actuators

Plasma flow control technology is a new type of active flow control technology, and this paper carries out certain research on the basic principle of plasma flow control technology and its application on the wing model. The paper introduces the theory of plasma discharge and analyzes how plasma can control the flow field. A parallel dielectric barrier discharge plasma exciter is then designed and tested by using the Particle Image Velocimetry (PIV) technique to investigate the spatial flow field distributions of single-stage and three-stage actuators, and the mechanism of jet generation by the actuator is analyzed. Finally, the plasma actuator was utilized to control flow separation on a super-zero-boundary airfoil, and the oil droplet interferometric method was used to study the actuator’s role in controlling boundary layer transition. The experiment revealed that increasing the actuator discharge voltage can further reduce wall drag and more effectively delay the transition. Under the given conditions of a head-on angle of 6° and the incoming wind speed of 20 m/s, a two-stage actuator’s continuous discharge parameter was set to an output voltage of 12 kV and an output frequency of 4.7 kHz. The results showed that the transition position can be delayed by 13%, indicating the effectiveness of the actuator’s jet effect in enhancing the stability of the boundary layer flow.

A mean flow velocity estimation scheme based on flow field characteristics and distribution point optimization for carbon monitoring in coal-fired power plants: A numerical study

CO2 online monitoring provides a method to obtain carbon emissions by directly quantifying the flue gas flow rate and CO2 concentration. However, significant flow rate measurement errors arise due to the complexity of turbulence in large-diameter stacks. To address the issue, this study utilizes turbulence numerical simulation combined with mean velocity estimation error analysis to investigate the flow field of typical stacks in coal-fired power plants. The simulation results demonstrated that the evolution of turbulence exaggerates velocities. The flow field exhibits stable turbulence characteristics in a single-introduced stack, while in the double-introduced stack, the flow field dynamically evolves due to asymmetric collisions and abrupt expansions. Furthermore, the effects of load and temperature on the estimation error of flow velocity are established. The optimum monitoring height, the ideal chord angle and the stepped number of deployment points based on the log-linear method are determined. Within the single-introduced stack, a correction factor is introduced and a corresponding formula is established that links estimation errors with monitoring heights. This resulted in a dramatic reduction of the maximum estimation error from 14% to 0.3%. Finally, the systematic and simplified optimization scheme for estimating mean flow velocity is summarised, which provides a powerful reference for flow rate measurement for online CO2 monitoring in coal-fired power plants.

Investigation on mixing characteristics of rotating detonation combustor with convergent inlet

Mixing characteristics play an important role on the operational process of rotating detonation combustor (RDC). In this paper, a series of numerical calculations were conducted to analyze the influence of injection diameter, injection position, reactant mass flow rate, and equivalence ratio on mixing characteristics. Mixing performance parameters and total pressure loss in combustor dome and ignition zone were analyzed in detail. The findings indicated that all four injection conditions had significant influence on mixing characteristics, among which injection position was the most significant factor. When injection position was in convergent section, the mixing characteristics were better than those in ignition section. Reducing the fuel diameter gradually improved mixing characteristics, but also increased total pressure loss. The change of reactant mass flow rate had a minimal effect on mixing characteristics. As equivalence ratio decreased, mixing characteristics decreased and total pressure loss decreased. In addition, the comparative analysis also showed that penetration depth of hydrogen had an impact on flow field disturbance and distribution of return region, which led to the difference in mixing characteristics. When hydrogen was injected into the convergent structure section where air flow velocity did not reach sonic speed and was in acceleration phase, total pressure loss would be effectively reduced in combustor dome.

Numerical Study of the Force Characteristics and Flow Field Patterns of a Cylinder in the Internal Solitary Wave

The density of the ocean is unevenly distributed along the depth direction, showing a stratified structure. When there is an external disturbance, large-scale internal solitary waves are easily generated. The internal solitary waves are bounded by the intermediate pycnocline, and the currents in the upper and lower layers will flow in opposite directions. This generates strong shear forces that threaten the safety of marine structures. In this paper, the flow field distribution characteristics of a cylinder under the action of internal solitary waves at different scales are analyzed as a research object. The whole cylinder is discretized into 40 regions, and the horizontal force applied to each section of the cylinder is extracted. The force characteristics of the cylinder are analyzed. It is concluded that the pressure is the main factor determining the magnitude of the total combined force. In addition, the paper extracts the main flow structures from the modal decomposition point of view and explains the reasons affecting the force behavior of the cylinder.

Numerical simulation of physical field during different ultrasonic power assisted casting of 7085 aluminum alloy

High‐energy ultrasound has the effect of purifying the aluminum (Al) melt and improving the uniformity of temperature and flow field distribution. In this paper, a finite element numerical model of ultrasonic‐assisted casting of 7085 Al alloy melt was established, and the changes of acoustic pressure field, temperature field and flow field in the solidification process of alloy melt with different ultrasonic power were investigated. The numerical simulation results show that the thickness of the 7085 Al melt mushy zone decreases by 89 mm, 97 mm, 108 mm, 114 mm and 99 mm, respectively, compared without ultrasonic (WNU) when the ultrasonic power was 150 W, 350 W, 550 W, 750 W and 950 W. The area of the alloy mushy zone increases by 38.1%, 43.5%, 61.0%, 206.5% and 45.6%, respectively. According to numerical simulation results, when the ultrasonic power was 750W, it had the best effect on improving the macroscopic physical field, increasing the mass and heat transfer rate in the center of the Al melt. Meanwhile, the experimental results of industrial melting and casting of 7085 large‐scale Al alloy ingots were basically consistent with the numerical simulation, which provided technical support for ultrasonic‐assisted fabrication of large‐scale 7085 Al alloy ingots.This article is protected by copyright. All rights reserved.

Study on the Flow Field Distribution in Microfluidic Cells for Surface Plasmon Resonance Array Detection.

This research is dedicated to optimizing the design of microfluidic cells to minimize mass transfer effects and ensure a uniform flow field distribution, which is essential for accurate SPR array detection. Employing finite element simulations, this study methodically explored the internal flow dynamics within various microfluidic cell designs to assess the impact of different contact angles on flow uniformity. The cells, constructed from Polydimethylsiloxane (PDMS), were subjected to micro-particle image velocimetry to measure flow velocities in targeted sections. The results demonstrate that a contact angle of 135° achieves the most uniform flow distribution, significantly enhancing the capability for high-throughput array detection. While the experimental results generally corroborated the simulations, minor deviations were observed, likely due to fabrication inaccuracies. The microfluidic cells, evaluated using a custom-built SPR system, showed consistent repeatability.

Enhanced heat transfer for subway linear motor through underbody flow regulation

The low-speed flow, restricted tunnel environment, and degraded motors have resulted in a serious challenge in the underbody equipment of subway trains, where overheating of multiple longitudinally aligned linear induction motors is one of the most urgent challenges to be resolved. In the face of this problem, the flow field distribution of a 4-car formation subway train is investigated. Two deflector installation designs are proposed to regulate the underbody flow using the passive flow control method to enhance the heat dissipation of motors. The influence of deflector installation is analyzed through an experimentally verified conjugated heat transfer numerical method. The results showed that the installation of deflectors can significantly enhance the longitudinal underbody flow. On the one hand, the deflector can effectively enhance the momentum exchange between underbody flow and the surrounding undisturbed flow field. On the other hand, the deflectors can break the large lateral vortices, such that the flow resistance along the longitudinal direction is reduced. Besides, the deflectors can also reduce the size of the wake behind the motor. As a result, the increased incoming flow rate ahead of motors effectively alleviated the overheating issue. The enhancement of heat transfer between different deflector installation designs was compared. It was found that the vertical edge of deflectors should be installed as close to the lateral edge of the subway car as possible. The maximum temperature of motors has been reduced by 9 % according to the installation design proposed in this study. The outcomes of this study can also provide theoretical guidance as well as engineering solutions for the cooling design of bottom heat sources and other similar overheating devices in thousands of railway trains with exposed underbody compartment. The convection enhancement around the heating devices can be realized by the surrounding flow field regulation method proposed in this study.

Analytical solution to boundary layer flow and convective heat transfer for low Prandtl number fluids under the magnetic field effect over a flat plate

AbstractThe present study aims to quantify the flow field, flow velocity, and heat transfer features over a horizontal flat plate under the influence of an applied magnetic field, with a particular emphasis on low Prandtl number fluids. Nonlinear partial differential expressions can be incorporated into the ordinary differential framework with the use of appropriate transformations. This research utilizes the variational iteration method (VIM) to approximate solutions for the system of nonlinear differential equations that define the problem. The objective is to demonstrate superior flexibility and broader application of the VIM in addressing heat transfer issues, compared to alternative approaches. The results obtained from the VIM are compared with numerical solutions, revealing a significant level of accuracy in the approximation. The numerical findings strongly suggest that the VIM is effective in providing precise numerical solutions for nonlinear differential equations. The analysis includes an examination of the flow field, velocity, and temperature distribution across various parameters. The study found that improving temperature patterns, velocity distribution, and flow dynamics were all positively impacted by increasing the Prandtl numbers. As a result, this leads to the thickness of the boundary layer to decrease and improves heat transfer at the moving surface. Thus, the convection process becomes more efficient. When the strength of the magnetic field is increased, the velocity of the fluid decreases. This observation aligns with expectations since the magnetic field hampers the natural flow of convection. Notably, the convection process can be precisely controlled by carefully applying magnetic force.

Response of sediment microbial communities to the flow effect of the triangular artificial reef: A simulation-based experimental study

Artificial reefs (ARs), as an important tool for habitat restoration, play significant impacts on benthic microbial ecosystems. This study utilized 16S rRNA gene sequencing technology and computational fluid dynamics (CFD) flow simulation to investigate the effects of flow field distribution around ARs on microbial community structure. The results revealed distinct regional distribution patterns of microbial communities affected by different hydrodynamic conditions. Flow velocity and flow regime of water in sediment-water interface shaped the microbial community structure. The diversity and richness in R–HF were significantly decreased compared to other five regions (p < 0.05). At the phyla and OUT levels, most abundant taxa (1>%) showed an enrichment trend in R–HB. However, more than half of differentially abundant taxa were enriched in R–HB, which was significantly correlated with organic matter (OM). Bugbase phenotypic predictions indicated a low abundance of the anaerobic phenotype in R–HF and a high abundance of the biofilm-forming phenotype in R–HB.

Numerical simulation study on noise pollution of the pressurized gas system in pumped storage power station

To Investigate the noise pollution caused by pneumatic whistling during the blowdown operation of a pressurized gas storage system in a pumped storage power station, the flow field and sound field distribution of the gas storage tank under blowdown operation are analyzed in detail through full-channel unsteady numerical simulation of the gas storage tank and its supporting facilities. Subsequently, a comprehensive analysis of the noise issue in the gas cylinder was conducted. While investigating the mechanism of noise generation based on the distribution of noise intensity, the precise location of the noise source was pinpointed, providing a reference for the stability research of the exhaust pressurized water system.

Oscillatory instability of magneto-convection during the melting of non-Newtonian ferromagnetic nano-enhanced phase change materials at low Rayleigh number

This work complements mechanism of the oscillatory instability of magneto-convection in the process of melting heat transfer controlled by magnetic field at low Rayleigh number (Ra), aiming to provide a theoretical basis for improving the stability of energy storage system and melting manufacturing process. A latent heat storage cavity unit exposed in uniform magnetic field is designed to reveal the magnetic-controlled heat transfer in solid–liquid phase change process. The volume average method is used to describe porous media composite nano-enhanced phase change materials in latent heat unit. Special attentions are paid to the key parameters of Magnetic number (Mn) and Ra, and coupling flow heat transfer mechanism of magnetic force and natural convection effect is numerically studied. The evolution stages of different flow patterns are divided according to the Kelvin force, vorticity, velocity, flow field and isotherm distributions of characteristic points. Main results show that the magnetic field-modulated phase change process at low Ra can be divided into three stages, of which the second stage is characterized by periodic oscillations. Increasing Mn at fixed Ra accelerates the second stage of oscillatory convection heat transfer coming earlier and promotes melting. When Mn increase to 5 × 106, the full melting time is reduced to the greatest extent, resulting in 11.6 % reduction in heat storage but 17.4 % increase in heat storage efficiency. Three mechanisms of magnetic forced convection coupled with natural convection are found during the increase of Ra: synergistic (Ra < 2 × 103), antagonistic (2 × 103≤ Ra < 1 × 104), and natural convection-dominated (Ra = 1 × 104). Finally, the mode distribution map of Ra-Mn regulation is obtained, in which the unstable transformation mechanism of steady-state, periodic oscillation and chaotic oscillation heat transfer in the melting process under the control of magnetic field is described.

A local scour model for single pile on silty seabed considering soil cohesion (SedCohFOAM): Model and validation

In this study, the sediment transport two-phase flow model named SedFOAM is expanded to include soil cohesion, creating a new model named SedCohFOAM within OpenFOAM. The local scouring flume experiment involving a pile on silty seabed and sandy seabed is conducted in a curved flume. Due to the influence of cohesion, the scouring depth at different locations on sandy seabed is 15%–18% greater than that on silty seabed. Observations from this experiment informed the analysis of force balance, wherein the agglomerated silt particles are modeled as large singular entities and the cohesive force is treated as a downward influence that keeps the aggregated particles stationary. Meanwhile, the experimental outcomes are utilized to validate the accuracy of the SedCohFOAM model. The numerical findings demonstrated that SedCohFOAM can simulate the flow field distribution around the pile, variations in seabed shear stress, and alterations in seabed surface morphology. Compared with the SedFOAM model, the SedCohFOAM model has a significantly reduced simulation error in simulating scour on silty seabed. When comparing the cross-sectional profiles of the scour holes derived from the flume experiments with those simulated by SedCohFOAM, it was observed that the ultimate-equilibrium scour depth predicted by the model is consistently lower, but the scour radius in the numerical simulations is larger. The deviation from the experimental results is nearly within 8%, while when the flow velocity is high, the simulation error of the simulated scouring depth behind the pile and the scouring radius in front of pile is amplified.

Simulation study on hydraulic characteristics of Changzhou fishway based on FLUENT

Guangxi Changzhou Fishway is the first significant water conservancy project above the mouth of the Pearl River and also the first large fishway independently designed in China. It is the primary migration channel for six kinds of state-level protected fish, such as Chinese sturgeon and a typical vertical slit fishway. This paper takes the Changzhou fishway as the research object, based on the theory of fluid mechanics, and adopts the method of combining theoretical analysis, experimental research, and numerical simulation to study the flow field of different water depths in the pond. The analysis results show that the upper water flow has a larger resting area than the lower water flow, and the fishway has a rich flow field distribution and can produce “S” shaped meandering flow characteristics. The research results provide some reference for the design of vertical fishways.

Simulation on stirling reverse osmosis desalination power system

In this article, a new power system based on the Stirling engine and hydraulic free piston engine is proposed to provide power for reverse osmosis (RO) desalination. First, the design of the Stirling free piston RO desalination power system was carried out, and the size parameters of the main structures such as the regenerator, heater, cooler, power piston, and valve distribution piston were obtained. A physical model was established to simulate the process of the Stirling engine driving the RO desalination power system based on finite element CFD. The flow field distribution cloud map and output power of the Stirling engine were analyzed. The results indicate that the gas motion of the Stirling engine is stable, and the entire power system can operate normally.

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

Baffleless coils can operate as continuous oscillatory flow reactors to produce pharmaceutical products where process intensification is intended. A method to evaluate mixing performance and its impact on reaction conversion is residence time distribution (RTD) analysis. Liquid macromixing in a long baffleless coil reactor (L = 24 m, dt = 4.57 mm) at ranges of oscillation amplitude (11.75–58.75 mm), frequency (0–3.68 Hz), and net flow rate (30–120 g⋅min−1) was investigated based on measured RTDs fitted to the skewed normal distribution model. The impact of operating conditions on the RTD was supported by analyzing the liquid flow field derived from CFD simulations. The RTD variance under different oscillation conditions suggests a near plug flow pattern, although deviations from ideality such as skewness and long tailing were always observed. The model parameters, along with the RTD variance, were correlated to the operating conditions lumped in an oscillatory Dean number that used the flow amplitude as characteristic length (Deox). Values of Deox varied between 150 and 11000, and the RTD variance at the different net flow rates was minimized for 300 < Deox < 600, as also evidenced from the minimum cross-sectional variance of the simulated time-averaged axial velocity profile. Normalizing the data allowed comparison to similar coil studies with different geometrical dimensions and operating conditions, leading to generalized correlations for the RTD model parameters. Finally, chemical conversion was assessed for first- and second-order single phase reactions at different Damköhler numbers using the segregation and maximum mixedness micromixing models combined with the fitted RTDs. The performance of the coil remained consistent with a plug flow reactor despite its departures from ideal flow.

Application of UVAS and TDLAS-based multi-combustion-parameter diagnosis using computerized tomography

Fossil fuel combustion is the main source of mechanical power and will be accompanied by the production of a large number of toxic and harmful substances, such as NO and CO. In this study, Computed Tomography-Tunable Diode Laser Absorption Spectroscopy (CT-TDLAS) and Computed Tomography-Ultraviolet Absorption Spectroscopy (CT-UVAS) were used to establish a multi-combustion-parameter diagnosis system. A corrected H2O absorption database was applied by the wavelength at 1388 nm and 1343 nm. The spectra at 2325 nm were used to establish the CO absorption database. NO absorption database at 214 nm/226 nm was established by UVAS. The nonlinear least squares with the polynomial fitting method was applied to CT reconstruction. A custom CT cell was designed to fix the fiber and probes of the CT-TDLAS and CT-UVAS, and its rationality was evaluated by the Sum of squared difference (SSD) and Zero-mean normalization cross-correlation (ZNCC) through the comparison between CFD simulation and CT reconstruction. In the experiment, the CT reconstruction of the temperature, H2O, and CO showed significant distribution profile differences between two premixed flames. The NO detection function was demonstrated by standard NO gas, and the maximum average relative error was 4.99 %. The results show that the multi-combustion-parameter diagnosis system can measure the temperature, H2O, CO, and NO distribution of the combustion flow field at high frequency. The multi-combustion-parameter diagnosis system will assist with research and diagnosis on controlling NO generation and promoting combustion efficiency.

Chitosan-Based Grafted Cationic Magnetic Material to Remove Emulsified Oil from Wastewater: Performance and Mechanism

In order to remove high-concentration emulsified oil from wastewater, a chitosan-based magnetic flocculant, denoted as FS@CTS-P(AM-DMC), was employed in this present study. The effects of factors including the magnetic flocculant dose, pH values, and coexisting ions were investigated. A comparative dosing mode with the assistance of polyacrylamide (PAM) was also included. The evolution of floc size was studied using microscopic observation to investigate the properties of flocs under different pH values and dosing modes. Particle image velocimetry (PIV) and extended Deryaguin–Landau–Verwey–Overbeek models were utilized to illustrate the distribution and velocity magnitude of the particle flow fields and to delve into the mechanism of magnetic flocculation. The results showed that FS@CTS-P(AM-DMC) achieved values of 96.4 and 74.5% for both turbidity and COD removal for 3000 mg/L of simulated emulsified oil. In the presence of PAM, the turbidity and COD removal reached 95.7 and 71.6%. In addition, FS@CTS-P(AM-DMC) demonstrated remarkable recycling and reusability performances, maintaining effective removal after eight cycles. The strength and recovery factors of magnetic flocs without PAM reached 69.3 and 76.8%, respectively. However, with the addition of PAM, they decreased to 46.73 and 51.47%, respectively. During the magnetophoretic processes, FS@CTS-P(AM-DMC) and oil droplets continuously collided and aggregated, forming three-dimensional network aggregates. Moreover, the magnetic floc generated a swirling motion, and the residual emulsified oil droplets could be further captured. Emulsified oil droplets were primarily removed through charge neutralization under acidic conditions. Under neutral and alkaline conditions, magnetic interactions played a major role in magnetic flocculation.

Experimental Study on the Sedimentation Performance of an Arc-Plate Linear Sedimentation Tank

To examine the influence of plate shapes and quantities on the sedimentation performance of a linear sedimentation tank, experimental research was conducted using tanks featuring five distinct plate structures. The findings reveal that when subjected to an inflow rate ranging from 60 to 100 m3/h and with median particle sizes of 571.110 μm and 162.254 μm, for sediment particles in water containing sediment, the flow field distribution in the arc-plate sedimentation tank facilitates the effective settling of sediment particles. Comparative analyses indicate that incorporating eight arc plates in the sedimentation tank, as opposed to an equal number of inclined plates, results in a notable reduction in surface sediment concentration within the plate region, ranging from approximately 8 to 34%. Additionally, the mass percentage of sediment particles with sizes less than 0.05 mm at the tank bottom increases by about 5–7%. Moreover, in comparison to tanks lacking plates and those equipped with four arc plates, the surface sediment concentration experiences a significant decrease, ranging from approximately 33% to 60% and 18% to 44%, respectively. Concurrently, the mass percentage of sediment particles with sizes less than 0.05 mm shows an increase of about 25–32% and 10–20%. The arc-plate sedimentation tank exhibits superior sedimentation efficiency with an inflow rate of 60 m3/h and the installation of eight arc plates. Additionally, the study concludes that increasing the number of plates and reducing the inflow rate enhance sediment settling. The research findings offer valuable insights for the design and advancement of sedimentation tanks.