Computational Fluid Dynamics Theory Research Articles

Numerical Simulation of Combustion in 35 t/h Industrial Pulverized Coal Furnace with Burners Arranged on Front Wall

Coal-fired industrial boilers should operate across a wide range of loads and with a higher reduction of pollutant emission in China. In order to achieve these tasks, a physical model including two swirling burners on the front wall and boiler furnace was established for a 35 t/h pulverized coal-fired boiler. Based on Computational Fluid Dynamics (CFD) theory and the commercial software ANSYS Fluent, mathematical modeling was used to simulate the flow and combustion processes under 75% and 60% load operating conditions. The combustion characteristics in the furnace were obtained. The flue gas temperature simulation results were in good agreement with experimental data. The simulation results showed that there was a critical distance L along the direction of the furnace depth (x) and Hc along the direction of the furnace height (y) on the burner axis. When x < L, the concentration of NO decreased sharply as the height increased. When y < Hc, the NO concentration decreased sharply with an increase in the y coordinate, while increasing dramatically with an area-weighted average gas temperature increase in the swirl combustion zone. This study provides a basis for optimizing the operation of nitrogen-reducing combustion and the improvement of burner structures.

Research on the Influence of External Parameters of Fan-Type Nozzle on Water Jet Performance

At present, high-pressure water jet technology occupies a very important position in the automobile washing industry. Some automatic washers cannot meet the washing requirements in the washing process due to unreasonable arrangement of nozzles on their spray rods. Based on the theory of computational fluid dynamics (CFD), the internal and external flow field model of the nozzle are established in this paper. Fluent is used to simulate and analyze the flow field, and the external parameters of the nozzle on the side spray bar of the automatic automobile washer are optimized. The simulation results show that after the nozzle and the normal line of the automobile surface are inclined at a certain angle, the target surface is affected not only by normal striking force but also by tangential pushing force, which makes stains easier to remove. The washing effect is the best when the nozzle is inclined 30° to the normal line of the automobile surface. Increasing the nozzle inlet pressure will increase the dynamic pressure on the automobile surface, but the increase of dynamic pressure will decrease after increasing to a certain pressure. The inlet pressure has little effect on the area covered by water jet. The reasonable matching results of jet angle, nozzle spacing, and nozzle distance from the automobile surface (target distance) obtained by numerical simulation can not only make the automobile surface completely covered and cleaned but also ensure less jet interference and no waste of water from adjacent nozzles. The above research conclusions can provide a basic theoretical basis for the optimal design of automatic automobile washing.

Effects of ventilation on leakage and diffusion law of gas pipeline in utility tunnel

The gas pipeline in the utility tunnel locates at an underground closed space. Once the gas leaks, the accident consequence will be more serious. Therefore, it is very important to study the effect of ventilation on leakage and diffusion of the gas pipeline in the utility tunnel. This paper takes the gas pipeline in the utility tunnel in Songjiang District of Shanghai as the study object. Based on the computational fluid dynamics (CFD) theory, a simulation model of gas pipeline in the utility tunnel is established, and the scenarios of gas leakage and diffusion under different ventilation velocities and ventilation outlet’s sizes are simulated respectively. The results show that: (1) Gas diffusion time has an exponential relationship with both ventilation velocity and side length of ventilation outlet. (2) Alarm time on the downwind side in the gas tunnel has a linear relationship with both ventilation velocity and ventilation outlet’s size. (3) Gas volume ratio has a power function relationship with both ventilation velocity and side length of ventilation outlet. (4) Gas average concentration has an exponential relationship with ventilation velocity and a logarithmic relationship with side length of ventilation outlet, and the effects of ventilation velocity and ventilation outlet’s size on the gas concentration along the distance are similar. (5) In practical engineering, it is an optimal selection that the ventilation velocity is between (5 m/s, 7 m/s) and the side length of ventilation outlet is between (1 m, 1.25 m).

The Minimum Wave Resistance of Hull Form Design Method Based on CFD Method

To reduce the resistance of the ship in actual navigation, a hull form optimization design method for minimum wave resistance is proposed. A numerical wave tank of regular waves is established based on the CFD (Computational Fluid Dynamics) theory. Overlapping grid technology is adopted to mesh the hull form and free surface. The new hull offsets are generated by using the parameters of modified function as design variables. The geometric expression and reconstruction of optimized hull form is determined through the three-dimensional CAD (Computer Aided Design) modeling technology. The displacement limit was used as the basic constraint, and other additional constraints were considered; nonlinear programming quadratic line search algorithm was used to set up a mathematical model of hull form optimization on the ISIGHT platform. The optimization calculations of Wigley hull form and surface ship DTMB5415 are carried out. Compared with the parent hull, the wave resistance of the optimized hull form is significantly reduced, and the feasibility of this method is confirmed. The research results can provide technical support for the development of "green ship"design.

Numerical Investigation on Generation and Propagation Characteristics of Offshore Tsunami Wave under Landslide

Tsunamis induced by the landslide will divide into a traveling wave component propagating along the coastline and an offshore wave component propagating perpendicular to the coastline. The offshore tsunami wave has the non-negligible energy and destruction in enclosed basins as fjords, reservoirs, and lakes, which are worth studying. The initial submergence condition, the falling height and sliding angle of slider, are important reference indexes of damage degree of landslide and may also matter at that of the landslide-induced tsunami. Depending on the fully coupled model, the effects of them on the production and propagation of the tsunami were considered in the study. Since the slider used was semi-elliptic, the effect of the ratio of the long axis to the short axis was also analyzed. According to the computational fluid dynamics theory, a numerical wave tank was developed by the immersed boundary (IB) method; besides, the general moving-object module of slide mass was also embedded to the numerical tanker. The results indicate that the effects of the squeezing and pushing of the slider on water produce a naturally attenuated wave at the front of the wave train, and the attenuation becomes more serious with the increase in the initial submersion range of the slider. The effects of the vertical movement of the slider cause the increase in the amplitude of the back of the wave train. As the falling height increases, the large wave height increases when the slider is initially submerged and decreases when it is not initially submerged, except for the accidental elevation of that at smaller falling heights. The results also indicate that the hazard of the subaerial landslide-induced tsunami is greater under a small or large falling angle, and that of the partial subaerial and submarine landslide-induced tsunami is greater under a small falling angle. With the increase in the ratio of the long axis to the short axis, the total induced wave energy decreases and the shape of the wave train proportionally reduces, while the wave propagation mode does not change.

Numerical simulation and engineering application of multistage atomization dustfall at a fully mechanized excavation face

To explore the effect of atomization and dustfall at a fully mechanized excavation face with a multistage external spray, numerical simulation of an airflow-dust field and airflow-droplet field was carried out using the theory of computational fluid dynamics (CFD). The migration and distribution of dust and droplet particles with airflow were analyzed, and the effect of multistage atomization was explored via numerical simulation and field measurements. The results show that dust mass concentrations up to 2000 mg/m3 are generated near the head and gradually diffuse over 35 m on the downwind side of the roadheader, and the average droplet concentration exceeds 0.2 kg/m3. The first, second and third stages of external spray settle a large portion of the high dust concentration. The fourth stage of external spray settles the dust at the point of transfer, and the fifth stage of external spray forms a water curtain at the back of the roadway to minimize dust diffusion. The field measurement shows that the multistage external spray dust suppression system can effectively reduce the dust concentration at the 33down03 fully mechanized face, with dust removal rates for total dust and respirable dust of 76.04% and 84.3%, respectively. The dustfall effect is remarkable.

Research on overflow diffusion characteristics of dredger

Dredging engineering is widely used in port and waterway construction, water conservancy facilities construction, environmental protection dredging, land reclamation, subsea tunnel excavation and deep-sea mining, among which drag suction dredger is an important tool for dredging operation. During the process of its construction, the mud overflow process is an important link to realize the mud treatment of excavation. According to the actual engineering conditions, the loading and overflow process is an important part of the treatment of excavated slurry. With the increasing requirements of environmental protection, the related ecological pollution caused by dredging has become a hot spot today, and the diffusion of overflow slurry is one of the sources of pollution generated by dredging suction dredgers. Therefore, combining with actual engineering conditions, this paper adopts the theory of computational fluid dynamics (CFD) to study the diffusion characteristics, diffusion range, and influencing factors and proposes construction strategies to reduce its pollution impact.

Application Research of Computational Fluid Mechanics Based on CNKI Database

Based on the China Knowledge Network Database (CNKI), a literature measurement analysis of the domestic computational fluid dynamics (CFD) application research was conducted. The results show that from 1973 to 2019, the number of articles published by CFD research has increased significantly year by year. The earliest literature on CFD published in the database was published in 1973, and more than 10 articles have been published annually since 2005. The text-issuing institutions are mainly well-known universities in China, among which Tianjin University has the most. Many masters and doctors in this university obtain degrees through researches related to computational fluid mechanics. CFD theory and software are mainly studied in Engineering technology and basic and applied basic research, and more research has been supported by the National Natural Science Foundation.

Numerical and Experimental Research on the Anti-sloshing Characteristic of Swash Bulkhead in LNG Independent Type C Tank

The sloshing induced by partial loaded in LNG (Liquified Natural Gas) independent type C tank will threat the structure of tank. For sloshing suppression, installation of swash bulkhead is a good choice. With model experiment, the sloshing suppression mechanism of perforated swash bulkhead is investigated. Comparing to the tank without swash bulkhead, the suppression efficiency is obtained. Base on the CFD (Computational fluid dynamic) theory, a numerical method is used to sloshing simulation of tank with perforated swash bulkhead, which is verified by the model experiment. Thus, with the same permeation ratio, the effect of anti-sloshing is analysed numerically with comparison of ring baffle and perforated bulkhead. It is found that perforated swash bulkhead has a better performance in sloshing suppression at higher filling level than the ring baffle. And there is a small variation in anti-sloshing efficiency of perforated swash bulkhead

Multiscale Eulerian CFD of Chemical Processes: A Review

This review covers the scope of multiscale computational fluid dynamics (CFD), laying the framework for studying hydrodynamics with and without chemical reactions in single and multiple phases regarded as continuum fluids. The molecular, coarse-grained particle, and meso-scale dynamics at the individual scale are excluded in this review. Scoping single-scale Eulerian CFD approaches, the necessity of multiscale CFD is highlighted. First, the Eulerian CFD theory, including the governing and turbulence equations, is described for single and multiple phases. The Reynolds-averaged Navier–Stokes (RANS)-based turbulence model such as the standard k-ε equation is briefly presented, which is commonly used for industrial flow conditions. Following the general CFD theories based on the first-principle laws, a multiscale CFD strategy interacting between micro- and macroscale domains is introduced. Next, the applications of single-scale CFD are presented for chemical and biological processes such as gas distributors, combustors, gas storage tanks, bioreactors, fuel cells, random- and structured-packing columns, gas-liquid bubble columns, and gas-solid and gas-liquid-solid fluidized beds. Several multiscale simulations coupled with Eulerian CFD are reported, focusing on the coupling strategy between two scales. Finally, challenges to multiscale CFD simulations are discussed. The need for experimental validation of CFD results is also presented to lay the groundwork for digital twins supported by CFD. This review culminates in conclusions and perspectives of multiscale CFD.

Numerical investigation of tsunami wave impacts on different coastal bridge decks using immersed boundary method

Due to the strong interaction between the bridges and the extreme waves generated by hurricanes and tsunamis, many coastal bridges were damaged in the past few decades. In this study, in order to investigate the effect of the extreme wave on a bridge, tsunami-like wave generated based on record in the Iwate station during 2011 Japan tsunami event instead of solitary wave is employed to impinge on the bridge with or without air vent. According to the Computational Fluid Dynamics (CFD) theory with a Volume of Fluid (VOF) interface tracking approach, a Numerical Wave Tank (NWT) is developed, in which the Immersed Boundary (IB) method is referred to simulate fluid and structure interaction. The model is calibrated with the experiment. In this numerical tank, the effects of tsunami-like waves with different prominent conditions including wave height and submersion depth on the bridges are studied. Besides, the efficiency of air vent in reducing the hydrodynamic load is also discussed. The results indicate that when the tsunami-like wave overtops the bridges, a noticeable overtopping, where the flow injects into the water fiercely and the whole flow field is very chaotic, is observed. The vertical forces on the bridges are larger than the horizontal forces, leading to many decks to collapse between two piers with small lateral displacement after the hurricanes and tsunamis. After the tsunami-like wave passes over the bridge, the oscillation of the residual wave causes the load oscillation of the bridge. The position of the bridge relative to the initial sea level has a serious impact on the forces on the bridge when the tsunami-like wave passes through it. With the increase of the wave height, the interaction intensity between the tsunami-like wave and the bridge is enhanced and the forces on the bridge also increase, but the effect duration reduces. After the air vent is installed, air vent can reduce the forces on the bridge and improve the efficiency of the bridge protection.

Offshore Wind Turbine Coupled Motion in Regular Waves

AbstractThis study aims to accurately predict the hydrodynamic performance and motion responses of offshore wind turbines on the basis of computational fluid dynamics (CFD) theory. Continuous and Navier-Stokes (N-S) equations are employed as control equations, and the k-ε model is used as a turbulence model. The finite difference method is utilized to discretize the equation. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm is applied to solve the control equation, and the volume-of-fluid (VOF) method is used to capture the free surface. The numerical wave tank of irregular wave is also established. The hydrodynamic performances and motion responses of the offshore wind turbines under regular waves are studied. First, we assume a floating foundation without the influence of a rotational fan and examine its motion responses and wave force in three typical sea conditions, namely, Levels 5, 6, and 7. Thereafter, we use a series of force and torque acting on the rotating center of the offshore to substitute for the influence of the rotational fan on the floating foundation. Then, we study the hydrodynamic performance influenced by blade rotation of the floating foundation in various sea conditions and three wind speeds, namely, 5, 8, and 11 m/s. Research results can provide usable theoretical principle and technical support for the investigation of the hydrodynamic performance and motion responses of similar offshore wind turbines.

Investigation on the lignite pyrolysis reaction kinetics based on the general Arrhenius formula

Studying the reaction kinetics can deepen the understanding of reaction mechanism and provide a relatively accurate and efficient reaction rate expression to theoretically optimize the relevant reactor. Here, the complicated lignite pyrolysis was assumed to be performed by the multi-parallel first order reactions, and the kinetic parameters of Arrhenius formula for each first order reaction were obtained through fitting the thermogravimetry (TG) experimental data. Thus, our developed kinetics models can avoid the multiple integration of using the well-known distributed activation energy model (DAEM) in evaluating the pyrolysis rate, the computational time for predicting the pyrolysis in a single lignite particle is reduced from 51.9 s to 3.8 s, which is important for theoretically optimizing the reactor, especially for using the well-developed computational fluid dynamics (CFD) theory. And, the simulating results showed that the developed kinetics model can more accurately predict the lignite pyrolysis process than that of DAEM.

Three Dimensional Study of Eddy Current Field and Temperature Field of 126kV three-phase enclosure-type GIS Bus

Heat is one of the most obvious characteristics of gas insulated switchgear (GIS) bus. This paper established three-dimensional eddy current field mathematical model for 126kV three-phase enclosure-type GIS bus. Magnetic field finite element method (FEM) was employed to calculate power loss in the conductors and the tank, and the result was the input data for the solution of temperature field. According to the theory of computational fluid dynamics (CFD),SF6 gas movement differential equations was given as well as solved region and boundary conditions of three dimensional fluid field. Nussle number was utilized to figure out nature convection coefficients of different segments of the bus. Solving the differential equations, fluid and temperature field distribution of the bus was calculated, which theoretically supported temperature on-line monitoring system of GIS bus.

Efficient Nonlinear Hydrodynamic Models for Wave Energy Converter Design—A Scoping Study

This review focuses on the most suitable form of hydrodynamic modeling for the next generation wave energy converter (WEC) design tools. To design and optimize a WEC, it is estimated that several million hours of operation must be simulated, perhaps one million hours of WEC simulation per year of the R&D program. This level of coverage is possible with linear potential flow (LPF) models, but the fidelity of the physics included is not adequate. Conversely, while Reynolds averaged Navier–Stokes (RANS) type computational fluid dynamics (CFD) solvers provide a high fidelity representation of the physics, the increased computational burden of these models renders the required amount of simulations infeasible. To scope the fast, high fidelity options, the present literature review aims to focus on what CFD theories exist intermediate to LPF and RANS as well as other modeling options that are computationally fast while retaining higher fidelity than LPF.

Study on numerical simulation of gas pipeline speed regulating detector

In order to control the running speed of the detector in the gas pipeline, the flow field calculation method of the detector in the gas pipeline under the discharge state is studied. Based on the operating principle of the detector in the gas pipeline, the model of the discharge hole of the detector is constructed by using the standard orifice flowmeter. Based on computational fluid dynamics theory, the application of computational fluid dynamics software ICEM CFD and provided ANSYS CFX to generate flow field model and a numerical simulation was carried out, with fluid flowing through the discharge of the flow field simulation, the discharge state of gas pipeline detector in flow field, achieved under different aperture of gas flowing through the standard orifice plate before and after the pressure field, velocity field of numerical analysis. The results show that using the standard hole as the detector model in the gas pipeline under the discharge state has certain guidance, and it is of certain significance to further study the velocity control problem of the detector in the gas pipeline.

Hydrodynamic performance of a floating breakwater as an oscillating-buoy type wave energy converter

Combined floating breakwater and wave energy converter systems have the potential to provide a cost-effective solution to offshore power supply and coastal protection. This will make wave energy economically competitive and commercial-scale wave power operations possible. This paper investigates the hydrodynamic features of wave energy converters that meet the dual objectives of wave energy extraction and attenuation for such a combined system. A two-dimensional numerical model was established using Star-CCM+ commercial software based on viscous Computational Fluid Dynamics theory to investigate the hydrodynamic performance of an oscillating buoy Wave Energy Converter (WEC) type floating breakwater under regular waves. The model proposed in this paper was verified with published experimental results. The hydrodynamics of symmetric and asymmetric floaters were investigated to demonstrate their wave attenuation and energy extraction performance, including square bottomed, triangular bottomed (with and without a baffle plate), and the Berkley Wedge. The asymmetric floaters were found to have higher power conversion efficiency and better wave attenuation performance, especially the Berkeley Wedge bottom device and the triangular-baffle bottom device. The triangular-baffle bottom device with a simpler geometry achieved similar wave attenuation and energy extraction performance characteristics to that of the Berkeley Wedge device. The maximum energy conversion efficiency of the triangular-baffle bottom floater reached up to 93%, an impressive WEC device among many designs for wave energy conversion. There may be a great potential for this newly proposed triangular-baffle bottom WEC type of floater to be an ideal coastal structure for both coastal protection and wave energy extraction.

Synectics model applied in basic theory of computational fluid dynamics

Computational fluid dynamics is taught in many universities and is a trending elective option among engineering students. Although analyzing computational fluid dynamics simulations is exciting enough, the theory is equation intensive, sometimes very abstract and also difficult to visualize for the novice. A creative thinking based approach termed synectics, which involves analogies, was therefore applied in classroom teaching to increase student comfort with the equations. For this purpose six analogies encompassing basic computational fluid dynamics concepts were developed along with pictorial representations, and are presented in this work. These analogies were integrated into classroom teaching via synectics procedures. Student feedback was positive and reflected higher engagement with the course compared to when the metaphoric activity was not implemented. This work attempts to demonstrate the feasibility and value of applying creative techniques, even when teaching a highly structured and equation oriented course such as computational fluid dynamics.

Numerical study on the effect of rocket plume to the jet flow deflector in liquid rocket engine test stage

Jet flow deflector is one of the most important facility in liquid rocket engine test stage. It is necessary to investigate the effect of rocket plume to the jet flow deflector. Based on the theory of computational fluid dynamics, the flow field of a rocket engine plume is simulated and analysed by numerical method. The velocity field and temperature field of the plume in rocket engine test are obtained. The structural characteristics of engine plume flow field and the impact effect on flow deflector are analysed. Finally, results are applied to the thermal protection design of the test stage.

Simulation and Research of CFD on Internal Pressure Parallel Hollow Fiber Membrane Module

Membrane bioreactor (MBR) has been widely used in sewage treatment, effectively solving many long-standing problems such as solid-liquid separation. In this paper, the internal pressure parallel type hollow fiber membrane module was taken as the research object. Based on the CFD theory and method, the solid-liquid separation of the flow entering the membrane module was simulated by FLUENT software. Firstly, the geometric model of the internal pressure parallel membrane module was established by the computational fluid dynamics (CFD) preprocessor and structured meshing was performed. Then the volume fraction of suspended solid (SS) at the exit of the model was calculated by Eulerian multi-phase flow model and Phase Coupled SIMPLE algorithm. The calculation results were presented as images in the CFD post processor. In this paper, the simulation calculation for different concentrations of suspended solid showed that the volume fraction of suspended solid at the exit of the model was zero, which was consistent with the actual MBR system operating data. The simulation results indicated that the model established in this paper had higher accuracy. The model can simulate and predict the separation effect of solid-liquid two-phase flow in wastewater treatment, which has certain reference value for MBR engineering design and research.