Numerical Study on the Aerodynamic and Fluid−Structure Interaction of An NREL-5MW Wind Turbine

A 5-MW wind turbine has been modeled and analyzed for fluid-structure interaction and aerodynamic performance.In this study, a full-scale model of a 5-MW wind turbine is first developed based on a computational fluid dynamics(CFD) approach, in which the unsteady, noncompressible Reynolds Averaged Navier-Stokes(RANS) method is used. The main focus of the study is to analyze the tower shadow effect on the aerodynamic performance of the wind turbine under different inlet flow conditions. Subsequently, the finite element model is established by considering fluid/structure interactions to study the structural stress, displacement, strain distributions and flow field information of the structure under the uniform wind speed. Finally, the fluid-structure interaction model is established by considering turbulent wind and the tower shadow effect. The variation rules of the dynamic response of the one-way and two-way fluid-structure interaction(FSI) models under different wind speeds are analyzed, and the numerical calculation results are compared with those of the centralized mass model. The results show that the tower shadow effect and structural deformation are the main factors affecting the aerodynamic load fluctuation of the wind turbine, which in turn affects the aerodynamic performance and structural stability of the blades. The structural dynamic response of the coupled model shows significant similarity, while the structural displacement response of the former exhibits less fluctuation compared with the conventional centralized mass model. The one-way fluid-structure interaction(FSI)model shows a higher frequency of stress-strain and displacement oscillations on the blade compared with the two-way FSI model.

Review:Recent Development of High⁃Order⁃Spectral Method Combined with Computational Fluid Dynamics Method for Wave⁃Structure Interactions

The present paper reviews the recent developments of a high⁃order⁃spectral method(HOS)and the combination with computational fluid dynamics(CFD)method for wave⁃structure interactions.As the numerical simulations of wave⁃structure interaction require efficiency and accuracy,as well as the ability in calculating in open sea states,the HOS method has its strength in both generating extreme waves in open seas and fast convergence in simulations,while computational fluid dynamics(CFD)method has its advantages in simulating violent wave⁃structure interactions.This paper provides the new thoughts for fast and accurate simulations,as well as the future work on innovations in fine fluid field of numerical simulations.

Numerical Study on Effects of Door-Opening on Airflow Patterns and Dynamic Cross-Contamination in an ISO Class 5 Operating Room

The contamination diffusion to the operating room when the door is open was simulated with a computational fluid dynamic(CFD) method,to give the extent of the contamination diffusion.The influence of the door-opening procedure was ignored since the door of the operating room is normally a sliding one.The flow field in the case of the 16 s course of opening the door was simulated.The simulated and the experimental results demonstrate that the extent of the contamination diffusion is around 1.5 m when there is no temperature difference between indoor and outdoor,and there is hardly any contamination diffusion when the temperature difference is 1 ℃.It can be concluded that the positive pressure difference in the operating room lost its function in preventing the contamination when the door is open.That the temperature of corridor is lower than that of operating room contributes to contamination control.Keeping 1 ℃ temperature difference between corridor and operating room and increasing positive pressure and air flow are suggested.It is more secure to set up an anteroom if persons come in or out of the operation room at the course of surgery.

Analysis of gas-solid flow and shaft-injected gas distribution in an oxygen blast furnace using a discrete element method and computational fluid dynamics coupled model

lronmaking using an oxygen blast furnace is an attractive approach for reducing energy consumption in the iron and steel industry. This paper presents a numerical study of gas-solid flow in an oxygen blast fur- nace by coupling the discrete element method with computational fluid dynamics. The model reliability was verified by previous experimental results. The influences of particle diameter, shaft tuyere size, and specific ratio （X） of shaft-injected gas （51G） flowrate to total gas flowrate on the SIC penetration behavior and pressure field in the furnace were investigated. The results showed that gas penetration capacity in the furnace gradually decreased as the particle diameter decreased from 100 to 40 mm. Decreasing particle diameter and increasing shaft tuyere size both slightly increased the SIG concentration near the furnace wall but decreased it at the furnace center. The value of X has a significant impact on the SIG distribution. According to the pressure fields obtained under different conditions, the key factor affecting SIG penetration depth is the pressure difference between the upper and lower levels of the shaft tuyere. If the pressure difference is small, the SIG can easily penetrate to the furnace center.

Computational Fluid Dynamics Uncertainty Analysis for Simulations of Roll Motions for a 3D Ship

The roll motions are influenced by significant viscous effects such as the flow separation.The 3D simulations of free decay roll motions for the ship model DTMB 5512 are carried out by Reynold averaged NavierStokes(RANS) method based on the dynamic mesh technique.A new moving mesh technique is adopted and discussed in details for the present simulations.The purpose of the research is to obtain accurate numerical prediction for roll motions with their respective numerical/modeling errors and uncertainties.Errors and uncertainties are estimated by performing the modern verification and validation(V&V) procedures.Simulation results for the free-floating surface combatant are used to calculate the linear,nonlinear damping coefficients and resonant frequencies including a wide range of forward speed.The present work can provide a useful reference to calculate roll damping by computational fluid dynamics(CFD) method and simulate a general ship motions in waves.

Combustion characteristics of low-quality lignite for different bed material sphericities in a circulating fluidized bed boiler:A numerical study

This study delves into the combustion behavior of various lignite types within a circulating fluidized bed boiler(CFBB),with a primary focus on the impact of different bed material sphericity ratios(0.5,0.7,and 0.9).Utilizing bed material with a sphericity ratio of 0.9 sourced from theÇan power plant and verified through experimentation,the research reveals several key findings.Notably,furnace temperatures tended to rise with higher sphericity ratios,albeit with variations between lignite types,particularly highlighting the complexity of this relationship in the case of GLI-Tunçbilek lignite.Pressure levels in the combustion chamber remained consistent across different sphericity ratios,indicating minimal influence on pressure dynamics.Improved combustion efficiency,especially at the bottom of the boiler,was observed at lower sphericity levels(0.5 and 0.7)forÇan lignite,as reflected in CO_(2) mole fractions.While NO_(x) emissions generally decreased with lower sphericity,the sensitivity to sphericity varied by lignite type,with Ilgın lignite showcasing low NO_(x) but high SO_(2) emissions,underscoring the intricate interplay between lignite properties,sphericity,and emissions.Overall,this study advances our understanding of CFBB combustion dynamics,offering insights valuable for optimizing performance and emissions control,particularly in lignite-based power.

Numerical simulation on melt flow with bubble stirring and temperature field in aluminum holding furnace

The numerical model for predicting the flow and temperature fields of the melt in holding furnace with porous brick purging system were set up using Euler-Lagrange approach.In this model,bubbles coalescence and disintegration were ignored based on the dimensionless analysis,and the bubble size was assumed to be obedient to Rosin-Rammler distribution with a mean size of 0.6 mm.The results show that on reference operating condition,during the heating and agitation process,melt mixes well in the furnace,and the melt velocity increases with the increase of gas flux.Holding the melt for 30 min causes the max temperature in the bulk melt to increase to 60 K.After holding the heat,the agitation processing restarts,and it takes 10 min for the stratified melt to retrieve the homogeneous temperature field when the gas flux is 10 L/min,which shows deficient alloying and degassing in the melt.With the increase of gas flux from 10 to 20,30 and 40 L/min,the necessary recovery time decreases from 10 to 6,5 and 4 min gradually,which shows the improvement of the stirring efficiency.Depending on the processing purposes,for both good degassing performance and gas saving,proper operating strategy and parameters (gas flux,primarily) could be adjusted.

A combined multiscale modeling and experimental study on surface modification of high-volume micro-nanoparticles with atomic accuracy

Surface modification for micro-nanoparticles at the atomic and close-to-atomic scales is of great importance to enhance their performance in various applications,including high-volume battery,persistent luminescence,etc.Fluidized bed atomic layer deposition(FB-ALD)is a promising atomic-scale manufacturing technology that offers ultrathin films on large amounts of particulate materials.Nevertheless,nanoparticles tend to agglomerate due to the strong cohesive forces,which is much unfavorable to the film conformality and also hinders their real applications.In this paper,the particle fluidization process in an ultrasonic vibration-assisted FB-ALD reactor is numerically investigated from micro-scale to macro-scale through the multiscale computational fluid dynamics and discrete element method(CFD-DEM)modeling with experimental verification.Various vibration amplitudes and frequencies are investigated in terms of their effects on the fluid dynamics,distribution of particle velocity and solid volume fraction,as well as the size of agglomerates.Results show that the fluid turbulent kinetic energy,which is the key power source for the particles to obtain the kinetic energy for overcoming the interparticle agglomeration forces,can be strengthened obviously by the ultrasonic vibration.Besides,the application of ultrasonic vibration is found to reduce the mean agglomerate size in the FB.This is bound to facilitate the heat transfer and precursor diffusion in the entire FB-ALD reactor and the agglomerates,which can largely shorten the coating time and improve the film conformality as well as precursor utilization.The simulation results also agree well with our battery experimental results,verifying the validity of the multiscale CFD-DEM model.This work has provided momentous guidance to the mass manufacturing of atomic-scale particle coating from lab-scale to industrial applications.

CFD simulation of an industrial hydrocyclone with Eulerian-Eulerian approach: A case study

In the present study, a three-dimensional computational fluid dynamics simulation together with experimental field measurements was applied to optimize the performance of an industrial hydrocyclone at Sarcheshmeh copper complex. In the simulation, the Eulerian–Eulerian approach was used for solid and liquid phases, the latter being water. In this approach, nine continuous phases were considered for the solid particles with different sizes and one continuous phase for water. The continuity and momentum equations with inclusion of buoyancy and drag forces were solved by the finite volume method. The k–e RNG turbulence model was used for modeling of turbulency. There was a good agreement between the simulation results and the experimental data. After validation of the model accuracy, the effect of inlet solid percentage, pulp inlet velocity, rod inserting in the middle of the hydrocyclone and apex diameter on hydrocyclone performance was investigated. The results showed that by decreasing the inlet solid percentage and increasing the pulp inlet velocity, the efficiency of hydrocyclone increased. Decreasing the apex diameter caused an increase in the hydrocyclone efficiency.

Numerical modelling of flow and transport in rough fractures

Simulation of flow and transport through rough walled rock fractures is investigated using the latticeBoltzmann method （LBM） and random walk （RW）, respectively. The numerical implementation isdeveloped and validated on general purpose graphic processing units （GPGPUs）. Both the LBM and RWmethod are well suited to parallel implementation on GPGPUs because they require only next-neighbourcommunication and thus can reduce expenses. The LBM model is an order of magnitude faster onGPGPUs than published results for LBM simulations run on modern CPUs. The fluid model is verified forparallel plate flow, backward facing step and single fracture flow; and the RWmodel is verified for pointsourcediffusion, Taylor-Aris dispersion and breakthrough behaviour in a single fracture. Both algorithmsplace limitations on the discrete displacement of fluid or particle transport per time step to minimise thenumerical error that must be considered during implementation. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Investigation of particle-wall interaction in a pseudo-2D fluidized bed using CFD-DEM simulations

We report on discrete element method simulations of a pseudo-two-dimensional （pseudo-2D） fluidized bed to investigate particle-wall interactions. Detailed information on macroscopic flow field variables, including solids pressure, granular temperature, and normal and tangential wall stresses are analyzed. The normal wall stress differs from the solids pressure because of the strong anisotropic flow behavior in the pseudo-2D system. A simple linear relationship exists between normal wall stress and solids pressure. In addition, an effective friction coefficient can be derived to characterize particle-wall flow interaction after evaluating the normal and tangential wall stresses. The effects of inter-particle and particle-wall friction coefficients are evaluated. Strong anisotropic flow behavior in the pseudo-2D system needs to be considered to validate the two-fluid model where the boundary condition is usually developed based on an isotropic assumption. The conclusion has been confirmed by simulation with different particle stiffnesses. Assumptions in the newly developed model for 2D simulation are further examined against the discrete element method simulation.

Numerical study on transom stern ventilation and resistance of high-speed ship in calm water

A transom stern is a common design feature for a high-speed ship.In the present study,the transom stern ventilation of NPL 3b,5b hull is investigated by three methods:H−H formula,Doctors’formula,and computational fluid dynamics(CFD)method at first.For the CFD method,the ratios of the wave elevation and wetted area are used to determine the transom ventilation.Comparisons of results show that Doctors’formula is more accurate to calculate the critical transom draft Froude number.And then a Rankine panel method(RPM)based on the high-order boundary element method incorporated the modified transom stern condition is implemented to evaluate the steady wave problem of a high-speed fishery patrol ship in calm water.Besides,free-surface(FS)and double body(DB)simulations based on Star-CCM+are carried out to obtain the wave-making resistance and total resistance.The results of the resistance and wave pattern around the fishery patrol ship computed by RPM show generally good agreement with experimental measurement and CFD results.Numerical results indicate that the developed Rankine panel method with transom condition could predict the resistance of high-speed displacement ships with good accuracy.

Investigation into improving the efficiency and accuracy of CFD/DEM simulations

The Euler-Lagrange approach combined with a discrete element method has frequently been applied to elucidate the hydrodynamic behavior of dense fluid-solid flows in fluidized beds. In this work, the efficiency and accuracy of this model are investigated. Parameter studies are performed; in these studies, the stiffness coefficient, the fluid time step and the processor number are varied under conditions with different numbers of particles and different particle diameters. The obtained results are compared with measurements to derive the optimum parameters for CFD/DEM simulations. The results suggest that the application of higher stiffness coefficients slightly improves the simulation accuracy. However, the average computing time increases exponentially. At larger fluid time steps, the results show that the average computation time is independent of the applied fluid time step whereas the simulation accuracy decreases greatly with increasing the fluid time step. The use of smaller time steps leads to negligible improvements in the simulation accuracy but results in an exponential rise in the average computing time. The parallelization accelerates the DEM simulations if the critical number for the domain decomposition is not reached. Above this number, the performance is no longer proportional to the number of processors. The critical number for the domain decomposition depends on the number of particles. An increase in solid contents results in a shift of the critical decomposition number to higher numbers of CPUs.

A hybrid DEM/CFD approach for solid-liquid flows

A hybrid scheme coupling the discrete element method （DEM） with the computational fluid dynamics （CFD） is developed to model solid-liquid flows. Instead of solving the pressure Poisson equation, we use the compressible volume-averaged continuity and momentum equations with an isothermal stiff equation of state for the liquid phase in our CFD scheme. The motion of the solid phase is obtained by using the DEM, in which the particle-particle and particle-wall interactions are modelled by using the theoretical contact mechanics. The two phases are coupled through the Newton＇s third law of motion. To verify the proposed method, the sedi-mentation of a single spherical particle is simulated in water, and the results are compared with experimental results reported in the literature. In addition, the drafting, kissing, and tumbling （DKT） phenomenon between two particles in a liquid is modelled and rea-sonable results are obtained. Finally, the numerical simulation of the density-driven segregation of a binary particulate suspension in-volving 10 000 particles in a closed container is conducted to show that the presented method is potentially powerful to simulate real particulate flows with large number of moving particles.

Eulerian-Lagrangian simulation of distinct clustering phenomena and RTDs in riser and downer

Numerical simulation of fully developed hydrodynamics of a riser and a downer was carried out using an Eulerian-Lagrangian model, where the particles are modeled by the discrete element method （DEM） and the gas by the Navier-Stokes equations. Periodic flow domain with two side walls was adopted to simulate the fully developed dynamics in a 2D channel of 10 cm in width. All the simulations were carried out under the same superficial gas velocity and solids holdup in the domain, starting with a homogenous state for both gas and solids, and followed by the evolution of the dynamics to the heterogeneous state with distinct clustering in the riser and the downer. In the riser, particle clusters move slowly, tending to suspend along the wall or to flow downwards, which causes wide residence time distribution of the particles. In the downer, clusters still exist, but they have faster velocities than the discrete particles. Loosely collected particles in the clusters move in the same direction as the bulk flow, resulting in plug flow in the downer. The residence time distribution （RTD） of solids was computed by tracking the displacements of all particles in the flow direction. The results show a rather wide RTD for the solids in the riser hut a sharp peak RTD in the downer, much in agreement with the experimental findings in the literature. The ensemble average of transient dynamics also shows reasonable profiles of solids volume fraction and solids velocity, and their dependence on particle density.

Modeling and simulation of chemically reacting flows in gas-solid catalytic and non-catalytic processes

This paper gives an overview of the recent development of modeling and simulation of chemically react- ing flows in gas-solid catalytic and non-catalytic processes. General methodology has been focused on the Eulerian-Lagrangian description of particulate flows, where the particles behave as the catalysts or the reactant materials. For the strong interaction between the transport phenomena （i.e., momentum, heat and mass transfer） and the chemical reactions at the particle scale, a cross-scale modeling approach, i.e., CFD-DEM or CFD-DPM, is established for describing a wide variety of complex reacting flows in multiphase reactors, Representative processes, including fluid catalytic cracking （FCC）, catalytic conversion of syngas to methane, and coal pyrolysis to acetylene in thermal plasma, are chosen as case studies to demonstrate the unique advantages of the theoretical scheme based on the integrated particle-scale information with clear physical meanings, This type of modeling approach provides a solid basis for understanding the multiphase reacting flow problems in general.

Effect of geometric parameters at open turbine combined structure on flow field distribution of dry granulation for Si_(3)N_(4) powder

To improve the uniformity of the flow field and the poor axial velocity in the chamber of Si3N4 dry granulation, the influence of geometric parameters at open turbinecombined structure on the flow field distribution is studied. The Euler–Euler gas-solidtwo-phase flow model is established and the physical model of dry granulation chamberunder the combined structure is simplified. Under the same radial structure, the volumedistribution and velocity field of Si3N4 particles in the granulation chamber with a different number and angle of the axial structure at the open turbine are analyzed by theCFD method. The influence of the axial structure at the open turbine on the flow fielddistribution of Si3N4 particles under different geometric parameters is compared. Theresults show that the axial structure of the open turbine in the granulation chamber isthe most uniform when the number of blades is 6 and the inclination angle is 45◦, andthe circulating flow of the upper and lower parts of Si3N4 powder is strong.