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.

Time-Domain Analysis of Body Freedom Flutter Based on 6DOF Equation

The reduced weight and improved efficiency of modern aeronautical structures result in a decreasing separation of frequency ranges of rigid and elastic modes.Particularly,a high-aspect-ratio flexible flying wing is prone to body freedomflutter(BFF),which is a result of coupling of the rigid body short-periodmodewith 1st wing bendingmode.Accurate prediction of the BFF characteristics is helpful to reflect the attitude changes of the vehicle intuitively and design the active flutter suppression control law.Instead of using the rigid body mode,this work simulates the rigid bodymotion of the model by using the six-degree-of-freedom(6DOF)equation.A dynamicmesh generation strategy particularly suitable for BFF simulation of free flying aircraft is developed.An accurate Computational Fluid Dynamics/Computational Structural Dynamics/six-degree-of-freedom equation(CFD/CSD/6DOF)-based BFF prediction method is proposed.Firstly,the time-domain CFD/CSD method is used to calculate the static equilibrium state of the model.Based on this state,the CFD/CSD/6DOF equation is solved in time domain to evaluate the structural response of themodel.Then combinedwith the variable stiffnessmethod,the critical flutter point of the model is obtained.This method is applied to the BFF calculation of a flyingwing model.The calculation results of the BFF characteristics of the model agree well with those fromthe modalmethod andNastran software.Finally,the method is used to analyze the influence factors of BFF.The analysis results show that the flutter speed can be improved by either releasing plunge constraint or moving the center ofmass forward or increasing the pitch inertia.

Analysis and Research on Aerodynamic Characteristics of Quad Tilt Rotor Aircraft

For the quad tilt rotor aircraft, a computational fluid dynamics method based on multiple reference frames (MRF) was used to analyze the influence of aerodynamic layout parameters on the aerodynamic characteristics of the quad tilt rotor aircraft. Firstly, a numerical simulation method for the interference flow field of the quad tilt rotor aircraft is established. Based on this method, the aerodynamic characteristics of isolated rotors, rotor combinations at different lateral positions on the wing, and rotor rotation directions under different inflow velocities were calculated and analyzed, in order to grasp their aerodynamic interference laws and provide reference for the design and control theory research of such aircraft.

Inertisation options for BG method and optimisation using CFD modelling

Spontaneous combustion(sponcom) is one of the issues of concern with the blasting gallery(BG) method of coal mining and has the potential to cause fires, and impact on production and safety, greenhouse gas(GHG) emissions and huge costs involved in controlling the aftermath situations. Some of the research attempts made to prevent and control coal mine fires and spontaneous combustion in thick seams worked with bord and pillar mining methods are presented in this paper. In the study, computational fluid dynamics(CFD) modelling techniques were used to simulate and assess the effects of various mining methods, layouts, designs, and different operational and ventilation parameters on the flow of goaf gases in BG panels. A wide range of parametric studies were conducted to develop proactive strategies to control and prevent ingress of oxygen into the goaf area preventing spontaneous combustion and mine fires.

Analysis of Wave Added Drag and Motion Response of Mid-high-speed Ship against Waves

In order to accurately predict the on-wave resistance and responses to hull motions of ships in actual sea conditions,the k-εmethod of the RNG model is adopted on the basis of the unsteady RANS method.The two-formula turbulence model deals with the viscous flow,the VOF method captures the free surface,the velocity boundary method makes waves,the artificial damping method is used to eliminate waves,and the nested grid technology is used to deal with the motion response of ships on waves.Combined with the 6-DOF motion formula,a three-dimensional numerical wave cell for regular waves is established.For one example,taking a KCS Container ship and fishing boat sailing at a mid-high-speed,the increase of wave resistance and motion response at different wavelengths are analyzed,and the simulation results are compared with the experimental value,the content of strip theory in potential flow theory and the panel method to prove the reliability of CFD method in predicting ship motion.

Experimental and Numerical Investigations of Ship Parametric Rolling in Regular Head Waves

Parametric rolling is one of five types of the ship stability failure modes as proposed by IMO. The periodic change of the metacentric height is often considered as the internal cause of this phenomenon. Parametric rolling is a complex nonlinear hydrodynamic problem, often accompanied by large amplitude vertical motions of ships. In recent years,the Reynolds-averaged Navier–Stokes(RANS) equation simulations for viscous flows have made great progress in the field of ship seakeeping. In this paper, the parametric rolling for the C11 containership in regular waves is studied both experimentally and numerically. In the experiments, parametric rolling amplitudes at different drafts, forward speeds and wave steepnesses are analyzed. The differences in the steady amplitudes of parametric rolling are observed for two drafts. The effect of the incident wave steepness(or wave amplitude) is also studied, and this supports previous results obtained on limits of the stability for parametric rolling. In numerical simulations, the ship motions of parametric rolling are analyzed by use of the potential-flow and viscous-flow methods. In the viscousflow method, the Reynolds-averaged Navier–Stokes equations are solved using the overset grid method. The numerical accuracies of the two methods at different wave steepnesses are also discussed.

On the Effect of the Rotating Chamber Reverse Speed on the Mixing of SiC Ceramic Particles in a Dry Granulation Process

In order to control the accumulation of SiC ceramic particles on the wall of the rotating chamber in the frame of a dry granulation process,the effect of the wall reverse speed on the mixing process is investigated.In particular,an Euler-Euler two-phase flow model is used to analyze the dynamics of both SiC particles and air.The numerical results show that by setting a certain reverse rotating speed of the rotating chamber,the accumulation of SiC particles on the wall can be improved,i.e.,their direction of motion in proximity to the wall can be changed and particles can be forced to re-join the granulation process.Experimental tests conducted to verify the reliability of the numerical findings,demonstrate that when the reverse rotating speed of the rotating chamber is 4 r/min,the sphericity of SiC particles in the rotating chamber is the highest and the fluidity is the best possible one.

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.

Dynamic Analysis of Single Pile in Liquefied Soils Considered as Newtonian Fluid

Case histories have shown that the liquefaction-induced soil lateral spreading is one of the main causes of damage to pile foundations subjected to seismic loading. Post-liquefaction soil behaves similarly to a viscous fluid. This study investigated the effect of soil lateral spreading on a single pile based on fluid mechanics in which the liquefied soils were treated as Newtonian fluids. A numerical simulation on a single pile embedded in a fully saturated sandy foundation was conducted and compared with shake table tests. The lateral flow effect and the effect of shear strain rate were discussed. After liquefaction, the acceleration of the foundation shows that there are no obvious spikes and finally reaches a stable state. The presented method can predict the pile response better than p-y curve method. A parametric study was performed to explore the effect of several influence factors on pile behaviors. The results show that the pile head displacement decreases and the maximum bending moment at pile bottom increases with the increase of bending stiffness. With the same pile bending stiffness, the displacement and bending moment of pile increase with the increase of soil viscosity and acceleration amplitude.

Semi-submersible Offshore Coupled Motion in Irregular Waves

In order to predict the hydrodynamic performance of semi-submersible offshore platform accurately,based on CFD theory,continuous equation and N-S equation as the control equation,RNG type k-εmodel as turbulence model,using the finite difference method to discretize the control equation,using the Semi-Implicit Method for Pressure Linked Equation(SIMPLE)algorithm to solve the control equation,using the VOF method to capture the free surface.The numerical wave tank of irregular wave is established,and the wave force and motion response of the semi-submersible platform under irregular wave are studied.Based on the Jonswap spectrum density function,for a certain area of two irregular waves(South China sea,a-ten-year return period,a-hundred-year return period)sea condition,five wave direction Angle(0°,30°,45°,60°,90°),a total of 10 kinds of conditions of the motion response of semi-submersible platform are simulated,through analysis and comparison of simulation results,the influence law of wave angle,wave period and wave height on platform motion is obtained.Compared with the experimental values,the results of heave and pitch are close to the experimental data under the sea condition of 2,0 degree wave angles.The research results in this paper can provide reference for the design and motion response prediction of practical semi-submersible offshore platforms.

A New Single-blade Based Hybrid CFD Method for Hovering and Forward-flight Rotor Computation

A hybrid Euler/full potential/Lagrangian wake method,based on single-blade simulation,for predicting unsteady aerodynamic flow around helicopter rotors in hover and forward flight has been developed.In this method,an Euler solver is used to model the near wake evolution and transonic flow phenomena in the vicinity of the blade,and a full potential equation（FPE） is used to model the isentropic potential flow region far away from the rotor,while the wake effects of other blades and the far wake are incorporated into the flow solution as an induced inflow distribution using a Lagrangian based wake analysis.To further reduce the execution time,the computational fluid dynamics（CFD） solution and rotor wake analysis（including induced velocity up-date） are conducted parallelly,and a load balancing strategy is employed to account for the information exchange between two solvers.By the developed method,several hover and forward-flight cases on Caradonna-Tung and Helishape 7A rotors are per-formed.Good agreements of the loadings on blade surface with available measured data demonstrate the validation of the method.Also,the CPU time required for different computation runs is compared in the paper,and the results show that the pre-sent hybrid method is superior to conventional CFD method in time cost,and will be more efficient with the number of blades increasing.

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.

Novel oxygen-enrichment method using annular air curtain for single-head roadway of plateau mine

The low-oxygen environment restricts the exploitation of mineral resources on plateaus and affects miner’s safety.This paper proposes an oxygen-enrichment method using an annular air curtain.Through numerical simulation and experiments,it was confirmed that the proposed method improves the breathing environment in the single-head roadway of a plateau mine.Computational fluid dynamics(CFD)was used to investigate the oxygen-enriching effect and oxygen spatial distribution regularities after using the proposed oxygen-enrichment method in the single-head roadway of a plateau mine.The reliability of the CFD model was confirmed by experiment.Orthogonal testing was conducted to investigate the influence degree and optimal level combination of factors influencing oxygen enrichment.The results demonstrate that the annular air curtain effectively prevented oxygen loss,thus forming a local oxygen-rich space and improving the effective utilization rate of oxygen.Oxygen supply concentration and velocity are positively correlated with the oronasal oxygen mass fraction through a linear function,while the air curtain outlet wind velocity is negatively correlated with the oronasal oxygen mass fraction through a linear function.The annular air curtain diameter and oronasal oxygen mass fraction do not have an obvious functional relationship.When the annular air curtain diameter was greater than 0.9 m,the oronasal oxygen mass fraction was stable at approximately 25.30%.The influencing factors of the novel oxygen-enrichment method are,in descending order,as follows:oxygen supply concentration,annular air curtain diameter,air curtain outlet wind velocity,and oxygen supply velocity.The optimal level combination is oxygen supply concentration of 100%,oxygen supply velocity of 11 m/s,air curtain outlet wind velocity of 1.5 m/s,and annular air curtain diameter of 0.9 m.

Inverse design of mesoscopic models for compressible flow using the Chapman-Enskog analysis

In this paper,based on simplified Boltzmann equation,we explore the inverse-design of mesoscopic models for compressible flow using the Chapman-Enskog analysis.Starting from the single-relaxation-time Boltzmann equation with an additional source term,two model Boltzmann equations for two reduced distribution functions are obtained,each then also having an additional undetermined source term.Under this general framework and using Navier-Stokes-Fourier(NSF)equations as constraints,the structures of the distribution functions are obtained by the leading-order Chapman-Enskog analysis.Next,five basic constraints for the design of the two source terms are obtained in order to recover the NSF system in the continuum limit.These constraints allow for adjustable bulk-to-shear viscosity ratio,Prandtl number as well as a thermal energy source.The specific forms of the two source terms can be determined through proper physical considerations and numerical implementation requirements.By employing the truncated Hermite expansion,one design for the two source terms is proposed.Moreover,three well-known mesoscopic models in the literature are shown to be compatible with these five constraints.In addition,the consistent implementation of boundary conditions is also explored by using the Chapman-Enskog expansion at the NSF order.Finally,based on the higher-order Chapman-Enskog expansion of the distribution functions,we derive the complete analytical expressions for the viscous stress tensor and the heat flux.Some underlying physics can be further explored using the DNS simulation data based on the proposed model.

A novel point source oxygen supply method for sleeping environment improvement at high altitudes

The hypoxic environment at high altitudes causes various sleep disorders.Diffuse oxygen enrichment is an effective way to alleviate sleep disorders and improve the built environment in high altitude areas.In this study,a novel point source local diffuse oxygen supply method was proposed to improve the sleeping oxygen environment.The oxygen supply performance was investigated by the computational fluid dynamics(CFD)method including the oxygen concentration and air velocity distributions.A sleeping experiment was conducted on the plateau to validate the CFD model.The occupied zone including the inhalation zone and the active zone was defined.The results showed that the oxygen concentration showed a rapid rise,then decreased slowly,and finally tended to be stable.The oxygen concentration after stabilization was remarkably influenced by indoor ventilation rate.The sleeping environment’s improvement was examined considering the oxygen enrichment efficiency,uniformity,stability and human comfort demand.The optimal strategies were recommended with a ventilation rate of 1 air change per hour,supplied oxygen concentration of 90%;and jet distance of 0.50 m.The study contributes to improving the oxygen environment and human sleep quality in an effective and energy-saving approach to the sustainable development of buildings in high altitude areas.

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.

Numerical Investigation into the Distributor Design in Radial Flow Adsorber

Air flow distribution in radial flow adsorber was numerically investigated using computational fluid dynamics(CFD)method,which was proved to be applicable to study the problem of non-uniform distribution in radial flow adsorber.Results showed that the degree of non-uniformity was more serious in desorption process than that is adsorption process.Therefore,it was considered that the non-uniform distribution of flow in a radial flow adsorber was mainly manifested in the desorption process.Optimum design of distributor parameters can improve the flow distribution in adsorber.Meanwhile,three different structures of distributor and the effect of breathing valve were analyzed.Results revealed that truncated cone is more effective than tubular and conical distributors in flow distribution.By inserting the truncated cone in central channel,desorption uniformity was increased by 6.56%and the breakthrough time of CO_(2)was extended from 564s to 1138s in the adsorption process.The“dead zone”problem at the top of adsorber during the desorption process was solved by opening breathing valve,which prolonged the working life of adsorber and was proved to have less effect on the uniform of airflow.

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.

Adaptive Optimal Control of the Flapping Rule of a Fixed Flapping Plate

In this paper,with the use of the moving boundary computational fluid dynamics method,we developed a new real-time optimal control method which can be used to find the optimal flapping mode of a fixed flapping plate.The results show that there is a 54.0%increase in the thrust obtained by the unsteady optimal flapping rule.In addition,to reduce the cost of computation and to have a better understanding of the flapping rule,the maximum velocity at the end tip of the flapping plate is taken as the objective functional,with which the thrust is increased by 22.9%.

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.