In many industrial applications, gas-liquid-particle three-phase flows are observed. Predicting erosion damage in this type of flow is a challenging issue, and so many factors, such as the liquid film behavior have significant effects on the erosion rate. In the present study, the Eulerian-Lagrangian approach was implemented to study the process of sand particle erosion in elbows with different bend angles. For this purpose, gas and liquid phases under annular flow conditions were introduced at the pipe inlet, and the volume of fluid (VOF) method was employed to solve the governing equations. For evaluating the erosion rate, the Det Norske Veritas (DNV) model was applied. The predicted erosion results for the bend angles of 30°, 60° and 90° at different orientations were compared with those of the two-phase gas-particle flows. The simulation results indicated that for gas-liquid-particle flow, the behavior of film thickness in the bend plays a major role on the particle impact velocity and the corresponding erosion rates. By comparing the impact characteristics for gas and liquid superficial velocities of 40 and 0.4 m/s, respectively, in the 90° elbow, it was found that the impact velocities for gas-particle and gas-liquid-particle flows at the erosion hotspot are 38 and 14 m/s, respectively. In addition, among the studied geometries, the 30° elbow is the most erosion-resistant bend angle configuration among those studied for both two- and three-phase flows.

In this study, the Brownian diffusion of elongated nano-fibers was investigated numerically. Motions of nano-fibers of different sizes and aspect ratios were resolved by solving the corresponding system of equations governing their coupled translational and rotational motions. The study allowed a close examination of the Brownian diffusion of nano-fibers with respect to the coupling of their translational and rotational motions and how the rotation affects the fibrous particle macroscopic diffusion properties. Particular attention was given to the rotational relaxation time in determining the isotropic and anisotropic diffusive properties of elongated particles. Theoretical and semi-empirical equations were developed to quantify the diffusion coefficients of nano-fibers. Orientation averaged mobility of the nanofiber, nanorod and non-spherical nano-agglomerates was examined by the newly developed Brownian diffusion model. The result was compared with the particle mobility by collision limited reaction rate theory, empirical models and the experimental measurements. The study led to the discovery of a surface dominated mobility for nanoparticles with Knudsen number greater than 5 (Kn > 5). For particles in this range, all morphologies can be viewed as point collision and therefore the use of the equivalent surface mobility diameter was reasonably justified. Beyond this range when Kn < 0.1, however, the study showed that the particle morphology starts to play an important role, and accuracy of the surface mobility approximation reduces as the Knudsen number decreases. The study opened up new approaches for studying fundamental diffusive processes of nano-particles of complex shapes which are numerous in natural environment.

Fracking (fracturing) is of great importance for enhancing oil and gas production from low permeability reservoirs. Since in fracking fluid, suspension of sand particles are used, the erosion failure of fracturing equipment has become an increasing concern. Accordingly, investigation of erosion of commonly used fittings such as ball seats in order to decrease its adverse consequences has attracted considerable attentions. Although the erosion wear of gas-solid flows in the pipe sudden expansion was investigated in the literature, the effect of particle size, ball seat shape and the contraction configurations on the erosion-induced wear is not fully understood. This study is aimed to explore the most erosion-resistant configuration of a ball seat under various operational conditions. A CFD model is used and a wide range of geometries are investigated. The studied configurations are categorized in three main groups including single cone, double cone and curved cone. In each category, different cone angles and curve styles are considered. The results showed that, among the single cone ball seats, the cone angle of 15° is the most erosion-resistant configuration. It was also shown that the third-order curve style cone has the best erosion performance.

Sand particle erosion is the main cause of the failure of bends in the natural gas pipelines. The rapid progress of computational power and modern numerical methods has provided the opportunity for developing realistic simulation of the erosion process. The goal of this paper is to predict the sand erosion rates with the use of computational fluid dynamics in the gas/solid flows in the plugged tees and standard elbows. For this purpose, the Eulerian-Lagrangian approach was used. To simulate the flow, the SIMPLE algorithm and the k-ω SST turbulence model were used. Particles were injected into the inlet pipe with different sizes. To predict more realistic results the Grant and Tabakoff stochastic rebound model was applied and the Oka model was used to calculate erosion. The results showed that, the use of plugged tee instead of a standard elbow would reduce the erosion rate only for fine particles. Also, for them, by increasing the plugged length the pipe will experience less erosion. For coarser particles, however, the vortex created in the plugged section did not affect the particles velocity; therefore, the erosion rate was not reduced.

Particle dispersion and deposition in a modeled room was investigated using the Lattice Boltzmann method (LBM) in conjunction with the hybrid RANS/LES turbulence model. For this new model a combination of LES and RANS models was used to reduce the computational cost of using the full LES in the entire domain. Here the near wall region was simulated by the RANS model, while the rest of the domain was analyzed using the LES model within the framework of the LBM. The k-ε turbulence model was applied in the RANS region. For using the k-ε model in the LBM framework, two additional distribution functions for k and ε were defined. For the LES region the sub-grid scale turbulence effects were simulated through a Smagorinsky model. To study the particle dispersion and deposition in the modeled room, particles with different sizes (diameters of 10nm to 10 μm) were investigated. The simulated results for particle dispersion and deposition showed that the predictions of the present hybrid method were quite similar to the earlier LES-LBM. In addition, the predictions of the hybrid model for the particle deposition and dispersion were closer to the LES simulation results compared to those of the k-ε model. It was shown that the Brownian excitation is very important for nanoparticles and the number of deposited particles for 10nm particles is higher than those for the larger 100nm and 1μm particles. The deposition rate for 10 μm particles is also high due to the inertial effects.

Dispersion and deposition of non-spherical nano- and micro-particles suspended in turbulent flows was studied. Due to the non-spherical morphology, the coupled equations of translational and rotational motions of particles were solved and the corresponding particle trajectories were evaluated. For nano-particles with the scale comparable to the gas mean free path, the Brownian diffusion effects that becomes important was included in both translational and rotational motions. Particular attention was given to the interactions of nano-ellipsoidal particles and fluid motions at different scales. Examples of nano-ellipsoidal particle dispersion and deposition in ducts and respiratory tracks were presented and discussed. Such information is useful for understanding the transport processes of asbestos and nano-fibers in human airways for inhalation risk assessment studies.

In the present paper, a numerical study has been conducted to investigate the heat transfer from a constant temperature cylinder covered with metal foam. The cylinder is placed horizontally and is subjected to a constant mean cross-flow in turbulent regime. The Reynolds Averaged Navier-Stokes (RANS) and Darcy-Brinkman-Forchheimer equations are combined and used for flow analysis. The energy equation used assumes local thermal equilibrium between fluid and solid phases in porous media. The k-ω SST turbulence model is used to evaluate the eddy viscosity that is implemented in the momentum and energy equations. The flow in the metal foam (porous media) is in laminar regime. Governing equations are solved using the finite volume SIMPLEC algorithm. The effect of thermophysical properties of metal foam such as porosity and permeability on the Nusselt number is investigated. The results showed that using a metal porous layer with low porosity and high Darcy number in high Reynolds number turbulent flows markedly increases heat transfer rates. The corresponding increase in the Nusselt number is as high as 10 times that of a bare tube without the metal foam.

Recent rapid development of the carbon nanotubes (CNTs) industry has raised health concerns as these engineered particles have the appearance of asbestos, which is a well-known inhalation hazard. Compared to asbestos, CNTs have similar elongated rod shaped structure, while they are in nano-scale where the particle motion is markedly affected by Brownian diffusion. However, limited studies on Brownian dynamics of CNTs are available in the literature and the details of motions of these elongate ultrafine particles, and in particular, their transport and deposition processes are largely unknown. In this study, multi-scale analysis of transport and deposition of elongated particles in micro and nano-scales were performed. Particular attention was given to the differences and similarities of the physical mechanisms governing the particle/fiber motions at different length scales. The study was focused on revealing the details of the interaction between elongated particles at different scales and the fluid motions. Such information is very useful in understanding the transport processes of asbestos and nano-fibers in human airways for inhalation risk assessment studies.

In this study the hybrid RANS/LES turbulence model within the framework of the Lattice Boltzmann method (LBM) was used to study turbulent indoor airflows. In this approach the near wall region was simulated by the RANS model, while the bulk of the domain was analyzed using the LES model with the LBM approach. In the near wall layer where RANS was used, the k-ε turbulence model was employed. For the k-ε turbulence model in conjunction with the LBM two population balance equations for k and ε were used. The present simulation results for the airflow showed good agreement with the experimental data and the earlier numerical results for the hybrid RANS/LES. The results showed that the hybrid model properly predicted the large scale turbulence fluctuation velocities in the bulk of the flow region. In addition, the computational time for the hybrid model is less than that of the LES method.

The effectiveness of a novel actuation architecture developed to control flutter and post-flutter is investigated in this paper. To this purpose, the performance of an active control strategy in various operational conditions is experimentally examined. A physical prototype, consisting of a wing section with multiple spoilers mounted on an aeroelastic apparatus, has been designed and assembled to carry out open- and closed-loop operations. Wind tunnel aeroelastic testing are performed with a plunging and pitching apparatus specifically designed to simulating wing sections with prescribed stiffness characteristics, including torsional structural nonlinearities responsible of a stable nonlinear post-flutter limit cycle behavior. Five surface mounted spoilers located at 15% of the chord from the leading edge are used to control aeroelastic vibrations in pre- and post-flutter. The spoilers design, including selection of best size and chord position and considering the geometrical constraints, has been carried out by CFD simulation, with the objective of maximizing the aerodynamic pitching moment used to stabilize the lifting surface at the various speeds. The spoiler actuations are commanded by an active control system as to extend the flight region in the natural post-flutter condition. A simple PID algorithm is implemented to test the efficiency of the control system design to suppress flutter oscillation. A trial and error tuning of the gain has been executed on-site during the experimental campaign. Only the pitch angle is used as state feedback in the control laws to stabilize the system above the open-loop flutter velocity. Results and pertinent conclusions are outlined.

Indoor air quality (IAQ) is very important to human health and comfort as increasingly people spent most of their time in indoor environment. Numerical simulation of indoor airflows has become a significant tool for investigation of the indoor air quality. Cost effective computational methods with reasonable accuracy have the advantage of being more accessible to designers compared to more precise but expensive DNS methods. Recently developed Lattice-Boltzmann Method (LBM) has proved to be a powerful numerical technique for simulating fluid flows in various applications. In comparison with the conventional CFD methods, the advantages of LBM are: simple calculation procedure, simple and efficient implementation for parallel computation, and easy and robust handling of complex geometries. The indoor airflow is typically in turbulent flow regimes. Due to the high costs of more accurate direct numerical simulation (DNS) and large eddy simulation (LES), in this study the Reynolds Averaged Navier-Stokes (RANS) method was used for analyzing the turbulent flow conditions. The RANS governing equations, and in particular, the k-ε turbulence model was incorporated into the Lattice-Boltzmann computational method. The simulation results showed that the combined LBM-RANS provide a reasonably accurate description of the airflow behavior in the room at modest computational cost.

It is well known that the airflow is instrumental in the transmission of airborne infectious diseases in indoor environments. The airflow pattern in indoor environment is affected by the ventilation airflow, thermal plume around human bodies, human respiration, human motion and other activities. In this study, the CFD approach was used to simulate airflow field and particle transport in a room to provide exposure assessment for a heated breathing manikin with and without rotational motion. The simulation results indicated that the rotation of the manikin significantly impacts the thermal plume of the body and the associated transport of particulates.

A high-fidelity multibody dynamics model for simulating a backhoe digging operation is presented. The backhoe components including: frame, manipulator, track, wheels and sprockets are modeled as rigid bodies. The soil is modeled using cubic shaped particles for simulating sand with appropriate inter-particle normal and frictional forces. A penalty technique is used to impose both joint and normal contact constraints (including track-wheels, track-terrain, bucket-particles and particles-particles contact). An asperity-based friction model is used to model joint and contact friction. A Cartesian Eulerian grid contact search algorithm is used to allow fast contact detection between particles. A recursive bounding box contact search algorithm is used to allow fast contact detection between polygonal contact surfaces. The governing equations of motion are solved along with joint/constraint equations using a time-accurate explicit solution procedure. The model can help improve the performance of construction equipment by predicting the actuator and joint forces and the vehicle stability during digging for various vehicle design alternatives.

An explicit time integration multibody dynamics code is used to create a three-dimensional model of sand. Sand is modeled using discrete cubical particles with appropriate normal contact force and tangential friction force models. The model is used to predict the sand angle of repose and flow rate during discharge from a conical hopper. A penalty technique is used to impose normal contact constraints (including particle-particle, particle-hopper and particle-ground contact). An asperity-based friction model is used to model friction. A Cartesian Eulerian grid contact search algorithm is used to allow fast contact detection between particles. The governing equations of motion are solved along with contact constraint equations using a time-accurate explicit solution procedure. Parameter studies are performed in order to study the effects of the particle size and the orifice’s diameter of the hopper on the angle of repose and sand flow rate. The results of the simulations are validated using previously published experimental results.

Active vibration control of structures under earthquake excitation has attracted considerable attention in the recent years. In this study, attention was given to optimal preview control methodology for protection of building with and without base isolation systems against earthquakes. A three-story building model was used and several earthquake records including El Centro, Mexico City and Tabas earthquake records were used as excitation. Acceleration and displacement responses of the structure with active preview control were evaluated and the results are compared with those for the unprotected buildings. It was shown that using properly designed active preview control systems can effectively reduce the acceleration transmitted to structures during a major earthquake. The study was repeated for a base isolated structure. It was shown that that the using the information obtain from the preview sensors in the active control strategy would improve the system performance significantly. The influence of the preview time on the system performance was also studied. It was found that the range of preview time needed for improved performance is quite small but depends on the frequency contend of the earthquake excitation.

Synthetic jet actuators have been used for control of flow separation in high performance airfoils for increasing lift and low drag. The synthetic jets have zero net mass flux but impart net momentum to the flow. In this study, LES simulations was used to study the time history of outlet velocity profile and net momentum imparted to the flow by a synthetic jet actuator (SJA). The SJA studied is not symmetric and operates with the aid of a piezoelectric (PZT) ceramic circular plate actuator. A three-dimensional mesh for the computational domain of the SJA and surrounding volume was developed and was used to evaluate the details of the airflow conditions inside the SJA as well as at the outlet. The vibration of the PZT ceramic actuator was used as a boundary condition in the computational model to drive the SJA. Particular attention was given to the time evolution of the SJA outlet velocity profile. The time history of the outlet velocity profile of the synthetic jet was curve-fitted to an empirical equation. The resulting outlet velocity could be used as an inlet velocity for active close loop control of airflow separation around an airfoil at high angle of attack.

Transport and deposition of elongated particle and fibers have been of interest due to their pathological responses. In this work, the transport and deposition of elongated particles and ellipsoidal fibers were numerically simulated in a physiological realistic multi-level lung model. Detailed motion of the inhaled fibers and their interaction with the surrounding environment were reproduced by solving the system of coupled equations governing the elongated particles translational and rotational motions. Correlations between the deposition pattern, fiber characteristics, breathing rates, and airway morphology in human upper tracheobronchial airways were analyzed. The results were compared with experimental measurements, and good agreement was found.

Transport and deposition of inhaled asbestos fibers has been studied in the past few decades due to its pathological response in living being. Of the earlier study, in vitro and vivo experiments in human and animal subjects were conducted and measurements were made where carcinogenicity of these particles was investigated. In this work, the transport and deposition of elongated ellipsoidal fibers were numerically simulated in a physiological realistic multi-level lung model. Detailed motion of the inhaled fibers and their interaction with the surrounding environment were reproduced by solving the system of coupled nonlinear equations governing the fibers’ translational and rotational motion. This information has never been revealed in past studies. Correlations between the deposition pattern, fiber characteristics, breathing conditions, and airway morphology in human upper tracheobronchial airways were analyzed. The results were compared with experimental measurements, and carcinogenicity of these fibers was discussed.

Transport and deposition of ellipsoidal fibers in the human upper airways were analyzed using an asymmetric airway bifurcation model. The trachea and the first two generations (G0–G1) of the tracheobronchial tree were included in the study. The focus of the study was on prediction of transport and deposition of fibers and elongated particles. The laryngeal jet at the trachea entrance was modeled as an effective turbulence disturbance, and Reynolds stress transport turbulence model (RST) was used. For accurate modeling of the near wall airflow, the “two-layer zonal model” was used for boundary consideration, and the turbulence normal fluctuation close to wall is further corrected based on the “quadratic variation near wall model” (Tian and Ahmadi 2007). Lagrangian simulation of ellipsoidal fiber transport and deposition was developed where the coupled translational and rotational motions of the fibers were accounted for. The particle equations of motion included the hydrodynamic drag and torque, shear induced lift, gravitational sedimentation, and turbulence diffusion effects. The simulation results showed that the elongated fiber remained aligned with the main flow most of the time. On short duration occasions, the fibers rotated impulsively along their path. The fiber rotational motion was dependent on fiber geometry and the local flow shear. Fiber deposition pattern and deposition rate in the trachea and the first bifurcation were evaluated, and the results were compared with the experiments.

Particle dispersion and deposition over a square cylinder with different angles of incidence (α = 0°, 45°) in a channel flow was investigated numerically. A computational model using Lattice-Boltzmann Method (LBM) for flow simulation was developed. The interpolated bounce-back (IBB) boundary condition was applied to model the no-slip boundary conditions on curved boundary. The computational model was used to simulate the two-dimensional airflow field in the duct with obstructing square cylinder. A Lagrangian approach was used for simulation of spherical, solid particles suspended in the airflow in the duct. The Reynolds numbers were in the range of laminar. The formation of the von Karman vortex sheet behind the cylinder was predicted by the present LBM simulation. It was shown that the periodicity of the simulated vortex street agrees well with available experimental data. Transport and deposition of 1 μm to 100 μm particles in the duct were studied. The instantaneous flow field was used to evaluate the particle trajectories. The forces included in the particle equation of motion were drag, lift, gravity, and Brownian. The simulation results shows that the particle deposition efficiency decreases when the angle of incidence is increased from 0° to 45° and also more vigorous vortex shedding was observed at α = 45°.