Propeller-Induced Seabed Scour: A Review of Hydrodynamic Mechanisms, CFD Modeling, and Coastal Engineering Implications

Describes the modeling of the statics and dynamics of a towed undersea vehicle, taking the reader through the process from CFD modeling, correlation using wind tunnel test data, and in-water steady state and manoeuvering validation. A Vehicle Control Technologies (VCT) model that had previously been developed without the benefit of modern CFD methods is compared to model scale wind tunnel force and moment data as well as full-scale in-water data. The hydrodynamic model is then updated with recent technology and again compared to the same model scale and full-scale data. Advancements in hydrodynamic technology over the last few years have taken hydrodynamics to a new plateau of modeling accuracy, which rivals those of experimentally based approaches, and are accomplished at a much lower cost. In the new methodologies, contributions to the body and fin surfaces are computed using a combination of techniques, which are both CFD based and semi-analytical. The CFD code developed by VCT tracks the hull vorticity and computes the point where the hull wake is shed based on a method similar to that used to compute the Kutta condition for a wing. Interference effects, such as fin-to-fin and fin-to-body, are now computed using the vorticity based CFD models. In addition to improving the static terms to the equations of motion, the CFD code improves the computation of the added mass terms and the computation of damping effects due to the vehicle hull. The CFD based model has been correlated to wind tunnel force and moment data. Wind tunnel data included body build-up configurations as well as the fully appended vehicle. The body build up process is important to understanding the effect of wing upwash on the control surfaces. The in-water comparisons for pitch angle and sternplane angle (both the steady state trim conditions and the transient response during dynamic manoeuvers) were made without further adjustments to the wind tunnel correlated model.

A computational fluid dynamics model was developed to represent high‐solids enzymatic hydrolysis. This model accounted for the transient and multiphase (solids‐slurry) nature of the high‐solids enzymatic hydrolysis process. The model investigated the effect of slurry viscosity, rotational speed, and two impeller configurations on the distribution of insoluble solids. Initial CFD results identified segregation of the velocity contours for the non‐Newtonian slurry, which could potentially affect the reactor performance. The multiphase, transient CFD simulations showed that the first impeller configuration delayed the distribution of solids, and compartmentalized mixing in the reactor. The second impeller configuration, meanwhile, improved solids mixing and hydrolysis, while using lower rotational speeds (and thus, energy). The second impeller configuration also expanded the size of the pseudo‐cavern between impellers, which is critical for better dispersion of the solids. The CFD trends of the second impeller configuration were experimentally verified by conducting fed‐batch, high‐solids enzymatic hydrolysis trials with pretreated lignocellulose. The experimental results showed that the second impeller configuration provided better mixing of the non‐Newtonian slurry and enhanced solids‐enzyme interactions, leading to improved glucan‐to‐glucose conversion. This work illustrates that a transient multiphase CFD model can provide valuable insights into the design and optimization of high‐solids enzymatic hydrolysis reactors. The CFD model has identified pathways to improve the distribution of solids while reducing the energy needed for mixing. The CFD model can also guide experimental and design work to scale up these reactors from the laboratory to pilot and commercial scale.

A coupled combustion and hydrodynamic model for the prediction of waterwall tube overheating of supercritical boiler

Turning and zigzag maneuverability investigations on a waterjet-propelled trimaran in calm and wavy water using a direct CFD approach

The expansion of laser-ablated plasma plume into an ambient atmosphere is a very complex phenomenon. It includes different stages, each with different underlining physics such as heating and melting of the surface of material, evaporation, ionization, and expansion of the produced plasma. Various numerical models have been developed to capture the behavior of the ablated plasma on different time and space scales. Treating a plasma as a conducting fluid has the advantage of capturing its overall macroscopic dynamics on long timescales [1] . To improve our understanding of the plasma expansion, a hydrodynamic two-fluid two-temperature CFD model has been developed within the open-source OpenFOAM software toolbox utilizing multiphaseEulerFoam solver [2] . The plasma is treated as two fluids, one for ions and another for electrons [1] . The ultimate goal is to implement many relevant physical processes in the OpenFOAM CFD model in order to increase its accuracy in capturing specific effects of the laser ablation, blow-off, and expansion of a plasma plume. The CFD model has been validated against experimental and computational data. The modeling of laser ablation of pure and composite materials has been carried out. The energy transfer by electrons to ions and the time and space evolution of densities, velocities, and pressures for both electronic and ionic fluids are investigated.

CFD modelling of hydrodynamics and degradation kinetics in an annular slurry photocatalytic reactor for wastewater treatment

Recent research revealed the potential of tidal energy in the central coastal region of the Colombian Pacific. Buenaventura City, located in the Valle del Cauca department in Colombia, has an important opportunity to develop tidal power technologies near its marine coastal areas. This research implemented a 3D hydrodynamic model for simulating the hydrodynamics of the Buenaventura Bay to provide data as input for evaluating the hydraulics of a tidal barrage without sluicing through CFD modeling. According to the results, the velocities across the gates during Syzygy (April 2021) showed impressive velocities between 9 and 11 m/s, which suggest a high possibility of producing electricity through tidal turbines. The mean behavior of velocities in the gates pointed to values of 3 and 5 m/s in most of the cases. The results during the Stoa condition were interesting because flow velocities higher than 1 m/s were not expected. This is promising because the plant might produce electricity even during the Stoa condition. For the first time, the results of this research suggest that there exists a high possibility of implementing tidal barrage plants in Buenaventura City, Colombia.

The high cellulosic content of rice husk can be utilized as a feedstock for pulp and biofuel. Pretreatment is necessary to break the bonds in the complex lignocellulose matrices addressing the cellulose access. This work aims to utilize the rice husk using dilute acid and alkaline pretreatment experimentally and CFD modeling. The study consists of three series of research. The first stage was the dilute acid pretreatment with sulfuric acid concentration of 1% to 5% (v/v) at 85°C for 60 minutes, and alkaline pretreatment with NaOH concentration of 1% to 5% (w/v) at 85oC for 30 minutes separately. The second stage used the combination of both pretreatment. Moreover the last stage of research was hydrodynamic modeling of pretreatment process by CFD (ANSYS FLUENT 16). The experimental results showed that the lowest lignin content after acid pretreatment was about 10.74%. Alkaline pretreatment produced the lowest lignin content of 4.35%. The highest cellulose content was 66.75 % for acid-alkaline pretreatment. The lowest content of lignin was about 6.09% for acid-alkaline pretreatment. The lowest performance of alkaline pretreatment on HWS (hot water solubility) of about 7.34% can be enhanced to 9.71% by using a combination alkaline-acid. The combined pretreatments result hemicellulose of about 9.59% (alkaline-acid) and 9.27% (acid-alkaline). Modeling results showed that the mixing area had the minimum pressure of about -6250 Pa which is vortex leading minimum efficiency of mixing. The rice husk flowed upward to the upper level and mixed with reagent in the perfect mixing.

The article presents a methodology for the theoretical assessment of the processes of loosening and compaction of the soil with a working tool based on pressure distribution patterns in the soil stratum obtained using the computational fluid dynamic model (CFD model). A computational fluid dynamics model is developed to assess the stress-strain state of the soil and soil particles' movement, implemented in the FlowVision computer program. As a model, the FlowVision Free Surface model is adopted, in which the Navier-Stokes equations, the transfer equations of turbulent functions, and the transfer equation for the filling function are solved. The implementation of this model made it possible to establish three-dimensional pressure distribution patterns, based on which zones of deformation, loosening, and compaction in the soil were determined in interaction with a vertical working tool. The implementation of this methodology will theoretically justify the geometric parameters of tillage tools and machines, taking into account the conditions for forming the required quality of tillage by loosening and compaction.

A 2-D full-coupled hydrodynamic and morphology CFD model is developed and improved based on OpenFOAM®. Two physical experiments are used to validate the model: breaking solitary wave on a sloping beach (Sumer et al. 2011); local scour beneath a pipeline under steady flow (Mao 1986). The numerical model is based on incompressible Reynolds-averaged Navier-Stokes equations and incorporated with volume of fluid (VOF) method, k-omega turbulence closure, and sediment transport model (both for bed load transport and suspended load transport). The bed evolution is tracked by dynamic mesh method. A new near wall treatment for suspended load transport, which proposed by Liu (2013), is implanted in this model. The hydrodynamic model is validated against the rigid-bed case of the breaking solitary wave experiment. The numerical results of wave surface elevation and bed shear stress agree well with those obtained from the experiments. Then the sediment transport model is validated under both solitary wave and steady flow experiments. The quantitative agreement between computed sediment bed profile and experiment results are satisfactory, despite a slight underestimation of the erosion depth in solitary wave case. The results show that the numerical model can well simulate hydrodynamic and morphology involved in coastal and ocean engineering problems, such as beach erosion and local scour under subsea pipeline.

CFD modeling of a fixed-bed biofilm reactor coupling hydrodynamics and biokinetics

CFD Modeling and Simulation of Hydrodynamics in a Fluidized Bed Chamber with Experimental Validation

Validation of a CFD model of Taylor flow hydrodynamics and heat transfer

Hydrodynamics in liquid-solid circulating fluidized beds (LSCFBs) are modelled and simulated by computational fluid dynamic (CFD) technique. Turbulence model and kinetic theory descriptions of granular flow are incorporated in the governing equations to model the high Reynolds number two-phase flows with strong particle-particle interactions in LSCFBs. Liquid-solid upflows under wide operating conditions, different particle properties and different bed dimensions are investigated by time-dependent simulations using commercial software, FLUENT 4.5.6. The model predictions show good agreements with the experimental data and reasonable trends when different fluids/solids and bed dimensions are applied. Stronger nonuniformities in flow structures are found in larger particle systems, with larger fluid/solids density ratios and/or larger diameter columns. On a modelise et simule l'hydrodynamique dans des lits fluidises circulants liquide-solides (LSCFB) par mecanique des fluides numeriques (CFD). On a incorpore aux equations d'echange un modele de turbulence et un modele de theorie cinetique d'ecoulement granulaire pour simuler les ecoulements biphasiques a nombres de Reynolds eleves avec de fortes interactions particule-particule dans les LSCFB. Les ecoulements ascendants liquide-solides pour une vaste gamme de conditions operatoires, differentes proprietes de particules et differentes dimensions de lits sont etudies par des simulations instationnaires a l'aide du logiciel commercial FLUENT 4.5.6. Les predictions de modeles montrent un bon accord avec les donnees experimentales et des tendances raisonnables lorsque differents fluides/solides et dimensions de lits sont appliques. Des non-uniformites plus fortes dans les structures d'ecoulement ont ete trouvees dans les systemes a larges particules, avec les rapports de masse volumique fluide/solides ou les colonnes de diametres les plus grands.

Electrodialysis (ED) cells are based on the selective transport of ions through membranes which ideally exclude the co-ions, so that when a potential difference is applied to the cell all ions are transported in solution but only the counter ions can cross the membrane. Thus, concentration polarization occurs in solutions adjacent to membrane surfaces due to the different transport number between the membrane and the solution. The concentration profiles formed in the solution near the membrane depends on the mass transport fluxes and hydrodynamic pattern in the channel; operating conditions and geometrical configuration of the cell affect greatly the concentration polarization [1]. Therefore, the performance of ED cells depends not only on the membrane properties but also on the electrolyte hydrodynamics being important to provide an adequate flow patter avoiding channeling, stagnant zones, jet formation, among others flow deviations. Keeping a homogeneous flow patter minimizes variations of mass transfer fluxes and current density over the membrane surface preventing high polarization zones that could give rise to water dissociation, low efficiency and premature membrane failure. The examination of relevant mass transport mechanisms by modelling can help to evaluate the effect of design characteristics and operating conditions on the performance of an electrodialysis cell through the analysis of concentration, potential and current density distributions. In this task, CFD has proven to be a valuable tool for the analysis of flow and mass transfer in membrane separation systems [2]. Therefore, this work presents the modelling of a laboratory ED cell coupling hydrodynamics and mass transport, taking into consideration changes of Donnan potential. The flow pattern inside channels of ED cell were obtained by 3D CFD modeling and the results were used to calculate the residence time distribution (RTD) to compare with experimental RTD. The hydrodynamic behavior was used then to solve the mass transport model to obtain a description of the concentration distribution of each of the ionic species in the cell, as well as of the amounts derived as fluxes of each of the components, current density and Donnan potentials at every point of the membrane.[1] Gurreri L., Tamburini A., Cipollina A., Micale G., Ciofalo M., CFD prediction of concentration polarization phenomena in spacer-filled channels for reverse electrodialysis J. Membr. Sci. 468, 133–148 (2014).[2] Fimbres-Weihs G.A., Wiley D.E., Review of 3D CFD modeling of flow and mass transfer in narrow spacer-filled channels in membrane modules, Chem. Eng. Process. 49 759–781 (2010).