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The necessity for precise prediction of penetration depth in the context of electron beam welding (EBW) cannot be overstated. Traditional statistical methodologies, including regression analysis and neural networks, often necessitate a considerable investment of both time and financial resources to produce results that meet acceptable standards. To address these challenges, this study introduces a novel approach for predicting EBW penetration depth that synergistically combines computational fluid dynamics (CFD) modelling with artificial neural networks (ANN). The CFD modelling technique was proven to be highly effective, yielding predictions with an average absolute percentage deviation of around 8%. This level of accuracy is consistent across a linear electron beam (EB) power range spanning from 86 J/mm to 324 J/mm. One of the most compelling advantages of this integrated approach is its efficiency. By leveraging the capabilities of CFD and ANN, the need for extensive and costly preliminary testing is effectively eliminated, thereby reducing both the time and financial outlay typically associated with such predictive modelling. Furthermore, the versatility of this approach is demonstrated by its adaptability to other types of EB machines, made possible through the application of the beam characterisation method outlined in the research. With the implementation of the models introduced in this study, practitioners can exert effective control over the quality of EBW welds. This is achieved by fine-tuning key variables, including but not limited to the beam power, beam radius, and the speed of travel during the welding process. [ABSTRACT FROM AUTHOR]

This paper investigates modelling strategies on the prediction of lift and drag coefficients of a NACA0012 airfoil at Reynolds number of 360,000. Two computational methods are employed; namely Navier-Stokes equation and panel method, by using different tools for computing lift and drag coefficients. The obtained results are compared against experiment in order to assess the accuracy of each technique. Two turbulence models are employed; Reynolds stress model, which is not based on Boussinesq assumption and accounts for flow anisotropy and realizable model which is based on the Boussinesq assumption for computing Reynold stresses. Grid independent solution is produced using the 2-D URANs by employing the fitting method and the obtained lift and drag coefficients are compared against experiment. The fitting method is found to be efficient in saving computational time and power. It is also found that Boussinesq approximation is efficient in predicting lift coefficient. However, the 3rd order panel method produced a remarkably accurate drag coefficient compared to other investigated computational models. Combining the findings of this paper with the existing computational methods in the literature would significantly in improve the accuracy of predicting lift and drag coefficients and may significantly enhance the accuracy of simulation of several aerodynamics applications.

Computational fluid dynamics (CFD) is an established approach to study flow behaviour. Despite advances in mathematical numerical modelling in recent decades, accurately predicting the turbulent flow behaviour of steel using CFD remains a challenge. In the continuous casting process, two main flow control systems are employed to transfer liquid steel from the tundish to the mould, namely stopper control and slide gate control. In additional to these two main flow control systems, the casting nozzle geometries, casting rate, and casting mould dimensions vary considerably, and this complexity makes it difficult to precisely simulate turbulent flow in the casting channel. In this paper, examples are presented showing how different turbulence models influence the simulation results, using the latest version of the open source CFD simulation software OpenFOAM. Prior to the CFD modelling, RHI Magnesita's water modelling facilities in Leoben (Austria) were used to validate the state-of-the-art turbulence models selected for a particular casting nozzle geometry and flow control system. [ABSTRACT FROM AUTHOR]

The necessity for precise prediction of penetration depth in the context of electron beam welding (EBW) cannot be overstated. Traditional statistical methodologies, including regression analysis and neural networks, often necessitate a considerable investment of both time and financial resources to produce results that meet acceptable standards. To address these challenges, this study introduces a novel approach for predicting EBW penetration depth that synergistically combines computational fluid dynamics (CFD) modelling with artificial neural networks (ANN). The CFD modelling technique was proven to be highly effective, yielding predictions with an average absolute percentage deviation of around 8%. This level of accuracy is consistent across a linear electron beam (EB) power range spanning from 86 J/mm to 324 J/mm. One of the most compelling advantages of this integrated approach is its efficiency. By leveraging the capabilities of CFD and ANN, the need for extensive and costly preliminary testing is effectively eliminated, thereby reducing both the time and financial outlay typically associated with such predictive modelling. Furthermore, the versatility of this approach is demonstrated by its adaptability to other types of EB machines, made possible through the application of the beam characterisation method outlined in the research. With the implementation of the models introduced in this study, practitioners can exert effective control over the quality of EBW welds. This is achieved by fine-tuning key variables, including but not limited to the beam power, beam radius, and the speed of travel during the welding process.

This paper investigates modelling strategies on the prediction of lift and drag coefficients of a NACA0012 airfoil at Reynolds number of 360,000. Two computational methods are employed; namely Navier-Stokes equation and panel method, by using different tools for computing lift and drag coefficients. The obtained results are compared against experiment in order to assess the accuracy of each technique. Two turbulence models are employed; Reynolds stress model, which is not based on Boussinesq assumption and accounts for flow anisotropy and realizable model which is based on the Boussinesq assumption for computing Reynold stresses. Grid independent solution is produced using the 2-D URANs by employing the fitting method and the obtained lift and drag coefficients are compared against experiment. The fitting method is found to be efficient in saving computational time and power. It is also found that Boussinesq approximation is efficient in predicting lift coefficient. However, the 3rd order panel method produced a remarkably accurate drag coefficient compared to other investigated computational models. Combining the findings of this paper with the existing computational methods in the literature would significantly in improve the accuracy of predicting lift and drag coefficients and may significantly enhance the accuracy of simulation of several aerodynamics applications. [ABSTRACT FROM AUTHOR]

Since a combined harvester’s grain-cleaning method depends on the pneumatic separation of grain and chaff, the airflow’s aerodynamic forces significantly affect cleaning efficiency. Based on buckwheat’s theoretical and mechanical properties, a new threshing drum with cleaning key parts was developed to reduce the variability of cleaning efficiency of buckwheat community threshers caused by inefficient threshing and accumulation of residue within the threshing system. This cleaning arrangement includes two wind speed inlets, each composed of four thin pipes of the same length as the threshing drum. The computational fluid dynamics modelling approach simulated the threshing and cleaning performance at different wind velocities within the threshing unit. The results showed that when the two inlets work simultaneously and adopt different wind speeds, i.e., 12 m/s and 15 m/s, the wind speed is higher than the critical value of the floating rate buckwheat kernel. Under this condition, the wind speed inlet area was increased, and the flow field velocity between the threshing drum and the concave grid plate ranged from 3.8 m/s-8.3 m/s. The flow velocity below the plate ranged from 7 m/s-15 m/s, higher than the floating speed of buckwheat kernels, which was the best choice. Based on these simulation results, a centrifugal fan was designed, which meets the buckwheat thresher’s cleaning performance.

Bioreactor‐based processes are the method of choice for efficient expansion of cells in a controlled setting. However, induced pluripotent stem cells (iPSCs) have proven to be extremely sensitive to the bioreactor hydrodynamic environment, making the use of suspension bioreactors to produce quality‐assured cells at clinical and commercial scales very challenging. The PBS vertical‐wheel (VW) bioreactor combines radial and axial flow components to produce uniform hydrodynamic force distributions, making it a promising platform to overcome the scale‐up challenges associated with iPSCs. In this study, hydrodynamic characterization through computational fluid dynamics modelling of VW bioreactors was performed. Analysis of these models proved that important volume average hydrodynamic variables could be maintained throughout scale‐up from the 0.1 L to the 15 L VW bioreactor scale. Each bioreactor scale (0.1, 0.5, 3, and 15 L) was modelled at a variety of agitation rates, leading to the generation of scale‐up correlation equations. These equations allow operators to define a working range of hydrodynamic variables at one scale and calculate the corresponding agitation rates at other modelled scales. A suggested operating range of agitation rates was determined for the successful culture of iPSCs in the VW bioreactor at each scale, corresponding to constant volume average energy dissipation rate. Agitation rates from the 0.1 and 0.5 L VW bioreactor scale were experimentally tested to biologically validate the suggested range. High cell‐fold expansion, healthy aggregate morphology, growth, and uniformity were demonstrated for all conditions tested within the suggested working range. [ABSTRACT FROM AUTHOR]

A backward facing step (BFS) flow has been investigated extensively by the research community experimentally and computationally due to its significant flow features because of the presence of the separation-reattachment mechanism. The strength of this mechanism varies based on the Reynolds number (RN). For turbulent flow at low RN, the separation-reattachment mechanism computations may be expensive due to high requirements of fine grid which varies based on the employed turbulence model. Several classes of turbulence models have been attempted for capturing complex fluid flow phenomena, namely zero, one, two, three, four and seven equation models. Selected turbulence models from each class have been employed in this paper in order to predict the reattachment length behind BFS at RN of 37,000. The grid independent solution is obtained using modified general Richardson method based on three relatively coarse grids which significantly reduces the computational cost. It is found that the predicted reattachment length for employed turbulence models agrees well with experiment and is considered as a grid independent solution. The visualization of computational domain on the wind tunnel shows similar trends for flow developed in the region of reattachment length. This work can substantially reduce cost of computations for the prediction of reattachment length in BFS flow problem and shows how closely turbulence models perform when grid independent solution is obtained. [ABSTRACT FROM AUTHOR]

Coronary arterial disease, as the most devastated cardiovascular disease, is caused by the atherosclerosis in the coronary arteries, which blocks the blood flow to the heart, resulting in the deficient supply of oxygen and nutrition to the heart, and eventually leading to heart failure. To date, haemodynamic mechanisms for atherosclerosis development are not fully understood although it is believed that the haemodynamic disturbance at the region of the arterial bifurcation, particular, bifurcation angle, plays an important role in the atherosclerosis development. In this study, two types of computational fluid dynamics models, lesion-specific and idealized models, combined with the computer tomography imaging techniques, are used to explore the mechanism of formation and distribution of the atherosclerosis around the bifurcation of left coronary artery and its association with the bifurcation angle. The lesion-specific model is used to characterize the effect of personalized features on the haemodynamic performance, while the idealized model is focusing on the effect of single factor, bifurcation angle, on the haemodynamic performance. The simulated results from both types of the models, combined with the clinical observation, revealed that the three key areas around the bifurcations are prone to formation of the atherosclerosis. Unlike the idealized models, lesion-specific modelling results did not show the significant correlation between the wall shear stress and bifurcation angle, although the mean value of the wall shear stress in smaller bifurcation angles (less than 90°) is higher than that with larger bifurcation angles (greater than 90°). In conclusion, lesion-specific computational fluid dynamics modelling is an efficient and convenient way to predict the haemodynamic performance around the bifurcation region, allowing the comprehensive information for the clinicians to predict the atherosclerosis development. The idealized models, which only focus on single parameter, may not provide the sufficient and reliable information for the clinical application. A novel multi-parameters modelling technique, therefore, is suggested to be developed in future, allowing the effects of many parameters on the haemodynamic performance to be evaluated. [ABSTRACT FROM AUTHOR]

In this article, a numerical methodology for assessing combustion noise in compression ignition engines is described with the specific purpose of analysing the unsteady pressure field inside the combustion chamber. The numerical results show consistent agreement with experimental measurements in both the time and frequency domains. Nonetheless, an exhaustive analysis of the calculation convergence is needed to guarantee an independent solution. These results contribute to the understanding of in-cylinder unsteady processes, especially of those related to combustion chamber resonances, and their effects on the radiated noise levels. The method was applied to different combustion system configurations by modifying the spray angle of the injector, evidencing that controlling the ignition location through this design parameter, it is possible to decrease the combustion noise by minimizing the resonance contribution. Important efficiency losses were, however, observed due to the injector/bowl matching worsening which compromises the performance and emissions levels. [ABSTRACT FROM AUTHOR]

Summary Fires originating in informal settlements (ie, slums, ghettos, shantytowns, squatter camps) spread rapidly, due to the presence of densely packed, highly combustible dwellings, thereby making these communities inherently susceptible to large conflagrations. By the time, the fire brigades are notified and can get to the scene of the fire, the resulting conflagrations can be large. Thus, it is necessary to equip communities with the ability to combat smaller fires, although it is acknowledged that this is not ideal. Previous full‐scale testing and firefighter experience have shown that water application through 'bucket brigades' can be very effective at suppressing fires. In this article, a model is developed for approximately quantifying the amount of water, and discharge rate, that is, required for communities to suppress fires of various sizes using bucket brigades. This is done to answer the question: based on the water supply infrastructure in an area could a community put out post‐flashover fires of certain sizes? If this is not feasible, it would highlight the importance of communities having readily available pre‐filled water buckets at homes. The model presented is developed in fire dynamics simulator and is calibrated based on full‐scale experiments utilizing the bucket brigade technique. It is shown that standpipe discharge rates of 23 to 40 lpm are suitable for fire sizes of around 3.85 MW, based on a dwelling size of 2.4 x 3.6 x 2.4 m. This means that in communities with a single stand‐pipe (water supply point) with flow rates less than 23 lpm, that fires greater than 3.85 MW (as produced by a home of 2.4 x 3.6 m with a timber fuel load of 25 kg/m2) cannot be suppressed in time without resulting in substantial fire spread to adjacent dwellings. [ABSTRACT FROM AUTHOR]

In this study, we present the design considerations of a device to assist in the potential treatment of hemorrhagic stroke with the aim of stopping blood from flowing out into brain tissue. We present and model three designs for the clinical scenarios when saccular aneurysms rupture in the middle cerebral artery in the brain. We evaluate and model these three designs using computer aided design software, SolidWorks, which allows the devices to be tested using finite element analysis and also enables us to justify that the materials chosen were suitable for potential use. Computational fluid dynamics modelling were used to demonstrate and analyse the flow of blood through the artery under conditions of normal and ruptured states. We conclude that our device could potentially be useful in the treatment of hemorrhagic stroke, and the modelling process is useful in assisting in determining the performance of our devices. [ABSTRACT FROM AUTHOR]

In the present study, novel in-situ oxidation precipitation of ferrous hydroxide method is used to synthesized Fe 3 O 4 nanoparticles and Polyethylene glycol 200 is used for covalent functionalization. Various characterizations tests (FESEM, EDX, XRD, FTIR, HRTEM) were performed, and the Polyethylene glycol treated Iron oxides functionalization was confirmed. Thermal conductivity, density, specific heat, and viscosity were experimentally assessed and validated using the correlations that were available. The corresponding improvements in thermophysical characteristics were 13.35%, 0.06%, 0.37%, and 20.9% at 0.1 wt% and 35°C. UV–vis spectroscopy and Zeta protentional was used to check the stability of nanofluids and found that nanofluid was stable for 30 days. A flat plate solar collector was experimentally installed, and the thermal performance of collector was calculated using ferrofluid under ASHRAE standard 93–2003 at different heat flux intensities (597,775,988 W/m2), mass flow rates ((0.0133, 0.0200, 0.0266 kg/s), inlet fluid temperature (30–50°C) and weight concentrations (0.025,0.05,0.075,0.1%). The highest thermal efficiency enhancement of 13.83% was noticed. Moreover, the ANSYS-CFD model was used for the numerical analysis of the thermal performance of flat plate collector at the same environmental conditions, and a maximum difference of 8.33% at 0.1 wt% was noticed in comparison with experimental data. • Nanofluid was synthesized using in-situ oxidation method and confirmed with different characterization technique. • Thermophysical properties of Nanofluids with different weight concentrations were measured experimentally. • Thermal performance of FPSC was evaluated using ferrofluid and found 13.83% enhancement. • A maximum difference of 8.33% at 0.1 wt% was noticed in comparison with experimental data when ANSYS-CFD model was used. [ABSTRACT FROM AUTHOR]

Solid-to-water proportion decides the effectiveness of paste backfill in terms of transportation characteristics during mine backfilling. This article highlights various laboratory tests conducted to determine the optimum solid-to-water ratio. Also, numerical simulation was carried out using computational fluid dynamics technique (ANSYS FLUENT) to understand the slump lifting process and variation in volume of the paste with time. The optimum slump and spread for lead-zinc mill tailings paste were in the range 190-200 mm and 330-340 mm respectively. The optimum water content in the paste fill for this study was found to be 23 wt%. Results show that the solid percentage is inversely related with slump and spread. Also, an optimum slump lifting speed needs to be maintained for accurate values of slump and spread. [ABSTRACT FROM AUTHOR]

The wave loads and the resulting motions of floating wave energy converters are traditionally computed using linear radiation–diffraction methods. Yet for certain cases such as survival conditions, phase control and wave energy converters operating in the resonance region, more complete mathematical models such as computational fluid dynamics are preferred and over the last 5 years, computational fluid dynamics has become more frequently used in the wave energy field. However, rigorous estimation of numerical errors, convergence rates and uncertainties associated with computational fluid dynamics simulations have largely been overlooked in the wave energy sector. In this article, we apply formal verification and validation techniques to computational fluid dynamics simulations of a passively controlled point absorber. The phase control causes the motion response to be highly nonlinear even for almost linear incident waves. First, we show that the computational fluid dynamics simulations have acceptable agreement to experimental data. We then present a verification and validation study focusing on the solution verification covering spatial and temporal discretization, iterative and domain modelling errors. It is shown that the dominating source of errors is, as expected, the spatial discretization, but temporal and iterative errors cannot be neglected. Using hexahedral cells with low aspect ratio and 30 cells per wave height, we obtain results with less than 5% uncertainty in motion response (except for surge) and restraining forces for the buoy without phase control. The amplified nonlinear response due to phase control caused a large increase in numerical uncertainty, illustrating the difficulty to obtain reliable solutions for highly nonlinear responses, and that much denser meshes are required for such cases. [ABSTRACT FROM AUTHOR]

The safe removal of disease-carrying human waste is the objective of all sanitation systems and the limiting of air pressure transients within the system remains a significant part of current codes and regulations. The water trap seal offers fundamental protection and is the system’s sole barrier between the public sewer network and habitable space inside a building. Modelling water trap seal responses to air pressure fluctuations offers an opportunity to analyse whole system performance, but the quality of the data depends on the accuracy of the modelling technique and that of the defining inputs. AIRNET, a 1D Method of Characteristics based model, enables rapid whole system testing; however, the present boundary condition for the water trap seal within the model is based solely on steady state conditions, ignoring system dynamics. Computational fluid dynamics offers an opportunity to numerically evaluate the flow patterns within the trap seal in response to applied air pressure transients. This research confirms the importance of the rate of rise, and hence frequency of air pressure transients incident on water trap seals and relates this to potential vulnerabilities of different device geometries, particularly the ratio between inner and outer wall length. The research led to the development of a dynamic velocity decrement model encapsulating unsteady friction and separation losses linked to device geometry for the first time. The development of a frequency-dependent internal energy term Δv, suitable for inclusion in AIRNET provides the capability to predict more realistic water trap response to air pressure transients over a range of air pressure transient frequencies likely to cause problems: 1 Hz to 8 Hz.Practical application: Whole system modelling can greatly improve the ability of design engineers to fully simulate the operation of a building drainage system in a realistic way. The work described in this paper improves the accuracy of whole system models by evaluating water dynamic responses to air pressure transients using a range of techniques including computational fluid dynamics and more traditional 1D finite difference method of characteristics models. The work also paves the way for more robust evaluation of building drainage products through in-depth investigation of the fluid mechanics associated with their operation. [ABSTRACT FROM AUTHOR]

Carbon capture and storage (CCS) is a technology that has been proposed to reduce what are perceived to be excessive concentrations of carbon dioxide (CO2) in the atmosphere. CCS will require the transportation of CO2 from the capture locations to the storage sites via pipelines. To ensure safety, an accurate prediction of CO2 decompression following pipeline fracture is crucial for the design and operation for these projects. A multi-phase CO2 pipeline decompression model using computational fluid dynamics (CFD) techniques is presented in this paper. The GERG-2008 equation of state (EOS) is employed to describe the properties of vaporand liquid phases. A phase change model using a mass transfer coefficient to control the inter-phase mass transfer rateis implemented into the CFD code. By varying the mass transfer coefficient, the effect of delayed nucleation on the decompression wave speed can be investigated. The proposed multi-phase CFD decompression modelis validated against the experimental data from a shock tube test. The performance of the proposed model is also compared with that of the Homogeneous Equilibrium Model (HEM). In addition, the influence of delayed nucleation on CO2 decompression characteristics is discussed and an optimum mass transfer coefficient for CO2 depressurization is obtained. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Syringomyelia (a spinal cord cyst) usually develops as a result of conditions that cause cerebrospinal fluid (CSF) obstruction. The mechanism of syrinx formation and enlargement remains unclear, though previous studies suggest that the fluid enters via the perivascular spaces (PVS) of the penetrating arteries of the spinal cord, and that alterations in the CSF pulse timing and pressure could contribute to enhanced PVS inflow. This study uses an idealised computational model of the PVS to investigate the factors that influence peri-arterial fluid flow. First, we used three sample patient-specific models to explore whether changes in subarachnoid space (SAS) pressures in individuals with and without syringomyelia could influence PVS inflow. Second we conducted a parametric study to determine how features of the CSF pulse altered perivascular fluid, including alterations to timing and magnitude of the peak SAS pressure, the timing of reversal from high to low pressure (diastolic phase), and the area under the pressure–time curve. The model for the patient with syringomyelia had higher net CSF inflow to the PVS than the two subjects without syringomyelia. In the parametric study, only increasing the area under the high pressure region of the SAS pulse substantially increased PVS inflow, when coupled with a temporal shift in arterial and SAS pulses. This suggests that a period of sustained high SAS pressure while arterial diameter is low may increase net CSF pumping into the PVS. [ABSTRACT FROM PUBLISHER]

Concentration polarization is one of the main challenges of membrane-based processes such as power generation by reverse electrodialysis. Spacers in the compartments can enhance mass transfer by reducing concentration polarization. Active spacers increase the available membrane surface area, thus avoiding the shadow effect introduced by inactive spacers. Optimizing the spacer-filled channels is crucial for improving mass transfer while maintaining reasonable pressure losses. The main objective of this work was to develop a numerical model based upon the Navier–Stokes and Nernst–Planck equations in OpenFOAM, for detailed investigation of mass transfer efficiency and pressure drop. The model is utilized in different spacer-filled geometries for varying Reynolds numbers, spacer conductivity and fluid temperature. Triangular corrugations are found to be the optimum geometry, particularly at low flow velocities. Cylindrical corrugations are better at high flow velocities due to lower pressure drop. Enhanced mass transfer and lower pressure drop by elevating temperature is demonstrated.

Over the next few years, the engineering support required to meet the UK Nuclear Decommissioning Authority's strategic targets for redistribution of materials will ramp up significantly. To carry out these activities efficiently requires innovative solutions to be applied. This paper describes an approach for the transport of certain categories of heat generating materials, which offers operational and payload benefits. For the transport of certain materials, the use of a relatively small package is required for handling purposes, carrying internal product cans of material containing fissile product. It is proposed that 'INS3578' packages could be used. The packages are to be contained within an ISO container. Owing to the heat generating nature of some of the material to be transported, consideration must be given to the evacuation of heat from the container. A passively cooled container has the advantage of not requiring the complication of a forced ventilation system and refrigeration plant. This has operational, licensing and security benefits. A concept study undertaken to investigate a passively cooled container is described, including options that have been considered and the results from calculations undertaken to determine the package temperature. The results from the concept study suggest that with further work and further consideration of the heat load to be placed inside the container, the concept of a passively cooled ISO container for the transport of material might be a viable option. [ABSTRACT FROM AUTHOR]

Since November 2009, Germany's first full-scale ozonation plant for tertiary treatment of secondary effluent is in continuous operation. A kinetic model was developed and combined with the commercial computational fluid dynamics (CFD) software ANSYS® CFX® to simulate the removal of micropollutants from secondary effluents. Input data like reaction rate constants and initial concentrations of bulk components of the effluent organic matter (EfOM) were derived from experimental batch tests. Additionally, well-known correlations for the mass transfer were implemented into the simulation model. The CFD model was calibrated and validated by full-scale process data and by analytical measurements for micropollutants. The results show a good consistency of simulated values and measured data. Therewith, the validated CFD model described in this study proved to be suited for the application of secondary effluent ozonation. By implementing site-specific ozone exposition and the given reactor geometry the described CFD model can be easily adopted for similar applications. [ABSTRACT FROM AUTHOR]

Abstract: This paper numerically investigates four methods, namely mesh refinement, General Richardson Extrapolation (GRE), Grid Convergence Index (GCI), and the fitting method, in order to obtain a mesh independent solution for a straight blade vertical axis wind turbine (SB-VAWT) power curve using computational fluid dynamics (CFD). The solution is produced by employing the 2D Unsteady Navier–Stokes equations (URANS) with two turbulence models (Shear Stress Transport (SST) Transitional and ReNormalized Groups (RNG) κ − ɛ models). The commonly applied mesh refinement is found to be computationally expensive and not often practical even for a full 2D model of the turbine. The mesh independent power coefficient produced using the General Richardson Extrapolation method is found to be encouraging. However, the Grid Convergence Index may not be applicable in mesh independency tests due to the oscillatory behaviour of the convergence for the turbine power coefficient. As an alternative, the fitting method shows a good potential for the predicting of the mesh independent power coefficient without the necessity to consider a massive number of meshes. [Copyright &y& Elsevier]

The height of vertical sand filters are limited due to their structural cost. A horizontal sand filtermay offer a better alternative; however, flowchannels to the least resistance zone generated at the top of the filter as the sand gets wet and settles. A horizontal sand filter, internally baffled with spiral protrusion, is numericallymodelled to study the effect of these spirals in reducing the channelling and enhancing the filter's effectiveness. Three different spiral pitches, 1.0, 0.75, and 0.5 mhave been numerically modelled using Ansys FLUENT software. The parameters investigated were the power needed to run a flow rate through the horizontal filter and the residence time. The results show that as the spiral pitch decreases, the channelling reduces while the power increases. The power needed to pump a given flow rate of water in a 10 m long horizontal filter in all three cases investigated was less than the power needed to pump the same flow rate to the top of a 10 m long vertically standing sand filter. Results also showed that the time required for the flow to traverse through the sand filter increases in a nonlinear fashion as the pitch size decreases; however, the effectiveness of the filter increases. [ABSTRACT FROM AUTHOR]

This study is the first in a series dedicated to investigating the airflow and thermal management of electrical machines. Owing to the temperature dependent resistive losses in the machine's windings, any improvement in cooling provides a direct reduction in losses and an increase in efficiency. This study focuses on the airflow which is intrinsically linked to the thermal behaviour of the machine as well as the windage power consumed to drive the air through the machine. A full computational fluid dynamics (CFD) model has been used to analyse the airflow around all major components of the machine. Results have been experimentally validated and investigated. At synchronous speed the experimentally tested mass flow rate and windage torque were under predicted by 4% and 7%, respectively, by the CFD. A break‐down of torque by component shows that the fan consumes approximately 87% of the windage torque. [ABSTRACT FROM AUTHOR]

The effect of tree foliage on sprayer airflow through pear trees in a fruit orchard was studied and modelled in detail. A new three-dimensional (3-D) computational fluid dynamics model that integrates the 3-D canopy architecture with a local closure model to simulate the effect of the stem and branches and leaves of trees separately on airflow was developed. The model was validated with field observations made in an experimental orchard (pcfruit, Sint-Truiden, Belgium) in spring and summer 2008 and was used to investigate the airflow from three air-assisted orchard sprayers (Condor V, Duoprop and AirJet quatt). Velocity magnitudes were measured before and behind leafless and fully-leafed pear canopies across the row while the operating sprayers are passing along the row, and were compared with the simulations. The simulation results predicted the measured values well with all the local relative errors within 20%. The effect of foliar density on airflow from the three air assisted sprayers was manifested by changing the magnitude and direction of the sprayers' air velocity behind the canopy, especially at the denser regions of the canopy and by changing the pattern of velocity decay horizontally along the jet. The developed methodology will also allow a thorough investigation of atmospheric airflow in canopy structures. [ABSTRACT FROM AUTHOR]

The temperature distribution in polymer electrolyte membrane fuel cells (PEMFCs) plays a vital role in defining the overall efficiency and in ensuring the delivery of optimum performance, and understanding the heat transfer taking place is essential for the design of effective thermal and water management systems. This article describes a simple model, validated against experiment, which can be used to investigate the factors such as bipolar plate design, materials of construction, and the external effects of forced convection such as cooling fans and natural convection. The model employs computational fluid dynamics to account for the reactant flows in composite graphite plates and heat distribution within the stack, while convective heat transfer from the external surface of the fuel cell is treated using well-known heat transfer correlations. The computational model was validated using a novel fuel cell analogue composed of an electrically controlled heating plate to simulate the heat generated by the membrane electrode assembly and instrumented with 14 calibrated thermocouples. The model showed good agreement with the experiment over a wide range of gas flowrates, both in terms of local temperature distribution and overall energy balance. This suggests that the novel experimental methodology reported here could be used to support the design of bipolar plates for optimum heat transfer. [ABSTRACT FROM AUTHOR]

Turbulent mixing induces variability in concentration that is important in many applications, such as reactive plumes, risk assessments or odour impact analyses (when the effects can have time scales on the order of a second). In urban canopies, the variability may be modified by the presence of buildings. Our purpose is to study concentration fluctuation variance in built-up areas using an Eulerian approach. We performed numerical simulations with the computational fluid dynamics model Mercure_Saturne, which is a three-dimensional model adapted to atmospheric flow and pollutant dispersion. We use a k − ϵ turbulence closure and predict the concentration variance with a transport equation model. The model performance is evaluated with the near-full scale experiment MUST (Mock Urban Setting Test), a field experiment conducted in Utah’s West Desert Test Center. The modelled root-mean-square of the concentration fluctuations is compared to measurements for 20 of the MUST trials. The model shows good agreement with the measurements, with the fraction of predictions within a factor of two of observations of 60.1%, with better results for horizontal lines of detectors than for the detectors on vertical masts (with fractions of predictions within a factor of two of observations of respectively 66.4% and 52.6%). The influence of different parameters on the fluctuation variance is also studied and we show the importance of taking into account the stability of the stratification when modelling the turbulent kinetic energy. [ABSTRACT FROM AUTHOR]

In order to estimate the impacts of buildings on air pollution dispersion, numerical simulations are performed over an idealized urban area, modelled as regular rows of large rectangular obstacles. The simulations are evaluated with the results of the Mock Urban Setting Test (MUST), which is a near full-scale experiment conducted in Utah’s West Desert area: it consists of releases of a neutral gas in a field of regularly spaced shipping containers. The numerical simulations are performed with the model Mercure_Saturne, which is a three-dimensional computational fluid dynamics code adapted to atmospheric flow and dispersion simulations. It resolves complex geometries and uses, in this study, a k– ∈ closure for the turbulence model. Sensitivity studies focus on how to prescribe the inflow conditions for turbulent kinetic energy. Furthermore, different sets of coefficients available in the literature for the k– ∈ closure model are tested. Twenty MUST trials with different meteorological conditions are simulated and detailed analyses are performed for both the dynamical variables and average concentration. Our results show overall good agreement according to statistical comparison parameters, with a fraction of predictions for average concentration within a factor of two of observations of 67.1%. The set of simulations offers several inflow wind directions and allows us to emphasize the impact of elongated buildings, which create a deflection of the plume centerline relative to the upstream wind direction. [ABSTRACT FROM AUTHOR]

Concentration polarization is one of the main challenges of membrane-based processes such as power generation by reverse electrodialysis. Spacers in the compartments can enhance mass transfer by reducing concentration polarization. Active spacers increase the available membrane surface area, thus avoiding the shadow effect introduced by inactive spacers. Optimizing the spacer-filled channels is crucial for improving mass transfer while maintaining reasonable pressure losses. The main objective of this work was to develop a numerical model based upon the Navier–Stokes and Nernst–Planck equations in OpenFOAM, for detailed investigation of mass transfer efficiency and pressure drop. The model is utilized in different spacer-filled geometries for varying Reynolds numbers, spacer conductivity and fluid temperature. Triangular corrugations are found to be the optimum geometry, particularly at low flow velocities. Cylindrical corrugations are better at high flow velocities due to lower pressure drop. Enhanced mass transfer and lower pressure drop by elevating temperature is demonstrated. [ABSTRACT FROM AUTHOR]

Objectives: Repair of the right ventricular outflow tract (RVOT) in paediatric cardiac surgery remains challenging due to the high reoperation rate. Intimal hyperplasia and consequent arteriosclerosis is one of the most important limitation factors for graft durability. Since local shear stress and pressure are predictive elements for intimal hyperplasia and wall degeneration, we sought to determine in an oversized 12-mm RVOT model, with computed fluid dynamics simulation, the local haemodynamical factors that may explain intimal hyperplasia. This was done with the aim of identifying the optimal degree of oversizing for a 12-mm native RVOT., Methods: Twenty domestic pigs, with a weight of 24.6 ± 0.89 kg and a native RVOT diameter of 12 ± 1.7 mm, had valve conduits of 12, 16, 18 and 20 mm implanted. Pressure and flow were measured at 75, 100 and 125% of normal flow at RVOT at the pulmonary artery, pulmonary artery bifurcation and at the left and right pulmonary arteries. Three-dimensional computed fluid dynamics (CFD) simulation in all four geometries in all flow modalities was performed. Local shear stress and pressure conditions were investigated., Results: Corresponding to 75, 100 and 125% of steady-state flow, three inlet velocity profiles were obtained, 0.2, 0.29 and 0.36 m/s, respectively. At inflow velocity profiles, low shear stress areas, ranged from 0 to 2 Pa, combined with high-pressure areas ranging from 11.5 to 12.1 mmHg that were found at distal anastomosis, at bifurcation and at the ostia of the left and right pulmonary arteries in all geometries., Conclusions: In all three oversized geometries, the local reparation of shear stress and pressure in the 16-mm model showed a similar local profile as in the native 12 mm RVOT. According to these findings, we suggest oversizing the natural 12-mm RVOT by not more than 4 mm. The elements responsible for wall degeneration and intimal hyperplasia remain very similar to the conditions present in native RVOT., (© The Author 2015. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.)

Objectives: The reconstruction of the right ventricular outflow tract (RVOT) with valved conduits remains a challenge. The reoperation rate at 5 years can be as high as 25% and depends on age, type of conduit, conduit diameter and principal heart malformation. The aim of this study is to provide a bench model with computer fluid dynamics to analyse the haemodynamics of the RVOT, pulmonary artery, its bifurcation, and left and right pulmonary arteries that in the future may serve as a tool for analysis and prediction of outcome following RVOT reconstruction., Methods: Pressure, flow and diameter at the RVOT, pulmonary artery, bifurcation of the pulmonary artery, and left and right pulmonary arteries were measured in five normal pigs with a mean weight of 24.6 ± 0.89 kg. Data obtained were used for a 3D computer fluid-dynamics simulation of flow conditions, focusing on the pressure, flow and shear stress profile of the pulmonary trunk to the level of the left and right pulmonary arteries., Results: Three inlet steady flow profiles were obtained at 0.2, 0.29 and 0.36 m/s that correspond to the flow rates of 1.5, 2.0 and 2.5 l/min flow at the RVOT. The flow velocity profile was constant at the RVOT down to the bifurcation and decreased at the left and right pulmonary arteries. In all three inlet velocity profiles, low sheer stress and low-velocity areas were detected along the left wall of the pulmonary artery, at the pulmonary artery bifurcation and at the ostia of both pulmonary arteries., Conclusions: This computed fluid real-time model provides us with a realistic picture of fluid dynamics in the pulmonary tract area. Deep shear stress areas correspond to a turbulent flow profile that is a predictive factor for the development of vessel wall arteriosclerosis. We believe that this bench model may be a useful tool for further evaluation of RVOT pathology following surgical reconstructions., (© The Author 2014. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.)