Commercial Computational Fluid Dynamics Software Research Articles

Validation of Effectiveness Factor Correlations for Steam Methane Reforming in Ni-Based Washcoat Catalyst Layers Using Commercial Computational Fluid Dynamics Software

Validation of Effectiveness Factor Correlations for Steam Methane Reforming in Ni-Based Washcoat Catalyst Layers Using Commercial Computational Fluid Dynamics Software

Turbulent Particle Flow in Spent Nuclear Fuel Storage Systems

Deposition models are being developed with the commercial computational fluid dynamics software STAR-CCM+ to evaluate particulate deposition on spent nuclear fuel (SNF) canisters. The primary particulate of concern is chloride salts, which are dispersed in the atmosphere and then deposited onto the canisters. During dry storage, the primary degradation process is likely to be chloride-induced stress corrosion cracking (CISCC) at the heat-affected zones of the canister welds. It is known that stainless steel canisters are susceptible to CISCC; however, the rate of chloride deposition onto the canisters is poorly known, based on sparse field data from a small number of sites. This paper describes work looking at various approaches to modeling turbulence, such as Reynolds-averaged Navier Stokes (RANS) and large eddy simulation (LES), and its impact on particle flow and deposition within a ventilated SNF storage system. The deposition rate is determined for a vertical canister system and a horizontal canister system. LES has the potential to simulate turbulent flows more accurately versus RANS, but is much more computationally expensive. A k-omega version of the RANS turbulence model was used for this study. The computational efficient RANS steady-state model predicted a similar canister deposition result as the LES simulation for a vertical canister storage system. For a horizontal storage system, the RANS steady-state model predicted more particles depositing on the canister than the LES simulation, providing a conservative estimation for particle deposition. A wall correction factor was added to the RANS model to dampen the turbulence fluctuation normal to a surface that left undamped, leads to the RANS model overpredicting deposition along a surface for smaller particles. This work was done to further development of deposition models that could be used to plan and inform SNF canister aging management programs with predictive models for the timing and occurrence of canister CISCC. This work is part of a larger effort tasked with understanding the likelihood of canister degradation due to CISCC. These models are still under development, and testing is needed for validation. However, these models are being presented now to demonstrate to canister vendors, utilities, regulators, and stakeholders the value of this type of modeling.

Numerical Analysis of Altered Parallel Flow Heat Exchanger with Promoted Geometry at Multifarious Baffle Prolongs

This study investigated the influence of BFFSP on the thermohydraulic performance of a SATHEC(s) using a novel computational approach. The novelty lies in the detailed exploration of the interplay between BFFSP, MFRT, and key performance parameters. Unlike prior studies, which often focus on a limited range of operating conditions, this work employs a comprehensive parametric analysis encompassing two BFFSPs (95 mm and 125 mm) and four MFRTs (0.1, 0.3, 0.5, and 0.7 kg/h). This extensive analysis provides a deeper understanding of the trade-off between the HTRFR enhancement and PDP associated with the BFFSP across a wider range of operating conditions. This investigation leverages the power of computational fluid dynamics (CFD) simulations for high-fidelity analysis. ANSYS Fluent, a widely recognized commercial CFD software package, was used as a computational platform. A three-dimensional steady-state model of HEXR geometry was established. The cold fluid was modeled as water, and the hot fluid was modeled as water. The selection of appropriate turbulence models is crucial for accurate flow simulations within the complex geometry of HEXR. This study incorporates a well-established two-equation turbulence model to effectively capture turbulent flow behavior. The governing equations for mass, momentum, and energy conservation were solved numerically within the CFD framework. Convergence criteria were meticulously established to ensure the accuracy and reliability of the simulation results. BFFs are crucial components in HEXRs as they promote fluid mixing and turbulence on the HTRFR surface, thereby enhancing HTRFR. This study explores the interplay between BFFSP and HTRFR effectiveness. It is hypothesized that a larger BFFSP (125 mm) might lead to a higher HTC owing to the increased fluid mixing. However, the potential drawbacks of the increased PDP due to the flow restriction also need to be considered. The PDP across the HEXR is a critical parameter that affects pumping costs and overall system yield. This study investigates the impact of BFFSP on the PDP. It is expected that a larger BFFSP (125 mm) will result in a higher PDP, owing to the increased resistance to fluid flow. Here, we aim to quantify the trade-off between enhanced HTRFR and increased PDP associated with different BFFSPs. The optimal design of an HEXR seeks a balance between achieving a high HTRFR rate and minimizing pressure losses. HTRPD, a metric combining both HTC and PDP, was employed to evaluate the thermohydraulic performance. We hypothesized that a specific BFFSP might offer a superior HTRPD, indicating an optimal balance between HTRFR effectiveness and PDP for the investigated HEXR geometry and operating conditions. CFD simulations were conducted using ANSYS Fluent to analyze the effects of BFFSP and MFRT on the HTC, PDP, and HTRPD. The simulations employed a commercially available HEXR geometry with water as the cold and hot fluid. The results are presented and discussed to elucidate the relationships between the BFFSP, MFRT, and key performance parameters of the HEXR. This study provides valuable insights into the influence of BFFSP on the thermohydraulic performance of HEXRs. The findings can aid in optimizing the HEXR design by identifying the BFFSP that offers the best compromise between HTRFR enhancement and PDP for specific operating conditions. The results contribute to the knowledge base of HEXR design and optimization, potentially leading to improved yield in various industrial applications. The results indicate that a larger BFFSP (125 mm) leads to higher outlet temperatures but also results in a higher PDP compared to the 95 mm design. Conversely, the 95 mm BFFSP exhibits a lower PDP but achieves a lower HTC. In terms of thermohydraulic performance, as indicated by HTRPD, the 95 mm BFFSP with the lowest MFRT (0.1 kg/h) achieved the highest value, surpassing the 125 mm design by 19.81%. This suggests that a 95 mm BFFSP offers a better trade-off between HTRFR effectiveness and pressure loss, potentially improving the overall HEXR performance.

A computational fluid dynamics study of the influence of sleeper shape and ballast depth on ballast flight during passage of a simplified train

The paper assesses the effect on the air flow regime underneath a simplified high-speed train of changing the ballast depth and the sleeper shape, with regard to its potential for causing ballast flight or pickup. The study was carried out numerically using the commercial Computational Fluid Dynamics (CFD) software AnSys Fluent. The flow profile beneath the underbody of the train was generated by means of a moving wall above the track. The Delayed Detached Eddy Simulation (DDES) with the SST [Formula: see text] turbulence model was used to simulate turbulent flow, and the ballast bed roughness was applied parametrically using the wall roughness feature when resolving the boundary layer. CFD simulations were validated for flow over a cube, showing good agreement with experimental results. Up to three different depths to the ballast surface and three different sleeper profiles were investigated. Velocity profiles and aerodynamic forces on cubes placed between or on top of the sleeper blocks were used to assess the propensity of individual ballast grains for movement. For a standard G44 sleeper, increasing the ballast depth and/or the ballast bed roughness was found to reduce aerodynamic loads on an individual ballast grain. A ballast grain on top of the sleeper is more prone to uplift than a grain on the surface of the ballast bed in the crib. A curved upper surface to the sleeper is beneficial in that it prevents ballast from settling on top, the most vulnerable position. However, the reduced flow separation associated with the curved top may increase the likelihood of ballast pickup from the crib. Hence new sleeper shapes intended to reduce the potential for ballast flight should not only prevent ballast from settling on top, but also increase flow separation through the provision of a sharp surface. A prismatic sleeper shape that achieves both is suggested.

An In-Depth Comparison of Straight and Wavy Microchannel Heat Exchangers

Abstract This paper presents extensive fluid flow and Heat-Transfer studies conducted using a commercial computational fluid dynamics (CFD) package known as CFD-ACE® to elaborate and expand on the reference studies available for ceramic-compact counterflow microchannel heat exchangers (MCHEs). The computational 3D model was developed using an experimentally tested MCHE and validated with experimental data with 3–5% variation for hot fluid and 6–12% variation for cold fluid for the entire design of experiments (DoEs). This study aimed to identify the performance of novel microchannel shapes using numerical analysis. The MCHE has good heat exchange properties, a compact design at industrial throughput, and a lower inner volume. During the study and identification of novel channel shapes, the segmented wavy MCHE was evaluated. The results were compared with those of the same volume and area straight MCHE baseline design under various identical operating conditions. Although the performance in terms of effectiveness is increased up to ∼12–25% in wavy MCHE with respect to straight MCHE simultaneously, the pressure drop is also increased by ∼60–80% under the same operating conditions. Therefore, performance and trade-offs are required to make the correct decision regarding feasibility. The effectiveness of the heat-transfer enhancement was also evaluated by plotting the heat-transfer coefficient ratio with respect to the pressure ratio of the two designs under identical operating conditions. This numerical study clearly indicates that wavy channels are better from the thermal performance point of view, whereas straight channels are better from the pumping power point of view, and the quantitative values are presented in graphical form.

Hydrodynamic characteristics of wing-in-ground effect oscillating hydrofoil on power extraction performance

The energy contained in the tidal motion of the seas and oceans has the potential to be a significant source of renewable energy. The oscillating hydrofoil current-energy turbine has a good performance to extract energy from the coupling of its heaving and pitching motions. In the present study, the wing-in-ground (WIG) effect has been considered to improve the power-extraction performance of the oscillating hydrofoils. The overset grid in the commercial computational fluid dynamic (CFD) software STAR CCM+ is applied to study the flapping hydrofoil with dynamic WIG effect between two hydrofoils. The simulation results show that the WIG effect can greatly improve the power extraction performance of the flapping hydrofoil. The WIG effect is asymmetric over the course of the foil moving toward or leaving from the symmetry plane. The distance of the gap has a major influence on the hydrodynamic performances of the flapping hydrofoil. For a moderate gap, the positive pressure on the lower surface enhances as the hydrofoil departs from the symmetry plane and causes an improvement of lift and moment coefficients. As the gap decreases further, the increasing negative pressure between the leading edge and the symmetry plane plays an essential role improving the power extraction as the hydrofoil approaches the symmetry plane. Compared to the case without the WIG effect, the power-extraction efficiency has an increment of 16.34% in the present study.

Water Flow Boiling in Micro/Mini Channels Using Volume of Fluid Model

Recent advancements in computational fluid dynamics (CFD) have triggered research in the field of heat exchangers. Driven by the need to decrease the size of heat exchangers, many researchers have exploited the higher heat transfer achieved by replacing single-phase flow systems with boiling counterparts. The concept of using mini-channels to provide compact heat exchangers while maintaining heat transfer performance is relatively new. A minimal number of researchers have reported simulations of water-steam systems in mini-channels. This paper presents a numerical study of the heat transfer performance (HTP) of mini channels in a water-steam system using the volume of fluid (VOF) model coupled with the Lee phase change model on commercial CFD software ANSYS. The numerical model consisted of a 1 mm × 1.5 mm × 52 mm channel with boundary conditions: top adiabatic; constant heat flux at the bottom surface; left/right periodic; mass flow inlet and pressure outlet. A mesh independence study was carried out for the proposed model, and simulations were validated against the experimental results of heat transfer versus vapor quality for a wide range of mass and heat fluxes. The VOF model best predicts experimental HTC at high mass fluxes, although the results at low mass fluxes were predicted with reasonable accuracy. Based on the agreement of numerical and numerical results, the VOF model turned out to be a promising candidate for designing compact micro/mini channel heat exchangers.

CFD Study for Wave Run-up Characteristics Around a Truncated Cylinder with Damper

In this study, numerical simulations for a single fixed truncated circular cylinder in regular waves were conducted to investigate the nonlinear wave run-up under various dampers and wave period conditions. The present study used the volume of fluid (VOF) technique to capture the air-water interface. The unsteady Reynolds-averaged Navier–Stokes (URANS) equation with the k– ϵ turbulence model was solved using the commercial computational fluid dynamics (CFD) software STAR-CCM+. First, a systematic spatial convergence study was conducted to assess the performance and precision of the present numerical wave tank. The numerical scheme was validated by comparing the numerical results of wave run-up on a bare truncated cylinder with the experimental results, and a good agreement was achieved. Then, a series of parametric studies were carried out to examine the wave run-up time series around the truncated cylinder with single and dual dampers in terms of the first- and second-order harmonic and mean set-up components. Additionally, the local wave field and the flow velocity vectors adjacent to the cylinder were evaluated. It was confirmed that under short wave conditions, the high position of the damper led to a noticeable increase in the wave run-ups with significant changes in the first- and second-order harmonic components.

Investigation of Taylor bubble dynamics in annular conduits with counter-current flow

This study numerically investigates counter-current slug flow by considering the motion of a Taylor bubble in annular conduits with downward-flowing liquids using the Volume-of-Fluid method implemented in the commercial computational fluid dynamics software ANSYS Fluent (Release 19.2). The translational velocity of a counter-current ascending or co-current descending Taylor bubble in vertical concentric annuli and the corresponding distribution parameter (C0) are analyzed. The latter is correlated in terms of Eötvös number (Eo) and inverse viscosity number (Nf) within the range of Eo between 40 and 400 and Nf between 40 and 320. The proposed correlation provides an accurate fit to the numerical data with an average error of 2.64%, and is successfully compared with published numerical findings. In general, the smooth and stable shape of the bubble is disrupted as the counter-current flow velocity (Frl) increases above a critical value, leading to the formation of surface waves and the displacement of the bubble tip away from the annular gap center and towards the outer pipe. C0 increases with Eo and Nf, plateauing at high values of Eo. The effects of annulus inclination (θ) and eccentricity (ε) on bubble rise velocity are examined within the common range of θ and ε encountered during the drilling of oil, gas, or geothermal wells, i.e. 0° ≤ θ ≤ 60° and 0 ≤ ε ≤ 0.7, and their impact on the C0. The increasing Frl and θ lead to a streamlined bubble with pointed nose and thus a reduction in the wrap angle (θwrap), ultimately leading to reduced drag compared to the vertical annulus case and a decrease in C0. As the ε increases, which is accompanied by an increase in the degree of bubble eccentricity, the corresponding C0 decreases. For a constant Eo = 100 and Nf = 160 with inclination angle of θ = 40°and eccentricity of ε = 0.5, the C0 < 1 is observed.

Neutronic-coupled thermal hydraulic analysis of flow blockage in the hottest wire-wrapped LBE-cooled fuel assembly

Flow blockage in lead-cooled fast reactors is considered a realistic accident for fuel assemblies, whereas reactivity feedback and axial power profiles are considered in few studies due to the complexity and lack of neutronic modules in commercial computational fluid dynamic software. This study proposes a neutronic-coupled thermal–hydraulic model to analyze the coupling effect on flow blockage in a 19-pin wire-wrapped fuel assembly. Neutronic and thermal hydraulics were validated by comparing the reported benchmark and experimental data, respectively. Simulation results with and without neutronic coupling schemes were compared, and case studies of different reactivity insertions were conducted. The wall overheating of blockages with coupling schemes is more conservative than the constant heat source condition with the lower dimensionless temperature T¯. After a step change of cross-section, the response of Rw and T¯ shows synchronous behavior. For a larger reactivity insertion, it leads to higher wall heat flux, lower wall thermal resistance and lower dimensionless temperature for blockage regions.

Enhancing indoor air quality and thermal comfort in indoor swimming pool facilities: investigating the impact of ventilation system configurations

This study focuses on enhancing indoor air quality and thermal comfort in indoor swimming pool facilities through the investigation of ventilation system configurations. Creating a comfortable and healthy environment in these facilities is crucial for the well-being of occupants and overall operational efficiency. The performance of the ventilation system significantly influences user comfort, energy consumption, and air quality. This research aims to analyze the impact of different ventilation system configurations on indoor air quality and thermal comfort parameters using computational fluid dynamics (CFD) simulations.To achieve the research objectives, CFD simulations were conducted using ANSYS Fluent ®, a widely used commercial CFD package. The simulations involved solving the governing equations for continuity, momentum, energy, and species transport, along with employing the k-epsilon turbulence closure model. A high-resolution mesh with over 5.6 million elements accurately captured the flow regimes and related phenomena.The study investigated various aspects of ventilation system configurations, including the placement and design of inlets and outlets, airflow rates, and distribution patterns. Evaluations were made based on key performance indicators such as indoor air quality parameters, thermal comfort indices, and energy efficiency metrics. Comparisons were made between different configurations to identify the most effective strategies for enhancing indoor air quality and thermal comfort.The findings of the study demonstrate the importance of ventilation system design in achieving optimal indoor air quality and thermal comfort in indoor swimming pool facilities. The results indicate that specific configuration choices, such as the use of circular inlets in the ceiling for improved spectator comfort and rectangular inlets in the side walls for better performance in the swimming pool area, can significantly impact thermal conditions and air distribution. Additionally, the study emphasizes the need for appropriate inlet grille height to ensure adequate air mixing and thermal comfort.The outcomes of this research provide valuable insights for architects, engineers, and facility managers involved in the design, construction, and operation of indoor swimming pool facilities. By understanding the impact of different ventilation system configurations, stakeholders can make informed decisions to optimize indoor air quality, thermal comfort, and energy efficiency. Ultimately, this research contributes to the development of sustainable and comfortable indoor swimming pool environments that cater to the needs of occupants and enhance their overall experience.

A numerical study of the settling of non-spherical particles in quiescent water

Settling of non-spherical particles is poorly understood with previous studies having focused mainly on spherical particles. Here, a series of particle-resolved direct numerical simulations are conducted using FLOW-3D (commercial computational fluid dynamics software) for spheres and five regular, non-spherical shapes of sediment particles, i.e., prolate spheroid, oblate spheroid, cylinder, disk, and cube. The Galileo number varies from 0.248 to 360, and the particle Reynolds number Rep ranges from 0.002 77 to 562. The results show that a non-spherical particle may experience larger drag and, consequently, attain a lower terminal velocity than an equivalent sphere. If Rep is sufficiently small, the terminal velocity is less affected by particle shape as characterized by the particle aspect ratio. For relatively large Rep, the shape effect (represented by the Corey shape factor) becomes more significant. Empirical correlations are derived for the dimensionless characteristic time t95∗ and displacement s95∗ of particle settling, which show that t95∗ remains constant in the Stokes regime (Rep &amp;lt; 1) and decreases with increasing Rep in the intermediate regime (1 ≤ Rep &amp;lt; 103), whereas s95∗ increases progressively with increasing Rep over the simulated range. It is also found that in the Stokes regime, particle orientation remains essentially unchanged during settling, and so the terminal velocity is governed by the initial orientation. In the intermediate regime, a particle provisionally settling at an unstable orientation self-readjusts to a stable equilibrium state, such that the effect of initial orientation on the terminal velocity is negligible. Moreover, an unstable initial orientation can enhance the vertical displacement and may promote vortex shedding.

Parametric Reduced-Order Modeling of Battery Thermal Management Systems for Varying Rates of Cooling Liquid Flow

The thermal management system in battery packs for electrical/hybrid electric vehicles plays an important role in maintaining good performance and health of battery cells. In order to optimize the thermal management system design, computational fluid dynamics (CFD) simulations are often used. The CFD is a powerful tool that can accurately simulate the thermal behavior of the system using numerical computation techniques such as finite volume method. However, the days-long computational expense means that the CFD-based simulations are still unsuitable for situations when rapid results are required, for example for online predictive control or fast-pace optimization design.A new method of reduced-order modeling of battery thermal management systems (BTMS) was presented in [1]. Given a CFD model, the algorithm based on projection on Krylov-subspace yields a reduced-order model (ROM). The ROM accurately predicts the system’s transient response to arbitrary internal heating of individual batteries and temperature of cooling liquid at inlet. Unlike conventional Krylov-subspace approaches, the algorithm does not require the system matrix of the CFD model. Therefore, the method is more suitable for use with commercial CFD software which does not allow access to such internal information. The ROM uses a drastically reduced number of degrees of freedom requiring drastically reduced simulation time.This paper extends our ROM by including the mass flow rate of cooling liquid as a model parameter. The task is accomplished by interpolating the system matrices after several local reduced-order models are constructed at discrete mass flow rates (MFR). In order to interpolate the local ROMs, we first need to transform the local ROMs onto a common subspace. The transformation matrix is obtained by applying the singular value decomposition (SVD) to the local projection matrices. In this paper, three local ROMs are built at 3 different MFRs. After these local ROMs are transformed according to the above procedure, a parametric reduced-order model (pROM) is constructed via quadratic interpolation.The constructed pROM is tested against the new MFRs different from those used for building the local ROMs. For each new MFR, the pROM produced a transient response that is almost indistinguishable from that of the CFD model (e.g., see Figure 1). The several thousand core-hour computational time needed for CFD simulations is replaced by a few tens of seconds using the pROM on a personal computer. The low computing load of the pROM is deemed adequate for on-board applications. Reference [1] Xiang L, Lee CW, Zikanov O, Hsu C-C. Efficient reduced order model for heat transfer in a battery pack of an electric vehicle. Applied Thermal Engineering. 2022; 201:117641.Figure 1 Figure 1

Structural Reliability Analysis of Large Planar Steam Solid Oxide Electrolysis Cells

Solid oxide electrolysis cells (SOEC) have been receiving significant attention recently because of their high energy efficiency and fast hydrogen production. In our previous study, a multi-physics modeling framework to simulate the SOEC performance and structural reliability of planar SOEC design was developed and demonstrated. The electrochemical reactions, fluid dynamics, species transport, electron transfer, and heat transfer were modeled in the commercial computational fluid dynamics (CFD) software STAR-CCM+. The thermomechanical analysis and the associated structural reliability evaluations were conducted using the commercial finite element analysis software ANSYS. The electrochemistry model was validated by using the experimentally obtained current-voltage (I-V) characteristics of the electrode-supported SOECs. In this study, this framework was applied on a large 300 cm2 steam planar SOEC design, and systematically studied the structural reliability under combinations of cell operating conditions, with cell voltage 1-1.5 V, steam fraction in fuel inlet 0.7-0.9, air inlet flow rate 0-10 L/min, fuel inlet flow rate 2.5-12.5 L/min, and inlet temperature 600-900 C. In the modeling framework, all the cells were investigated under the adiabatic thermal conditions, which is equivalent to packing the cell in an insulated container. This induced the relatively larger temperature variation than in the smaller cell designs. This cell internal temperature non-uniformity may further enhance the spatial variations of open circuit voltage, activation loss, and ionic conductivity in the cell, which all influence the overall cell performance. This situation is more obvious when the cell voltage is higher than 1.35V, under which the cell is significantly heated along the steam flow direction. Traditionally, it is assumed that the cell internal temperature spatial variation plays an important role on cell structural reliability. However, because it was assumed that all the components in cell are stress free at 850 , the cell temperature deviation from 850 is more critical to the stress distribution and structural reliability in the cell. For the investigated cells in the practical conditions, like 750 C inlet temperature and varying voltage from 1.05 to 1.5 V, the highest first principal stress is always in the air side electrode, which is around 45 MPa. This is explained by the higher coefficient of thermal expansion of LSCF-GDC with respect to the other layers. This may indicate that the failure would possibly occur in the air side electrode, but at low risk due to the relatively higher Weibull characteristic strength.

A numerical approach to investigate the effect of various fluids on the performance of a heat pipe

The present study is carried out using CFX, a commercial computational fluid dynamics (CFD) software, to estimate the thermal characteristics of a heat pipe. A heat pipe consists of three concentric circular tubes with three different split sections: Evaporator, adiabatic, and condenser sections. A detailed parametric study takes water and methanol as working fluids – Additionally, a study investigates the heat pipe with condenser section subjected to ambient air. The complete analysis is performed for an existing heat pipe with given design characteristics such as orientation, diameter and length, wick structure, and the stated circumstances and intake flow to the evaporator. The results are reported and compared in graphical form. It is observed that the water improves the heat pipe thermal features in terms of temperature than that of methanol. The maximum surface temperature is recorded in the evaporator zone at 132 oC, while the lowest temperature was measured at the conclusion of the condenser portion at 87.6 oC. The condenser portion's extreme surface temperature is 79.93 oC, whereas the evaporator portion's extreme surface temperature is 127 oC. When attributes are compared at atmospheric pressure, water outperforms methanol in terms of merit. This shows that compared to methanol, water has greater heat transfer properties.

Improving the power output estimation for a tidal power plant: a case study

The aim of this study is to analyse the importance of considering the variation in the discharge coefficient (Cd) of a sluice passage and the tidal current speed (i.e. the flow speed approaching the passage) in improving the estimation of power output for a tidal power plant. The simulation results, using a commercial computational fluid dynamics software package, Flow 3D, have shown that the Cd value of a sluice passage varies with the upstream (i.e. on the sea side of the impounded area) water level. In addition, the results of a case study carried out in the Taedong bay (Democratic People's Republic of Korea), using a zero-dimensional model, highlight the importance of considering variations in the tidal current speed as well as Cd when estimating the power output for a tidal power plant. In this study, a detailed scheme is proposed to consider the approach speed at each stage of filling, holding, generating and holding for the mode of ebb generation. It is hoped that the results of this study will help scientists, engineers and decision makers to accurately evaluate the tidal power output of tidal barrages and lagoons in many regions of the world.

Improving performance of H-Type NACA 0021 Darrieus rotor using leading-edge stationary/rotating microcylinders: Numerical studies

In the current paper, a computational study has been performed to simulate a novel concept in which a fixed/rotating microcylinder is installed upstream of the leading edge of the NACA 0021 airfoil, aiming to enhance the performance of the H-type Darrieus rotor. The idea behind implementing a fixed/rotating microcylinder is to enhance the lift to drag ratio due to increasing near-wall momentum through generated vortices transferring the momentum from the outer flow to the near-wall flow region of the airfoil. Parametric analyses for the microcylinder including its location, size, shape (circular, square and rhombus), and rotation were performed. The commercial Computational Fluid Dynamics (CFD) package ANSYS Fluent was used for solving the Unsteady Reynolds Averaged Navier-Stokes (URANS), and turbulence equations. The code has been based on Finite Volume Method (FVM) with the pressure-based solver developed for low-speed incompressible flows. The semi-implicit method for pressure-linked equation (SIMPLE) was used to solve the discretized equations. The URANS was used with adopting the SST k-ω turbulence model to find out the optimum rotor by utilizing the microcylinder model. An optimization methodology using Response Surface Optimization (RSM) based on Kriging method has been first performed to find the optimum size and location of a circular microcylinder. The optimization study indicated an optimum microcylinder diameter (d/C = 0.0085313), at an upstream chordwise distance and normal to it 0.070275 and 0.02303 of the chord length (C), respectively. The results showed also that a small static circular microcylinder of d/C = 0.009 and installed at 0.075C from the leading edge (MC5) is an efficient geometry at high regime of tip-speed ratios (TSR≥2.2) rather than lower regime of TSRs. When these superior set of rotating (5 rad/s) microcylinder (MC5) parameters were adopted, significant enhancement of power coefficient (Cp) could be achieved and a considerable improvement of the maximum power coefficient (Cpmax) up to 120 % at TSR = 3 appeared. A physical analysis of the flow fields using the contours of vorticity, pressure and turbulence energy has been performed to illustrate the effect of rotating microcylinder for improving rotor performance. The vorticity contours showed the ability of rotating microcylinder for generating a strong vortex structure in its wake for enhancing turbulence production around the blades, which delayed the known strong stall of the blades by diminishing the separation bubble size. This generally improved the blades aerodynamic performance and enhancing the lift-to-drag ratio.

Experiment and Numerical Studies of the Effect of Equivalent Ratio on Combustion Characteristics in Fluidized Bed Gasifier

The effect of equivalent ratio on fluidized bed gasifier on using kernel mixed palm cake as feedstock was studied experimentally and numerically. A 3-D numerical model of the reactor, similar to the experimental setup, was created using the commercial computational fluid dynamics (CFD) software ANSYS 2019 (Fluent). The fuel feed rate was fixed at 3 kg/hour and the mass flow rate of the air was varied, setting it to equivalent ratios (ER) of 0.1, 0.3, 0.5, and 0.7. The axial temperature profile in the reactor was compared between experimental measurements and numerical simulations and a good agreement was found. Carbon monoxide and volatiles increased when the equivalent ratio decreased, according to the simulations. It was found that ER = 0.1 and ER = 0.3 are suitable equivalent ratios, although the former would not give continuous combustion due to too low reactor temperature.

Performance Optimization Of A Microfluidic Virus Detection Cartridge: A Numerical And Experimental Study.

Detection and imaging of viruses in a complex solution is particularly significant for virology and requires a comprehensive understanding of biosensors. While lab-on-a-chip systems are used in virus detection as biosensors, analysis and optimization of these systems are especially challenging due to the size of the system to be used in the certain application. The system of interest for virus detection is required to be cost efficient and is also needed to be able to easily operable with a simple setup. Moreover, the detailed analysis of these microfluidic systems should be made with precision in order to predict the capabilities and the efficiency of the system accurately. This paper reports on the use of a common commercial computational fluid dynamics (CFD) software for the analysis of a microfluidic lab-on-a-chip virus detection cartridge. This study evaluates the problems commonly encountered during microfluidic applications of CFD softwares particularly in the area of reaction modeling of the antigen-antibody interaction. CFD analysis is later validated and combined with experiments to optimize the amount of dilute solution used in the tests. Thereafter, the geometry of the microchannel is also optimized and optimal test conditions are set for a cost efficient and effective virus detection kit using light microscopy.

Numerical investigation of the effect of carotid bifurcation stenosis degree on pulsatility characteristics.

Arterial bifurcations are regions that are susceptible to hemodynamic effects and thrombus formation. In the current study, the hemodynamic effects of a simplified 3D model of an arterial bifurcation were simulated using the commercial computational fluid dynamics software FLUENT. The non-Newtonian properties of blood were modeled using the Carreau model, and the pulsation dynamics and heat transfer characteristics of blood at different degrees of stenosis in the arterial bifurcation were analyzed. The results indicate that arterial stenosis caused by a thrombus when the pulsation velocity reaches its peak has an essential impact on blood transport. The stenosis of the bifurcation increases the peak pulsatile flow pressure drop, and each 0.5mm stenosis of the arterial bifurcation increases the mean wall shear stress of the bifurcated segment by approximately 0.25Pa. From the heat transfer perspective, arterial stenosis has little effect on the heat transfer coefficient. The heat transfer coefficient measured inside the bifurcation is much larger than that measured outside the bifurcation. The stenosis of the arterial bifurcation causes an increase in the mean velocity of the arterial cross-section, and the volume-averaged absolute vorticity is introduced to quantify the secondary flow effect during the pulsation cycle, where the arterial stenosis causes an increase in the mean absolute vorticity at pulsation velocity and accelerates the decay of the vorticity at uniform velocity. In this paper, the hemodynamics of carotid bifurcation pulsation is analyzed in conjunction with flow field properties to reveal the flow field dynamics factors and heat transfer characteristics of local stenosis of the carotid bifurcation and to conduct an exploratory study for the diagnosis and treatment of carotid bifurcation thrombosis.