CFD Program Research Articles

Mathematical Models for Removal of Pharmaceutical Pollutants in Rehabilitated Treatment Plants

This paper aims to investigate appropriate mathematical models devoted to the optimization of some cleaning processes related to pharmaceutical contaminant removal. In our recent works, we found the rehabilitation of the existing cleaning plants as a viable solution for the removal of this type of micropollutants from waters by introducing efficient techniques such as adsorption on granulated active carbon filters and micro-, nano-, or ultrafiltration. To have these processes under better control and to assure the transfer from small- to large-scale treatment stations, specific mathematical models are necessary. Starting from Navier–Stokes equations and imposing proper boundary conditions, some mathematical physics problems are obtained for which adequate solving methods via variational methods and surjectivity results are proposed. The importance of these solution characterizations consists in their continuation in adequate numerical methods and the possibility to visualize the result by using a CFD program.

Investigations of inlet arrangement strategies and particle parameters on thermochemical performance in falling particle solar reactors

The reformation of methane to hydrogen and steam in a falling particle solar reactor (FPSR) is a promising method to use the solar energy, which converts solar energy into chemical energy. FPSR has higher operation temperature, higher pressure bearing capacity and more direct heat energy storage than those of traditional reactor. However, due to the short residence time of the particles, hydrogen production efficiency is reduced. Thus, inlet arrangement strategies and particle catalysts should be carefully designed to improve the thermochemical reaction performance of FPSR. In this contribution, the Eulerian-Eulerian model in CFD program (Fluent 2020 R2) is used to explore the effects of different particle inlet arrangement strategies, non-uniform particle mass flow inlet and particle size on the performance enhancement of methane steam reforming reaction. The results indicate that the two arrangement strategies show different trends in influencing hydrogen production efficiency. Besides, non-uniform particle mass flow rate also has a significant impact on hydrogen production efficiency, with the optimal arrangement conditions increasing the hydrogen production rate by 2.4831 mol/m−3(−|-) s−1. Additionally, smaller particle size demonstrates better hydrogen production efficiency, with a 0.15 mm particle size catalyst showing a 14.02 % improvement in hydrogen production efficiency compared to a 0.75 mm particle size. This contribution can provide a guidance for optimizing the heat and mass transfer performance of the falling particle solar reactor.

Modeling and Visualization of Coolant Flow in a Fuel Rod Bundle of a Small Modular Reactor

This article presents the results of an experimental study of the coolant flow in a fuel rod bundle of a nuclear reactor fuel assembly of a small modular reactor for a small ground-based nuclear power plant. The aim of the work is to experimentally determine the hydrodynamic characteristics of the coolant flow in a fuel rod bundle of a fuel assembly. For this purpose, experimental studies were conducted in an aerodynamic model that included simulators of fuel elements, burnable absorber rods, spacer grids, a central displacer, and stiffening corners. During the experiments, the water coolant flow was modeled using airflow based on the theory of hydrodynamic similarity. The studies were conducted using the pneumometric method and the contrast agent injection method. The flow structure was visualized by contour plots of axial and tangential velocity, as well as the distribution of the contrast agent. During the experiments, the features of the axial flow were identified, and the structure of the cross-flows of the coolant was determined. The database obtained during the experiments can be used to validate CFD programs, refine the methods of thermal-hydraulic calculation of nuclear reactor cores, and also to justify the design of fuel assemblies.

Numerical Analysis of a Self-Acting Gas Bearing Lubricated with a Low-Boiling-Point Medium Using an Advanced Model Based on the Finite Difference Methods and Universal Computational Fluid Dynamics Software

Methods for determining the characteristics of self-acting (aerodynamic) gas bearings have been developed for many years, but many researchers and engineers still question how sophisticated a model of such bearings should be to obtain reliable results. This is the subject of this article, which presents a numerical analysis of aerodynamic gas bearings using two alternative methods: a specialized program based on the finite difference method, and a universal CFD program using the finite volume method. Gas bearings with a nominal diameter of 49 mm, designed for a 10 kW turbogenerator operating at a rotational speed of 40,000 rpm, are analyzed. The vapor of the low-boiling medium, designated HFE-7100, is used as the bearing lubricant. The calculations focus on determining the position of the bearing journal where the bearing achieved the required load capacity and checking the bearing characteristics beyond the nominal operating point. The most important results obtained by the two independent methods are compared, and recommendations are made for those interested in the numerical analysis of self-acting gas bearings.

The effect of lateral intake slope on sedimentation transport

Generally, The problem of sediments at the entrances to subsidiary channels is considered one of the most common problems for which water resources engineers seek to find appropriate solutions, as it causes significant damage to hydraulic installations, as the accumulation of these sediments in the canal rollers over time leads to the collapse of those channels, which results in many losses. In this study, a three-dimensional mathematical model was developed using the Ansys Fluent CFD program, and this model was matched with previous laboratory experiments, as this mathematical model showed clear accuracy and consistency. Work was done on changing the geometry of the sub-channel and studying the effect of changing the inclination of the sub-channel on reducing the amount of sediment entering the channel or not, since the channel used in this study is 2 m. Adjustments were made to the inclination of the canal in two different forms: The first is to make the first half (1 m) of the canal horizontal, and the inclination begins in the second half, at three different angles, namely 15, 30, and 45 degrees. The other form is to change the inclination along the total length of the sub-channel (2 m) with the same effect. Angles 15, 30 and 45. The results showed the ineffectiveness of changing the inclination of the sub-channel from the middle of the distance, while the results of changing the total inclination were different. It is possible that the slope angle of 45 is considered the best in terms of increasing the speed and clearly reducing the area of the separation zone and the erosion zone.

Verification and validation of a coupled CFD–FEM approach with overset structured grid through free decay and regular wave tests

This paper presents a comprehensive verification and validation study applied to the hydrodynamic analysis of a semi-submersible Floating Offshore Wind Turbine (FOWT) platform. The numerical simulation is conducted using a coupled Computational Fluid Dynamics-Finite Element Method (CFD–FEM) approach. The CFD program incorporates an overset grid interpolation method, facilitating a more systematic grid refinement in the estimation of discretization uncertainties. A mooring analysis program, based on the FEM scheme, is integrated with the CFD program to simulate the dynamic responses of mooring system. The necessity of the nonlinear mooring model is demonstrated by comparing solutions with a comparative test using a linear mooring model. The verification study, based on a least-squares-based extrapolation method, quantifies the spatial and temporal discretization errors of the numerical model. The numerical solutions based on the baseline model are further validated against the model test measurements. A pitch free decay model test and a regular wave model test conducted within the OC5 project are utilized for the verification and validation study. Results from both tests demonstrate the reliability and accuracy of the coupled method.

Hydrothermal analysis for a slinky-type horizontal borehole heat exchanger equipped with turbulator considering various ground depths

This work critically evaluates hydrothermal behavior inside the slinky-type horizontal borehole heat exchanger with turbulator. The employed turbulator is the spiral twisted tape. The simulations are performed using the finite volume approach in the laminar flow area (Re = 250–400) using a commercial CFD program. Four ground depths (600, 1000, 1400, and 1800 mm) are selected for the proposed heat exchangers, and the outcomes are compared with and without the proposed turbulator. The obtained numerical results demonstrate that in all of the proposed situations, the average Nussel number and heat transfer coefficient grow as the Reynolds number increases. For a given Reynolds number, increasing the depth of the proposed borehole heat exchanger results in a greater heat transfer coefficient. Also, the turbulator-equipped model's outlet temperature values are higher than those of the non-turbulator-equipped model due to the presence of spiral twisted tape. More swirl flows result from this, which speeds up the rate at which heat is transferred from the fluid inside the proposed heat exchanger to the nearby soil. Moreover, the pressure drop increases as the Reynolds number augments, and this tendency is the same for both cases with and without turbulators. Furthermore, the model with 1000 mm depth at Re = 350 has the best thermal performance, and the model with 1400 mm depth is in the second level at Re = 350. The model with 1800 mm depth is attributed to having the lowest thermal performance in all analyzed Reynolds numbers because of the model's more considerable pressure drop. The model with a depth of 1800 mm has the lowest thermal performance at the lowest value of the researched Reynolds number (Re = 250). The models, including 600, 1000, and 1400 mm depths, have thermal performances of approximately 23.53, 11.76, and 8.82 % higher, respectively, than the reference model (1800 mm depth). According to the lowest Reynolds number trends, the model with a depth of 1800 mm has the lowest thermal performance at Re = 400, the maximum value of the analyzed Reynolds number in this case. Compared to the reference model (1800 mm depth), the thermal performance of the other models—including those with 600, 1400, and 1000 mm depths—is roughly 6.67, 11.11, and 26.67 % greater, respectively.

Numerical study on the condensation characteristics of vapor with non-condensable gas on inclined walls inside containment

In the Westinghouse AP series steel containment vessel, the outer wall is cooled by spray and natural convection, while the internal vapor is allowed to condense on the inner wall. At this point, the containment dome becomes part of the condenser wall, and its curved structure can change the flow mode of the condensate water, thereby affecting the local condensation (heat exchange) capability of the wall. This article is based on the CFD program FLUENT and develops a UDF program suitable for the condensation of vapor with non-condensable gas. The influence of the wall tilt angle on the condensation characteristics of vapor with non-condensable gas is investigated and compared with experimental data from Xi'an Jiaotong University. The results show that the numerical simulation is in good agreement with the experimental results.

Flame Deflector Modification for Improved Combustion Efficiency in Domestic Gas Ovens

ABSTRACT This research aimed to examine the effect of port placements in the flame deflector on the combustion efficiency of the grill burner within a domestic gas oven. Six different configurations of the flame deflector were designed for this purpose. Emission tests of the grill burner were carried out at two different pressures for 1 h according to EN30 standard for all types of flame deflectors. The reduction in the C O N content by %11.3 was observed in the flame deflector of No_6 as compared to default deflector. The CFD analysis of the No_6 flame deflector was also carried out to examine the air flow pattern of the flame deflector through the grill burner. Results showed that the air flow from the flame deflector into the grill burner was more uniform than that of the default flame deflector. The temperature, the mass fraction of fuel/air, and CO and CO2 distribution in the grill burner through combustion process were numerically simulated using commercial CFD program, FloEFD. The most appropriate chimney position was recommended based on the distribution of CO2 content. Emission tests and efficiency tests of two different chimney prototypes with different chimney areas (1260 mm2 and 1400 mm2) were tested to evaluate the effect of the chimney area on the combustion quality and combustion efficiency in terms of combustion products and gas consumption. Experimental results showed that reduction in the emission was realized by approximately 50% at both pressures of 17 mbar and 25 mbar when using higher chimney area. However, the gas consumption increased by approximately 0.67%, 1%, and 7% per m3 when the chimney with higher area was used at the burning temperature of 140 K, 180 K, and 220 K, respectively.

Simulation of the fluid dynamic and thermal behavior of an experimental passive cooling system of photovoltaic panels

Solar energy capacity has increased significantly globally, with values above 800 GW produced by different systems. Among these, PVT panels can generate either electricity, heat, or both. As these systems present various issues associated with excessive temperature increases, cooling systems have been developed to control the temperature using fluids such as water. The article uses previous data from the Technologic Institute of Sonora, which analyzed various cooling device configurations and selected the best two options (B1 and B4) based on the panel efficiency. Using the boundary conditions and the predicted streamlines, a simulation was made in CFD programs, determining the correct parameters to replicate the system fluid dynamics. Several simulations were carried out using different turbulence models. After comparing the temperature contour diagram and the streamline, it was obtained that the k-ω turbulence model best describes the fluid's behavior. The transient analysis simulations allow us to determine that the B1 configuration delivers the best cooling effect as it presents the most homogeneous temperature profile. BIAS and RMSE were calculated to validate and contrast the results obtained experimentally, obtaining values of 0.8675 and 1.8981, respectively.

Combined wind catchers and side windows for cross ventilation in row houses

Purpose This paper aims to explore the efficiency of natural ventilation in the bedrooms of typical two-storeyed row houses with newly reconfigured design that incorporate rooftop wind catchers and side windows to create cross ventilation. Design/methodology/approach A CFD program was used to assess average air velocity coefficient (Cv) in 32 airflow cases. Parameters include location of openings with respect to wind direction, inlet-to-outlet area ratio (IOR) and opening-to-floor area ratio (OFR). Findings The results reveal that indoor air velocities in the cases of air entering wind catchers are generally higher than those in the cases of air entering side windows while air velocities at the openings are the opposite. The IOR of 1:2 provides best results in terms of both velocities of the indoor air and velocities at the openings. Increasing the OFR from 20% to 50% generally improves indoor air velocities and airflow rates. Originality/value This study proved that the new solution of combining one-sided wind catchers and side windows can effectively solve the problem of ventilation uniquely existing in the conditions of typical row houses by catching prevailing wind from two opposite directions into multiple rooms. The results are given as non-dimensional air velocities, which can be interpreted with any climatic data, and therefore can be applied to row houses in any locations and climatic conditions. The findings can create a new and efficient design of row houses that benefits building industry.

Development and Verification of CFD Program by Central Difference Calculus for Incompressible Fluid

Development and Verification of CFD Program by Central Difference Calculus for Incompressible Fluid

Numerical and physical modeling of the aerodynamic process in a direct-flow coil-type boiler using a laboratory stand

The article examines the modes of gas passage through the chimney of a direct-acting steam generator set using a laboratory stand made of a cylindrical coil. The criterion for determining the gas flow regime is a dimensionless quantity called the Reynolds number. The air flow velocities and temperatures were determined experimentally. Based on these results, the Reynolds number was calculated and the flow regimes at each measurement point were determined, and the dependence of the Reynolds number on temperature and velocity was obtained, and the experiment was analyzed. With the help of the ANSYS program, a model of air movement on the stand was built. When deciphering the geometric model, the ANSYS SpaceClaim program was used. The model made it possible to estimate the distribution of the air flow velocity in the boiler model based on experimental values. Further, after constructing a geometric model using the ANSYS Icem CFD program, a dispersion model was cre-ated that showed the temperature distribution of flue gases in the external gas flow of the basic model of a direct-flow steam boiler. The processing of experimental data showed a further prospect of intensification of the heat exchange process in a direct-flow steam boiler of the coil type.

Analysis of the Aeroacoustic Characteristics of a Rigid Coaxial Rotor in Forward Flight Based on the CFD/VVPM Hybrid Method

This study develops a hybrid solver with reversed overset assembly technology (ROAT), a viscous vortex particle method (VVPM), and a CFD program based on the URNS method, in order to study the aerodynamic and acoustic characteristics of coaxial rigid rotors. The aerodynamic load of the “AH-1G” helicopter rotor is first calculated based on the hybrid method and compared with available experimental data. The prediction of the linear noise of the OLS rotor is then performed and the obtained results are compared with available experimental data. These results allow the evaluation of the accuracy of the hybrid method for emulating rotor aerodynamics and acoustics. Afterwards, the hybrid and CFD methods are applied to obtain the aerodynamic and acoustic characteristics of the given coaxial rigid rotor model, while taking into account the trim of the collective pitch. The obtained results demonstrate that the hybrid method has high proficiency in capturing blade–vortex-interaction impulsive loads and high computational efficiency in predicting associated loading noise characteristics. Furthermore, the effect of the hybrid method on the noise characteristics of coaxial rigid rotors under a different advance ratio, blade tip speed, shaft angle, and other conditions, as well as the impact of the upper and lower rotors on the noise contribution of the coaxial rotor are analyzed. Finally, the impacts of the initial phase and the vertical spacing on the sound pressure level are studied.

Optimization analysis of nuclear thermal coupling for a small nuclear thermal propulsion (SNTP) reactor

As a main structure, tie-tube elements are used both in the traditional and modern LEU nuclear thermal propulsion reactors. This complex structure and its corresponding complex convective heat transfer process have been studied, including CFD calculations. But these studies did not effectively evaluate the applicability of the models and typical problems. In this study, a general small nuclear thermal propulsion (SNTP) reactor model is established by using three-dimensional Monte Carlo code and commercial CFD program Fluent. The applicabilities of material properties, turbulence models and grids are clarified by analyzing various influencing factors. The calculation results show that due to the small enthalpy difference and heat transfer, the convection effect of inner flow based on hydrogen can be ignored. There is no factor that can significantly reduce the maximum fuel temperature, but the porosity of the insulator can significantly improve the heat transfer ratio. In terms of thermal safety and overall performance, 2:1 support ratio is still the best choice. Based on the simulation results, the phenomenon of steep temperature rise of outer tie-tubes is found, and the SST k-omega model with Y + <3 is recommended for simulation of similar problems.

Aerodynamic Improvements of Buses Inspired by Beluga Whales

The innovative bus designs, inspired by the whales, have been developed. The designs are confined to the frontal area of the buses. The new designs are named as the Beluga buses. Several variants of the models all mimicking Beluga whales are proposed. Both numerical analysis and experimental have been conducted to determine the drag coefficients of various models. The ANSYS CFD program was used for numerical simulations. WT tests were conducted to experimentally determine the drag coefficients. Both methods indicate that the beluga-inspired buses offer significant reductions in drag, which can lead to lower fuel consumption. The new beluga design is expected to reduce fuel consumption by 12.64%. Comparing the experimental and numerical results, a 6.4% discrepancy in the drag coefficients is observed at low Reynolds numbers, which became negligible at higher Reynolds numbers. The new geometry is expected to offer an economical solution for reducing fuel consumption.

Study on Condensed Matter Simulated by Multiphase Fluid-Solid Coupling Fluid Mechanics

The hydrodynamic characteristics of a three-phase gas-liquid-solid turbulent bed with light particle flow and intermittent liquid feeding were numerically simulated by CFD program Fluent6.3. The axial and radial motion of particles in a three-phase gas-liquid-solid turbulent bed and the variation of particle concentration in the bed are studied. The results show that the size and frequency of cavitation increase with the increase of the distance from the axis of the air distribution disk and the distance from the bed surface to the central region. The void varied from narrow to wide, while the void changed in the opposite direction. The bubble lift rate and bubble size are basically the same in axial and radial direction. With the increase of the surface gas velocity and the viscosity of the liquid phase, the average particle content in the bed decreases.

Residential Unit Design for Natural Ventilation in Tropical Multi-Family High-Rises With a Double-Loaded Corridor

This research investigates practical methods to improve the efficiency of natural ventilation in residential units of multi-family high-rises without additional areas. Typical studio- and one-bedroom-types of small units were redesigned using: 1) air post, 2) transom window, 3) buffer space with one corridor opening and 4) buffer space with two corridor openings. The simulation study using a CFD program to reveal that the indoor average air velocity coefficient (Cv ) in the best redesigned case (0.46) significantly improves from the base case (0.01). The paper demonstrates an example of application to an actual climate in Bangkok, Thailand. It was found that the proposed redesign using buffer spaces can considerably help upgrade the living conditions of the occupants in terms of both thermal comfort (24 hours vs. 0 hours in the comfort zone per day) and indoor air quality (24 hours vs. 8–17 hours that pass the minimum ventilation requirement per day) in the transitional month of February.

3D NUMERICAL STUDY OF HYDROYNAMICS AROUND A MONOPILE FOUNDATION UNDER COMBINED WAVE CURRENT EFFECT

A numerical investigation of hydrodynamics around a monopile foundation is presented in the paper. An open-source CFD program REEF3D is used for the present study. The REEF3D model solves the Reynolds-averaged Naiver-Stokes equation with k-w turbulence closure to obtain the flow hydrodynamics. The code utilizes a staggered cartesian grid system. Also, Message Passing Interface (MPI) based parallelization is used for domain decomposition. In order to ensure the precision of the flow field, the model is first validated for four different combined wave-current scenarios, where the currents and waves are following each other. The results obtained from the validation studies exhibit good agreement with the already reported experimental results. Initially, a grid convergence study has been performed to ensure that the Numerical wave tank is independent of the mesh size. Finally, numerical experiments corresponding to four different combined wave-current cases for different wave steepness are simulated using the code.

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

The evaluation of ship maneuverability characteristics typically involves the mode tests, direct CFD computations, and system-based simulations. The three methods have been widely used in traditional vessels. However, the trimarans, which are appended with the waterjet propulsion systems, have been rarely researched and assessed comprehensively based on the above methods. This paper used a free-running waterjet-propelled trimaran model test to obtain the constant turning and zigzag maneuvering performance in calm water conditions. By embedding the speed and heading controllers in a CFD program, along with the region moving method, a direct free-running maneuvering CFD model was established on a waterjet-propelled trimaran. Compared to the free-running model tests, the simulation results indicated that an empirical hydrodynamic derivative-based Maneuvering Model Group (MMG) method produced the fastest results but lacked accuracy in simulating a constant turning diameter, making it suitable for fast maneuvering estimation and prediction during the design stage. Conversely, a direct force (moment)-based CFD model required more accurate input estimates to acquire acceptable simulated results. Meanwhile, a body force-based CFD model considered more complex nonlinear impacts and was most similar to reality, achieving better agreement with the experimental results. Additionally, the simulations of the direct free-running maneuvering CFD model in calm and wavy water proved advantageous in examining hull-propulsor interaction during physically similar maneuvering processes where the model test was inadequate.