CFD Letters

Application of Extended Eddy-viscosity and Elliptic-Relaxation Approaches to Turbulent Convective Flow in a Partially Divided Cavity

Gunarjo Suryanto Budi — 2024-05-31

The paper reports on the numerical turbulence model in predicting mass, momentum and heat transfer in a partially divided cavity heated from the side using buoyancy-extended eddy-viscosity and elliptic relaxation approach with the algebraic expressions for the Reynold stress tensor and turbulent heat flux vector. The CDS (central differencing scheme) and LUDS (linear upwind differencing scheme) were used as the discretization method and the governing equations were solved using the finite volume method and Navier-Stokes solver. Validation of the model has been carried out by experimental data of convective flow in the cavity as well as by numerical data DNS (direct numerical simulation). The model agrees very well with the experiment and DNS and it is also able to demonstrate the performance which is comparable to that of the previous advanced second-moment closure model (SMC) in the literature. The results show that the model is suitable for use in simulations of the turbulent convective flow in a cavity with partition and it has the potential to be applied to more complex cavities and a wide range of turbulence levels.

Numerical Analysis into the Improvement Performance of Ducted Propeller by using Fins: Case Studies on Types B4-70 and Ka4-70

Berlian Arswendo Adietya — 2024-05-31

Numerical analysis was conducted to assess the impact of fins on the B4-70 and Ka4-70 propeller performance. The study explored different fin variations, specifically bare fins, Propeller Boss Cap Fins (PBCF), and propeller nozzles, using computational fluid dynamics (CFD) simulations. To obtain the best results, the researchers utilized the explicit algebraic stress model (EASM) based on Reynolds-Averaged Navier-Stokes (RANS) equations and turbulence modelling. The primary goal of this study was to improve the energy efficiency of ships by examining various propeller configurations, both open and ducted. The overall conclusions indicated that the B4-70 PBCF convergent and Ka4-70 PBCF divergent with the addition of nozzle 19A exhibited the highest efficiency based on the EASM analysis. The CFD simulation results for both B4-70 and Ka4-70 propellers, utilizing a nozzle 19A with added boss cap fins, revealed several noteworthy phenomena. Firstly, for the B4-70 propeller, efficiency (η0) at J = 0.6 to J = 0.8 showed an increase of 1% to 2%. Secondly, concerning the Ka4-70 propeller, efficiency (η0) at J = 0.6 to J = 0.8 increased by 2% to 10%. These findings clearly demonstrate that the use of an ESD, such as the nozzle 19A with added boss cap fins, enhances the propulsion performance of the ship. It is evident that the CFD approach remains suitable and reliable for overall simulations.

Savonius-Magnus Hybrid Turbine Design Performance Based on Computational Fluid Dynamics

Rr. Heni Hendaryati — 2024-05-31

Savonius turbine is a vertical-axis wind turbine (VAWT), which has the advantage of being able to capture wind from different directions. This turbine is suitable for high turbulent wind areas. The blade on the Savonius turbine used in this study is equipped with a Magnus rotor with dimensions of 120 mm in diameter and 720 mm in height. The main purpose of this study is to determine the torque and pressure generated by turbines with three and four blades. The design was then tested numerically with variations in wind velocity. The simulation model was created using computer-aided design software, namely Autodesk Inventor 2023, and then inputted into computational fluid dynamics (CFD) software, namely Ansys Workbench 2022 R2. Wind velocities were varied by 3, 5, 7, 9, and 11 m/s and simulated using transient time with constant wind velocity. The result of this study is that the largest pressure is generated by a hybrid turbine with four blades at a wind velocity of 11 m/s. The results show that the torque and wind pressure that occurs in three- and four-blade hybrid turbines tend to rise; the faster the wind, the higher the torque and pressure of both hybrid turbines

Performance Investigation of PEM Fuel Cell with Three-Pass Serpentine Flow Fields under Varying Operating Voltages

Kaoutar Kabouchi — 2024-05-31

The fuel cells performance is significantly impacted by both design and operational factors. The effective distribution of reactants within the flow fields is facilitated by the design of the flow channels. Therefore, the geometry of the flow channels and the overall design of the flow field play a crucial role in determining the fuel cells performance. Among various flow field designs, the serpentine flow field demonstrates superior performance compared to others. In this research, a three-dimensional proton exchange membrane fuel cell model was developed and used to study the influence of three-pass serpentine flow field on cell performance across varying operating voltages (0.9 V, 0.7 V and 0.5 V). The purpose of this research is to simulate and evaluate the comportment of the three-pass serpentine flow channels configuration by analyzing several parameters such as channels velocity distribution, oxygen mole fraction, pressure distribution and electrolyte current density along the z-axis at the cathode under different operating voltages. Numerical simulations were conducted using the COMSOL Multiphysics software. Therefore, this software is used to solve numerically the complete three-dimensional model with the governing equations of charge conservation, species transport, momentum, and continuity. The obtained results indicate that among different operating voltages, the cell voltage of 0.5 V demonstrated the highest channels velocity distribution, pressure distribution, and electrolyte current density. Moreover, it is found that at an operating voltage of 0.5 V, there is an important decrease in oxygen concentrations indicating a significant oxygen consumption in the fuel cell which improves the overall efficiency. This work contributes valuable insights to the optimization of fuel cell performance, specifically highlighting the favorable outcomes associated with the three-pass serpentine flow field design at lower operating voltages

Transient Analysis on the Crosswind Effect to the Aerodynamics of High-speed Train Travelled on the Bridge Between Two Tunnels at Jakarta -Bandung Track

Harinaldi Harinaldi — 2024-05-31

The rapid evolution of global transportation technology is exemplified by Indonesia's innovative high-speed train initiative, linking Jakarta and Bandung in an impressive 45 minutes. Operating at 350 km/h, the HST CR400AF underscores the importance of aerodynamics in high-speed rail systems. This study delves into the significant impact of crosswind on key aerodynamic factors (drag, lift, rolling moment) within the tunnel-bridge-tunnel configuration. Leveraging Computational Fluid Dynamics (CFD) through ANSYS FLUENT, the analysis explores crosswind variations at 0 m/s, 10 m/s, and 25 m/s. Results reveal a proportional increase in aerodynamic load with higher crosswind intensities: 1.67 times for drag, 58.8 times for lift, and 29.8 times for rolling moment. Notable observations include pronounced aerodynamic load fluctuations during the "OUT" process, with the head section bearing the greatest load, followed by the tail and middle sections. These findings contribute valuable insights to the global discourse on enhancing safety and efficiency in high-speed rail systems

Improving the Performance of a Forced-flow Desalination Unit using a Vortex Generator

Dan Mugisidi — 2024-05-31

Water is a primary need for living creatures, and water scarcity can trigger a crisis. Water scarcity is becoming an issue in Indonesia, especially in coastal village areas, including salt-producing areas. Salt production involves evaporating large amounts of seawater in concentration ponds. Using evaporated seawater as a source of clean water would reduce the risk of water scarcity. Therefore, this study aims to obtain fresh water by condensing water vapour that evaporates in a desalination unit. More specifically, the study uses a vortex generator to increase the rate and efficiency of evaporation in a forced-flow desalination unit. This research was conducted indoors to reduce uncontrollable variables. An evaporation container with a volume of 0.35 m3 was filled with seawater. The rate of evaporation in the desalination unit with a vortex generator was compared to that in a unit without a vortex generator. The results show that the vortex generator leads to faster evaporation. The rate of evaporation with a vortex generator was 13% higher than that without a vortex generator, and the gained output ratio increased 14% with the vortex generator. Therefore, it can be concluded that vortex generators can improve the performance of desalination equipment

Numerical Investigate the Effect of Turbulence Models on the CFD Computation of Submarine Resistance

Hien Le Tat — 2024-05-31

Up to now, there is no developed ‘universal’ turbulence model in CFD simulation, so employing an appropriate turbulence model is crucial for accurately predicting the hydrodynamics of a ship, especially for submarines. This study focuses on investigating the impact of turbulence models on the predicted results in frictional and pressure resistance components and flow features around the submarine at different ship velocities by the CFD method. Four various turbulence models consisting of the Reynolds Stress Model, realizable k-ε two-layer, standard k-ω, and SST k-ω turbulence models are investigated in this study. The obtained numerical results demonstrate variations in resistance and the flow patterns around the submarine due to the effect of turbulence model. Based on the obtained results, the paper points out that, the choice of turbulence model significantly affects the frictional resistance of the submarine and the SST K-ω turbulence model provided the highest level of accuracy in comparison with experimental data. The model employed in this research is the DARPA SUBOFF submarine model

A Novel Poly (vinylidene) Fluoride/TiO2/Spent Bleaching Earth for Enhancing Hydrophilic Hollow Fibre Membrane

Rhafiq Abdul Ghani — 2024-05-31

Nowadays, polymer as the raw material has been utilized in the development of Hollow Fibre (HF) membranes. PVDF is a commonly used for HF membrane material. However, it has hydrophobicity properties and lead membrane becomes low permeability and fouling. Therefore, to avoid these membranes problems, the incorporation of inorganic nanoparticles into PVDF membranes matrix is necessary to be applied for significantly improving PVDF membranes performance. This study investigates the characteristics and performance of PVDF-TiO₂ HF membranes using spent bleaching earth (SBE) as a promising material from industrial waste as a renewable inorganic nanoparticle. This novel PVDF-TiO₂-SBE HF membrane was fabricated using the subsequent steps: The preparation process incorporates SBE revival through solvent extraction and thermal treatment alongside the wet spinning technique for membrane fabrication. The Fourier transform infrared (FTIR) functional groups, scanning electron microscope (SEM) morphology, water contact angle and pure water flux performance were investigated to specifically understand the performance of this typical HF membranes. The IR results show that Si-O-Si groups were found in the membrane matrices due to the addition of SBE material. The addition of TiO₂-SBE particles also indicate a sandwich (sponge-finger-like) morphological structure on the cross-sectional, a rough and porous surface structures. The hydrophilic properties of the HF membrane and pure water flux performance are determined by the composition of the TiO₂-SBE mixture added as an additive material. The minimum contact angle found at 74.33°, while the water flux is 5.81 kg.m^-2.h^-1 on the identical HF membrane. Accordingly, this approach significantly enhances the properties of the pure PVDF HF membrane.

Numerical Model Parameters Choice of Helical Savonius Wind Rotor: CFD Investigation and Experimental Validation

Mariem Lajnef — 2024-05-31

Electrical power is essential for human beings welfare. The available wind as a clean and renewable source of energy has whetted extensive interest over decades. Savonius vertical axis wind rotor as an energy converter has the merit of being adequate for specific implementations owing to its lower cost and independency on wind direction. From this perspective, multiple studies have been conducted to boost its efficiency. This research work emphasizes on the helical Savonius wind rotor (HSWR). The basic objective is to investigate the impact of selecting the numerical model parameters on its aerodynamic and performance characteristics. Experimental tests were realized with a 3D printed HSWR in a wind tunnel. The experimental performances in terms of power, static and dynamic torque coefficients were addressed. Next, a numerical study was undertaken through Ansys Fluent 17.0 software. Grid, turbulence model and rotating domain size tests were examined. Good accordance was obtained, which validated the numerical model with an averaged error of 5%. The maximum power coefficient proved to be equal to 0.124 at a tip speed ratio of 0.73 and 0.1224 at a tip speed ratio of 0.69, respectively, numerically and experimentally

Evaluation of Heat Transfer and Fluid Dynamics across a Backward Facing Step for Mobile Cooling Applications Utilizing CNT Nanofluid in Laminar Conditions

Afrah Turki Awad — 2024-05-31

In a variety of engineering applications, the efficacy of heat dissipation in mobile cooling systems is greatly influenced by the Backward Facing Step. Its significance in optimizing cooling solutions for mobile devices is highlighted by the fact that its design and fluid dynamics are crucial in minimizing skin friction and improving passive heat transfer. In this paper, we present a verification of an advanced numerical model for heat transfer and fluid flow through a Backward Facing Step, used in mobile cooling. The objective of this study is to explore fluid separation, a method enhancing passive heat transfer and reducing skin friction. ANSYS/FLUENT software has been used to solve the backward facing step in a horizontal duct filled with pure water. Carbon nanotube (CNT) dispresed into the base fluid at different volume fractions of 0.2%, 0.65%, and 1%. This study focused on laminar flow conditions ranging from Reynolds numbers 200 to 900. In order to reduce the computation time and ensuring the accuracy and reliability of numerical simulations, a grid independence study has been conducted. The findings revealed a substantial rise in the average Nusselt number and heat transfer coefficient with increased Reynolds number and volume fraction of nanoparticles. Specifically, the nanofluid (CNT/water) exhibited the highest average Nusselt number and heat transfer coefficient with volume fractions 1%. Furthermore, the research showed a decrease in the skin friction factor as both Reynolds number increased and nanoparticles’ volume fraction decreased. The increments of nanoparticles' concentrations lead to increase viscosity, promotes agglomeration, alters flow behaviour by inducing turbulence, and enhances heat transfer. These factors collectively contribute to higher skin friction due to increased resistance to fluid flow and disrupted streamline patterns