CFD Letters

Analysis of Mesh Resolution Effect to Numerical Result of CFD-ROM: Turbulent Flow in Stationary Parallel Plate

Candra Damis Widiawaty — 2024-03-31

Computational fluid dynamics (CFD) is extensively utilized to predict flow behaviour in various industries and applications. The Full Order Model (FOM) is a high-accuracy approach to flow modelling, but it requires significant computational resources due to its high order and thousands of variables. To address this problem, the Reduced Order Model (ROM) was developed. Despite the advancement brought by ROM, there is a notable gap in research concerning the impact of mesh configuration on CFD-ROM results. While the number of modes has been extensively studied for its influence on CFD-ROM, the mesh configuration, a critical aspect of the simulation process, has received relatively limited attention. This study investigates the effect of mesh resolution on numerical results in CFD-ROM concerning turbulent flow within stationary parallel plates. Employing rigorous methods, including Richardson Extrapolation, verification, validation, and error percentage. The results explicitly confirm that mesh resolution directly impacts the numerical results of the velocity field in CFD-ROM. It is found that there is a notable reduction in Convergence Grid Index (CGI) values for different mesh ratios: 6.401% for medium-to-coarse and 2.031% for fine-to-medium ratio. Thus, with the same mode number, mesh resolution selection can enhance the numerical result of the velocity field in CFD-ROM.

Impact Tip Speed Ratio in Performance Analysis for Horizontal Axis Wind Turbine (HAWT) with Optimal Twist and Tapered (OPT) Blade Shape

MUHAMMAD AL.AIN MAT ZIN — 2024-03-31

Performance for Horizontal Axial Wind Turbine (HAWT) is influenced by the difference in tip speed ratio (TSR) and mesh distribution. The objective of this article is to study the optimal performance of wind turbines when subjected to different mesh resolution, TSR and wind speed velocity.Therefore, it is important to study the effects of different mesh resolutions in terms of wind turbine performance. To achieve that, a 0.65m optimal twist and tapered (OPT) blade is used with various inlet velocities and TSR. This study uses the k-ꞷ shear-stress transport (SST) based Reynold-Average Navier Stokes (RANS) approach in commercial ANSYS Fluent CFD software. This simulation was performed using the Moving Ratio Frame (MRF) method. To find the optimum grid resolution, a Grid Independence Test (GIT) was conducted comparing the coefficient of power (Cp). From the RESULT, TSR 6 shows the best HAWT performance when Cp for inlet velocity 8 m/s is 0.2608.

Analysis and Prediction of Equivalent Diameter of Air Bubbles Rising in Water

Gabriel de Carvalho Nascimento — 2024-03-31

The equivalent diameter of rising bubbles in liquids is an important parameter that has been investigated for decades by researchers for different purposes. Bubble diameter plays important role in quantifying oil and gas leaks in subsea leak analysis, since it allows the prediction of the magnitude of leaks in seabed petroleum wells and other structures through images obtained by underwater vehicles at great depths. Most studies available in the literature on the subject focus on investigating air bubbles in water; therefore, they were used as the main guide of the experimental apparatus described in this article. Several tests were conducted with air bubble chain in tap water, whose flow rate ranged from 21.1 mL/min to 234.4 mL/min, whereas the bubble equivalent diameter ranged from 4.1 mm to 8.2 mm. In addition, computational fluid dynamics simulations were carried out for comparison purposes; they were validated as potential tools to help designing an automated subsea gas leakage monitoring system based on image analysis algorithms. The herein proposed model could be both analytically and experimentally validated, based on comparisons to findings reported by other authors. This procedure enabled gathering evidence about the most efficient analytical predictions available in the literature for the herein addressed scenario. The results in the present study are consistent to those recorded in the main related articles.

A Comparative Study on Hydrodynamic Analysis with and without Cavitation Modelling: A Study on Textured Slip Journal Bearing

Althesa Androva — 2024-03-31

In journal bearing modeling, the phenomenon of cavitation is very important to improve the accuracy of the simulation results. This is because cavitation will almost certainly occur because there are convergent and divergent geometries. The results of the simulation will be close to real conditions so that it can have a positive effect on researchers in order to design optimal journal bearings. The effect of modeling without cavitation and with cavitation on journal bearing modeling has a great influence on the lubrication performance of journal bearings. In modeling with cavitation, the maximum hydrodynamic pressure and load carrying capacity that the journal bearing is capable of relying on has a fairly rapid increase. The modeling results also relate to the friction force that occurs in the journal bearing. The aim of the present study is to explore the effect of inclusion of modeling of the Hydrodynamic pressure. The finite volume method based on software is used to compare the result with and without cavitation. Here, The mixture multiphase cavitation is adopted. The numerical result show t he effect of modelling without cavitation and with cavitation on journal bearing modelling has a great influence on the lubrication performance of journal bearings. In modelling with cavitation, the maximum hydrodynamic pressure and load cmarrying capacity that the journal bearing is capable of relying on has a fairly rapid increase. The modelling results also relate to the friction force that occurs in the journal bearing.

Numerical Prediction of Trailing Edge Noise at Low Reynolds Number with Modified Trailing Edges of a NACA 0015 Airfoil

Mohamed Ibren — 2024-03-31

Global concern about high noise levels in areas near airports and wind farms has generated interest from various groups due to factors such as potential health problems and dissatisfaction among the local community. To accommodate this worthwhile plan of further reducing overall noise levels, some researchers are working on lowering the contribution of trailing-edge noise. The original scientific contribution of this study lies on understanding the efficiency of various trailing edge designs such as baseline, serrations, comb and comb-serrated, across different angles of attack and Reynolds numbers, while also addressing the limitations of existing geometrical models for trailing edges. The study intends to examine the performance of these different configurations, with an emphasis on their effect on acoustic responses. By utilizing large-eddy simulation and applying the Ffowcs-Williams and Hawkings models for noise prediction, an investigation was conducted to assess the impact of these trailing edge configurations on radiated noise at a low Reynolds number of 1.6× 105. The numerical predictions of lift coefficient and surface pressure fluctuations are compared and validated with a published study and experimental data, showing satisfactory results. Further analysis of these study has demonstrated that prominent peaks at lower frequencies (<103) are observed, which are identified as the characteristic frequencies. Moreover, results showed irregular broadband noise (300 - 600 Hz) with increased noise and shifting peak frequency as angle of attack rose. The serrated trailing edge design notably reduced noise levels by roughly 21 dB, especially for low frequencies. Comb-serration increased high-frequency noise by about 9 dB for angles of attack at 0, -1, and -20, and achieved a reduction of approximately 9 dB for angles of attack at 1 and 20. On the other hand, the directivity pattern showed that the maximum noise level is observed to predominantly radiate at an azimuth angle of around 90 degrees for all the cases, ranging from 900 to 2700, indicating that the majority of the source's acoustic energy is being emitted on the suction and pressure sides of the airfoil.

Numerical Study of the Air Outlet Effect Inside a Living Room Connected to an Aerovoltaic Solar Air Heater

Slah Driss — 2024-03-31

In Sfax–Tunisia, Fossil fuels such as coal, fuel oil and natural gas, are the principle elements responsible for heating of buildings. The problem of pollution result is from the blazing of these fossil fuels and the dramatic increasing in the price of electricity. Thus aerovoltaic solar air heater (ASAH) appears to be a suitable and inexpensive technique for supplying hot air to heat buildings in the sunny area. The idea behind this paper is to employ the ASAH to improve the indoor air quality and thermal comfort by connecting the room and the panel through the use of a pipe. The objective of this work is to develop the design of ASAH and to study numerically the aerodynamic and thermal structures during the heating of a living room connected to an ASAH by means of ANSYS Fluent 17.0.Numerical simulation, implementing a RNG k-ɛ turbulence model, shows that this technique has a positive effect to improve the thermal comfort in a living room. Thus, it is suggested to employ an ASAH to heat buildings.

Simulation Approach of Photovoltaic Thermal Based on Water Collector with Rectangular Model

Muhammad Zohri — 2024-03-31

The advancement of PVT technology in the contemporary era is experiencing an upward trend. This phenomenon can be attributed to the growing societal demand for energy, particularly renewable energy derived from solar sources. The present study investigates the rectangular configuration of a water-based heat absorber within a photovoltaic-thermal (PVT) system. The rectangular model PVT system was simulated using nine different mass flow rate of water variations within the rectangular model channel. The dataset has nine mass flow rate of water variants ranging from 0.001 kg/s to 0.009 kg/s, as well as six solar radiation variations: 500 W/m2, 600 W/m2, 700 W/m2, 800 W/m2, 900 W/m2, and 1000 W/m2. The maximum average outlet temperature achieved under 1000 W/m2 solar radiation is 50.53%, given a 0.001 kg/s fluid mass flow rate. The maximum average photovoltaic (PV) efficiency is 11.93% when exposed to 500 W/m2 solar radiation intensity. The maximum average photovoltaic-thermal (PVT) efficiency is 76.23% when exposed to 500 W/m2 solar radiation intensity. Therefore, utilizing rectangular collectors in water-based photovoltaic-thermal systems potentially substantially enhanced the average thermal efficiency and overall PVT efficiency. Consequently, it is advisable to consider incorporating rectangular collectors in the future improvements of PVT technology.

Enhancing Electric Vehicle Battery Thermal Management using Phase Change Materials: A CFD Analysis for Improved Heat Dissipation

Divyashetty — 2024-03-31

The adverse environmental issues and climate change has compelled world to shift to renewable energy systems. Conventional IC engines are the major contributor for air pollution which is the main cause for the global warming. Therefore, EVs (Electric Vehicle) are the future of the automotive industry. The important issues faced by EVS are battery heat generation. Hence in order to remove heat efficiently from the EV battery CFD analysis of a passive thermal management system using PCM for Li-ion batteries is studied for three different discharge rates. Compared to bare cell, the cell with passive BTMS reduces the maximum temperature rise by 2%, 2.1% and 1% at discharge rates of 1.5 C, 1.0 C and 0.5 C respectively thus implying that the BTMS adopted is effective in removing heat from the surface of the cell.

The impact of mechanical ventilation on Sfax City's greenhouse microclimate

Hamza Chiboub — 2024-03-31

The greenhouse serves as an enclosed structure designed to create a conducive environment for agricultural productivity, irrespective of the challenges posed by seasonal variations. Recognizing the contemporary complexities in agricultural management, our research endeavors involve the development of a comprehensive numerical model and the establishment of an experimental setup to delve into the nuanced impact of mechanical ventilation. Specifically, the study investigates the influence of four different entrance velocity values on airflow dynamics within agricultural greenhouses. The results illuminate the direct correlation between inlet velocity and various crucial variables, including temperature distribution, velocity field distribution, DO irradiation distribution, and static pressure distribution. Notably, at Vint = 12 m.s-1, the maximum temperature remains below Tmax = 307 K, while at Vint = 3 m.s-1, it reaches Tmax = 327 K. This underscores the pivotal role of accurate modeling and control for the optimal management of agriculture in the central region of Tunisia, particularly in Sfax.

Numerical Analysis of the Co-firing Combustion of Coal and Palm Shell Kernel In Stoker Boiler

M. S. K. Tony Suryo Utomo — 2024-03-31

The United Nations Framework Convention on Climate Change (UNFCCC) states that Indonesia is committed to contributing to global climate change solutions. The government will also continue to encourage the development of a number of renewable energy (EBT)-based power generation projects. This is based on the use of renewable energy which is still low, namely around (1.9%) 8215.5 MW. Meanwhile, the potential for EBT to become energy can be around 443,208 MW. One source of EBT in Indonesia that can be utilized is Biomass. Co-firing of biomass is a relatively cheaper option and does not require investment in new power plants. However, Co-firing combustion has several aspects that need to be studied, such as temperature combustion and the generation of gas emissions. Therefore, this study aims to determine the temperature and the emissions resulting from co-firing of palm kernel shell biomass. This research was conducted using the Computational Fluid Dynamics method on stoker boiler model. The test parameters of the research was the maximum and average temperatures in the furnace, and the average and maximum fractions of CO2, SO2 in the stoker boiler furnace. From the research conducted, it was found that the resulting combustion temperature decreased as the co-firing fraction of the biomass increased. However, CO2 gas emissions increased and SO2 decreased with increasing fraction of co-firing biomass which showed a decrease in harmful gas emissions and complete combustion that occurred in the furnace.