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![The coupled and segregated solvers comparison diagram, adapted with permission from [8].](profile/Alejandro-Alonzo-Garcia/publication/306447438/figure/fig1/AS:398690322796545@1472066588668/The-coupled-and-segregated-solvers-comparison-diagram-adapted-with-permission-from-8.png)
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This chapter is intended to present to readers a general scope of the technical, theoretical, and numerical applications of computational fluid dynamics using the finite volume method, restricted to incompressible turbulent flows (Ma < 0.3). The main objective of this chapter was to provide readers of a starting point to select an adequate numerica...
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... segregated mode solve them sequentially, taking the velocity and pressure equations (or corrected pressure equations) as the main variables, the coupled one solves globally the equations for continuity, momentum, and species exchange. Figure 1 shows a diagram of both solver modes' performances. ...
Citations
... The turbulence model selected for use in the simulation was the k-ω shear stress transport (SST) model. Through the literature review, this turbulence model was found to be best suited to predict the fluid behavior and heat transfer [69,[72][73][74][75][76][77]. ...
Stationary battery systems are becoming increasingly common worldwide with the number and capacity of installations simultaneously increasing. Large battery installations such as energy storage systems and uninterruptible power supplies can generate substantial heat in operation and while this is well understood, the thermal management systems that currently exist have not kept pace with stationary battery installation development. Stationary battery thermal management has long relied on active cooling as the default method of thermal management, yet there is an absence of academic research or comparative reviews for this method. The present work presents assessment of different active cooling methods through a computational fluid dynamics simulation validated with an experimental model. Following model validation, several cooling system configurations are analyzed in application to a full-scale stationary battery system. Specifically, the effects from the implementing either a perforated vent plate or vortex generators were observed. The vent plate was observed to greatly increase cooling performance while simultaneously promoting temperature uniformity between batteries. Vortex generators were shown to marginally increase cooling performance, yet future research is recommended to study the effects and improvement of the design. The results derived from analysis are intended to identify potential strategies that could be implemented or researched further for the improvement of active cooling systems.
... A staggered two-dimensional grid, Versteeg and Malalasekera [41]. . . . . 16 3.3 Flow chart for SIMPLE algorithm, Alonzo-Garcia et al. [44]. . . . . . . . 22 3.4 The grid arrangement at the boundary, Versteeg and Malalasekera [41]. . . 25 3.5 Periodic boundary condition, Joslin [19]. ...
... Flow chart for SIMPLE algorithm, Alonzo-Garcia et al.[44].(SOR), by considering the over-relaxation factor to be calculated as suggested for the optimum value in Hoffmann and Chiang[33]. ...
A direct numerical simulation (DNS) solver was implemented to study the hydrodynamic stability of the plane Poiseuille flow; the semi-implicit method for pressure-linked equations (SIMPLE) method was used as the core of the solver. The results of the DNS was compared to its corresponding results of the linear stability theory by solving Orr-Sommerfeld equation. The DNS solver was validated by solving some fundamental problems (e.g., lid-driven cavity, oscillating lid-driven cavity, and laminar channel flow problem) and comparing its results with the published results. Also, the Orr-Sommerfeld solver was implemented using the spectral collocation method. The solution of Orr-Sommerfeld equation is believed to be in good matching with the published results.
... For this purpose, the Simple algorithm is used. Also, for a better understanding of the simple algorithm, flowchart of this program is shown in Figure 2. [31] When executing the above algorithm, the isolated equations that are linearized must be solved. Because the problem is more than one dimension, it is not effective to use direct methods. ...
Heat transfer has always been one of the most important aspects of human life. So far, many sources have been reported on methods of increasing the heat transfer rate. Many of these methods focus on changes in equipment structure. These techniques can hardly cope with the growing demand for heat transfer and compression in equipment. Recent advances in nanoparticle production can be seen as a breakthrough in methods of increasing heat transfer. The purpose of this study is to numerically investigate the flow field and heat transfer of water-aluminium oxide nanofluid in a wavy channel. The channel consists of two parallel plates and is divided into three parts in the longitudinal direction. The beginning and end parts of the channel are insulated and the middle part is sinusoidal and receives a uniform heat flux. The nanofluid enters the channel at a uniform speed and temperature and exits it in an expanded manner. For numerical analyses, the finite difference method based on control volume and simple algorithm is used. In this research, Reynold’s effect was analysed. The results showed that by increasing the Reynolds number, the speed, temperature gradient and heat transfer rate was increased and the thickness of the thermal boundary layer was decreased. With increasing Reynolds number, the amount of heat transfer from the wall to the fluid and also the production of entropy increases. In the unsteady state, with increasing time and flow rate, the amount of heat transfer and total entropy and temperature gradient increase to reach the steady state.
... The mathematical model contains the equations that define the state of continuity and momentum and can thus be presented as follows [33,34]: ...
... The use of both equations proved to be effective for obtaining optimal results for turbulent fluid flow regimes. The basic equations are presented as follows [33,34]: ...
In this work, 3D models in classic configuration of Bach and Benesh rotor type, as well as models with modified blade pattern geometry were analyzed from the air circulation point of view inside the rotor enclosure in order to identify the operating parameters differences according to rotor geometric modified configuration. Constructive design aspects are presented, as well as results obtained from the virtual model analysis in terms of circulation velocity and pressure values which enhance rotor operation related to torque and power coefficients. The rotors design pattern is made according to previous results obtained by different researchers who have performed numerical analysis on virtual models and tests on the experimental rotor models using the wind tunnel. The constructive solutions are describing two-bladed rotor models, in four new designed constructive variants and analyzed using ANSYS CFX. The air velocity specific values, static and total pressure recorded at the rotor blade level are highlighted, that influence the obtaining of rotor shaft torque and power. Also torque coefficient (CT) and power coefficient (CP) values according with specific values of tip speed ratio (TSR) are presented for each analyzed case. The analysis results show higher power coefficient values for analyzed Bach V2 and Benesh V2 rotor modified models compared to the classic Bach and Benesh models for 0.3 TSR of 0.11–012 CP, 0.4 TSR of 0.18 CP (Benesh V2 model) and 0.27 CP at 0.6 TSR (Bach V2). The resulted values confirm that Benesh V2 model offers higher CP up to 5% at TSR 0.3, 2% at TSR 0.6 and 3% at TSR 0.4 compared to the Benesh classical model. The Bach V2 model offers 4% higher CP compared to the classic Bach model at TSR 0.6. Based on these results it is intended the further analytical and experimental research in order to obtain optimal rotor pattern.
A heat exchanger is a device that transmits heat energy from one object to another, or within the same object. Examples of heat exchanger include a boiler, an oven and a cooker. Experimental techniques for testing these devices make it more costly and time-consuming. Consequently, computational fluid dynamics (CFD) can manage heat exchanger systems and their performance with ease. The actual impacts of what is being examined may then be predicted computationally which yields a precise output with approximate results. The designed geometry includes a rectangular duct with an inlet, outlet and two obstacles of equal height. The Navier–Stokes equations for the fluid flow are used. During the meshing process, the continuous geometric space of an item is divided into thousands or more forms, which helps to correctly identify the object’s physical shape. The desired model is computed numerically. Finite volume method (FVM) is used to study the results at a low Reynolds number (around 2.3 × 106). The goal is to theoretically analyze the transmission of heat and fluid resistance to the flow. The CFD findings with experimental data are compared to confirm the model predictions. A CFD model based on the FVM and experimental data from a flow cell is used to study how fluid moves through ducts. This study focuses on the pressure, velocity and temperature fields of a fluid moving through a rectangular duct. As the top wall fluid temperature rises, the temperature distribution changes. Increasing fluid flow declines the temperature distribution. Temperature distribution grows with duct heat flow. As the flow rate rises, so does dispersion. Furthermore, as flow rate and velocity distribution drop, pressure distribution rises.
Horizontal Axis Tidal Turbines (HATT) currently have a lower power coefficient than commercially available wind turbines. This has meant that in recent years less funding goes towards developing such technology. Furthermore, some planned projects have not gone ahead, and there does not seem to be support from the government to promote its development. In the wind industry, turbines can have 5 times the rated power of a tidal turbine because the rotor size is not a problem. In the tidal industry, size is constrained due to technical and environmental factors. An approach to face this issue is to increase the power coefficient for a fixed rotor size. An experimental study is presented to investigate the performance of winglets fitted to a 1:20th scaled 1 m in diameter HATT. Winglets have been extensively employed in the aviation industry to reduce the vortices generated at the end of aircraft wings decreasing drag and hence increasing fuel economy of civilian aircraft. For horizontal axis turbines, winglets facing backwards on the suction side of the blades have been the subject of extensive research almost exclusively based on computer-driven numerical simulations as a means to increase the power capture of the rotor. With the use of oil-based paint flow visualisation, the mechanism behind the phenomenon affecting winglets facing the suction side has been identified as part of this work. Vortices form behind the blade/winglet interface when they are oriented towards the flow direction. These vortices reduce performance due to viscous effects. Power and thrust coefficients were measured from the scale HATT and together with numerical Blade Element Momentum simulations, the bending moments at the root could be calculated. A winglet facing downstream decreases the power coefficient by 12% in average and increases the thrust coefficient by an average 5%. On the other hand, a symmetrically mirrored winglet facing upstream can increase the power coefficient by around 1-2%, at the same time the thrust coefficient increases by 3-4%. Assuming that the increase in thrust is caused by fitting the winglets, their structural cost in the bending moment at the root of the blade is up to 40% more, 4.2-5.6% in this case. Cost-data from industry has suggested that even marginal increases in power coefficients due to winglets can provide a return on investment given the relative costs of blade manufacture and the expected level of subsides awarded to new and developing forms of electricity generation. Therefore, further work to optimise pressure-side winglets should be conducted.
This study focused on optimization of the power coefficient of floating offshore wind turbines (FOWTs) to maintain their wind power performance in order to overcome problems with the tilt angle resulting from an unstable wind turbine platform, which can reduce the effective area of wind turbine energy extraction. FOWTs with a variable-speed fixed-pitch control strategy were investigated using an experimental model in a wind tunnel and a CFD simulation model for analysis and comparison, using wind speeds of 2–5.5 m/s and tilt angles of 3.5–6.1°. The results showed that average rotational speed differences of 16.4% and optimal power coefficients of 0.35–0.36 could be maintained at tip speed ratios of 7.7–9.6 during wind speeds of 3–5 m/s with tilt angles of 3.9–5.8°. The results of this study provide insights into a new concept of power coefficient optimization using variable tilt angle for small to medium fixed pitch FOWTs, to reduce the cost of pitch control systems.
