Fluid dynamic characterization of vortex generators and two-dimensional turbulent wakes

The main objective of this PhD thesis is the fluid dynamic characterization of the flow behind vortex generators (VG) as well as to investigate their influence in the separation of the boundary layer. CFD simulations have been carried out for the analysis of the flow downstream a single vortex generator on a flat plate. In order to evaluate the induced flow effect of the VG, a test case of a single rectangular VG has been designed and the flow have been numerically simulated and analyzed. Three-Dimensional steady state simulations at low Reynolds number have been performed using EllipSys3D CFD code and the computational results have been compared with experimental data. The self-similar behavior and the helical symmetry on the VG induced flow have been studied. The computations have demonstrated considerable reliability when reproducing the physics of the VG by a rectangular vortex generator. Furthermore, a detailed analysis of the equilibrium parameters has been made on a two-dimensional turbulent wake in two different test cases: a twin-plate and a symmetric airfoil (NACA0012). Both cases have been numerically analyzed and the computational results have been compared with experimental observations. The self-similar behaviour on the wake generated by a twin-plate and a symmetric airfoil has been tested and the CFD results match the experimental observations reasonably well.This thesis has been divided into five main parts:PART I. In this part is presented the importance of this research as well as the main motivation to carry out such work. An extensive description of the state of the art on vortex generators models is presented with high emphasis on wind turbine applications. Further, a very detailed explanation of the state of the art on self-similarity and on two-dimensional turbulent wake equilibrium is given.PART II. The three chapters of this part comprise the foundation of this thesis. In this part there is a detailed description of the vortex generator models used in this research, as well as a comparison of the computational results with the wind tunnel experiments carried out by Clara M. Velte, as a validation tool of the computations. The implementation of the BAY model into the EllipSys CFD code is described in Chapter 5 and it was performed in conjunction with N.N. S?rensen and P.E. Rethore. Finally a parametric study of the device angle dependency of a single VG on a flat plate is described in Chapter 7. Four different angles of attack have been selected for this parametric study: 20º, 25º, 30º and 35º.PART III. In this part, a self-similarity analysis has been made on a single rectangular VG on a flat plate. The simulations were able to capture the helical behaviour of the vortex generator wake with good accuracy when comparing with the experimental data. A very detailed description of the downstream evolution of the helical parameters in the computations is presented in this chapter 8 and compared with experimental results

Computational Modeling of Gurney Flaps and Microtabs by POD Method

Gurney flaps (GFs) and microtabs (MTs) are two of the most frequently used passive flow control devices on wind turbines. They are small tabs situated close to the airfoil trailing edge and normal to the surface. A study to find the most favorable dimension and position to improve the aerodynamic performance of an airfoil is presented herein. Firstly, a parametric study of a GF on a S810 airfoil and an MT on a DU91(2)250 airfoil was carried out. To that end, 2D computational fluid dynamic simulations were performed at Re = 10(6) based on the airfoil chord length and using RANS equations. The GF and MT design parameters resulting from the computational fluid dynamics (CFD) simulations allowed the sizing of these passive flow control devices based on the airfoil's aerodynamic performance. In both types of flow control devices, the results showed an increase in the lift-to-drag ratio for all angles of attack studied in the current work. Secondly, from the data obtained by means of CFD simulations, a regular function using the proper orthogonal decomposition (POD) was used to build a reduced order method. In both flow control cases (GFs and MTs), the recursive POD method was able to accurately and very quickly reproduce the computational results with very low computational cost.The current research was partially supported by the Spanish Government with the Project: grant number: MTM2015-64577-C2-1-R

Comparisons of SVM Kernels for Insurance Data Clustering

This paper will study insurance data clustering using Support Vector Machine (SVM) approaches. It investigates the optimum condition employing the three most popular kernels of SVM, i.e., linear, polynomial, and radial basis kernel. To explore sum insured datasets, kernel comparisons for Root Mean Square Error (RMSE) and density analysis have been provided. It employs these kernels to classify based on sum insured datasets. The objective of this research is to demonstrate to industrial researchers that data grouping may be accomplished in an organized, error-free, and efficient manner utilizing R programming and the SVM approach. In this study, we check the insurance data for the sum insured with statistical methods in the form of Model Performance Evaluation (MPE), Receiver Operating Characteristics (ROC), Area Under Curve (AUC), partial AUC (pAUC), smoothing, confidence intervals, and thresholds. Then, sum insured data are followed up to classify using SVM kernels. This paper finds new ideas for evaluating insurance data using the SVM approach with multiple kernels. This novel research emphasizes the statistical analysis methods for insurance data and uses the SVM method for more accurate data classification. Finally, it informs that this research is a pure finding, and there has never been any research on this subject. This research was conducted using the sum insured data as a sample from the Office of the Insurance Commission (OIC) in Thailand as an independent insurance institution providing actual data. Doi: 10.28991/ESJ-2022-06-04-014 Full Text: PD

Computational analysis of radiative heat transfer due to rotating tube in parabolic trough solar collectors with Darcy Forchheimer porous medium

This attempt numerically investigates the heat transfer in parabolic trough solar collectors due to the rotating tube for the hybrid nanofluid flow over the Riga surface with Darcy Forchheimer’s porous medium under the effect of solar radiation. The influences of viscous dissipation and Joule heating are also considered. Equations governing the fluid flow are non-dimensionalized by implementing appropriate similarity variables. The resulting non-dimensionalized ordinary differential equations are solved using the shooting technique with Adam Bashforth and Adam Moulten’s fourth-order numerical approach. The numerical outcomes for various influential physical parameters regarding the fluid velocity, temperature, Nusselt number, and entropy generation are presented in graphical form. It is observed that the thermal profile escalates with the higher values of Reynold’s number, modified magnetic field parameter, and Prandtl number. Also, the Nusselt number diminishes with augmenting values of the Eckert number, modified magnetic field parameter, Forchheimer number, and Darcy number. The optimization of heat transfer in parabolic trough collectors is essential to improve the performance of solar collectors. The concentrated solar power technology is adequate for storing radiation energy in higher amounts.Author U.F.-G. appreciates the support of the Government of the Basque Country, Grant N. ELKARTEK 22/85 and ELKARTEK 21/10. The research is supported by Researchers Supporting Project number (RSP2023R158), King Saud University, Riyadh, Saudi Arabia

Power Control Optimization of an Underwater Piezoelectric Energy Harvester

Over the past few years, it has been established that vibration energy harvesters with intentionally designed components can be used for frequency bandwidth enhancement under excitation for sufficiently high vibration amplitudes. Pipelines are often necessary means of transporting important resources such as water, gas, and oil. A self-powered wireless sensor network could be a sustainable alternative for in-pipe monitoring applications. A new control algorithm has been developed and implemented into an underwater energy harvester. Firstly, a computational study of a piezoelectric energy harvester for underwater applications has been studied for using the kinetic energy of water flow at four different Reynolds numbers Re = 3000, 6000, 9000, and 12,000. The device consists of a piezoelectric beam assembled to an oscillating cylinder inside the water of pipes from 2 to 5 inches in diameter. Therefore, unsteady simulations have been performed to study the dynamic forces under different water speeds. Secondly, a new control law strategy based on the computational results has been developed to extract as much energy as possible from the energy harvester. The results show that the harvester can efficiently extract the power from the kinetic energy of the fluid. The maximum power output is 996.25 mu W and corresponds to the case with Re = 12,000.The funding from the Government of the Basque Country and the University of the Basque Country UPV/EHU through the SAIOTEK (S-PE11UN112) and EHU12/26 research programs, respectively, is gratefully acknowledged. The authors are very grateful to SGIker of UPV/EHU and European funding (ERDF and ESF) for providing technical and human

Computational Modelling of Three Different Sub-Boundary Layer Vortex Generators on a Flat Plate

Flow separation is the source of several problems in a wind turbine including load fluctuations, lift losses, and vibrations. Vortex generators (VGs) are passive flow control devices used to delay flow separation, but their implementation may produce overload drag at the blade section where they are placed. In the current work, a computational model of different geometries of vortex generators placed on a flat plate has been carried out throughout fully meshed computational simulations using Reynolds Averaged Navier-Stokes (RANS) equations performed at a Reynolds number of Re = 2600 based on local boundary layer (BL) momentum thickness = 2.4 mm. A flow characterization of the wake behind the vortex generator has been done with the aim of evaluating the performance of three vortex generator geometries, namely Rectangular VG, Triangular VG, and Symmetrical VG NACA0012. The location of the primary vortex has been evaluated by the vertical and lateral trajectories and it has been found that for all analyzed VG geometries the primary vortex is developed below the boundary layer thickness = 20 mm for a similar vorticity level (wxmax). Two innovative parameters have been developed in the present work for evaluating the vortex size and the vortex strength: Half-Life Surface S05 and Mean Positive Circulation 05+. As a result, an assessment of the VG performance has been carried out by all analyzed parameters and the symmetrical vortex generator NACA0012 has provided good efficiency in energy transfer compared with the Rectangular VG.This research was partially funded by Fundation VITAL Fundazioa

Thermosolutal natural convection energy transfer in magnetically influenced casson fluid flow in hexagonal enclosure with fillets

Current disquisition is aimed to adumbrate thermosolutal convective diffusion transport in Casson fluid filled in hexagonal enclosure under effectiveness of inclined magnetic field. Partially iso-concentration and iso-temperature distributions at base wall of enclosure is provided along with incorporation of fillets at corners of flow domain. Governing formulation in 2D are expressed in a velocity-pressure, energy and concentration bal-ance equations. Numerical computations are executed by employing COMSOL Multiphysics software based on finite element scheme. Domain discretization in manifested by performing hybrid meshing in view of 2D ele-ments. Linear and quadric interpolating polynomials for pressure and other associated distributions are capi-talized. Non-linearized discretization system is handled by non-linear solver renowned as PARADISO. Results and code validation is assured by performing comparison and grid convergence test respectively. The impact of flow concerning variables by considering wide ranges like Casson parameter (0.1 <= beta <= 10), Rayleigh number (10(4) <= Ra <= 10(7)), Hartmann number (20 <= Ha <= 80) and Lewis number (0.1 <= Le <= 10) on velocity, isothermal and isoconcentration fields are visualized through graphs and tables. Visualization about kinetic energy along with heat and mass transfer rates are disclosed through graphs and tables.Funding The work of U.F.-G. was supported by the Government of the Basque Country for the ELKARTEK21/10KK-2021/00014 and ELKARTEK22/85 research programs, respectively

The Effect of Variable Magnetic Field on Viscous Fluid between 3-D Rotatory Vertical Squeezing Plates: A Computational Investigation

In this paper, the 3-D squeezing flow of viscous incompressible fluid between two parallel plates rotating at the same rate is investigated. The flow is observed under the influence of the varying magnetic field. The flow phenomena are modeled by utilizing the basic governing equations, i.e., equation of continuity, coupled Navier Stokes, and Magnetic Field equations. Using appropriate similarity transformations, the resultant partial differential equations are then transformed into a system of ordinary differential equations. The computational technique is developed via the Homotopy Analysis Method (HAM) to obtain the solution of transformed systems of ordinary differential equations. The influence of several engineering fluid parameters, such as squeeze Reynolds number, magnetic field strength parameter, and magnetic Reynolds number, on velocity and magnetic field components, are observed from different graphs. It has been investigated that by increasing the squeeze Reynolds number, fluid velocity in the y and z directions will be increased as well. On the magnetic field component along the y-axis, an increasing influence of squeezing Reynolds number is also noticed. Similarly, raising the magnetic Reynolds number increases the velocity along the y-axis, whereas the inverse relationship is found for magnetic field components. Furthermore, for each flow phenomenon, an error analysis is also presented.The work of U.F.-G. was supported by the government of the Basque Country for the ELKARTEK21/10 KK-2021/00014 and ELKARTEK20/78 KK-2020/00114 research programs, respectively

Mixed convection of thermomicropolar AgNPs-GrNPs nanofluid: An application of mass-based hybrid nanofluid model

Here, a mass-based hybridity model is applied to inquire about the mixed convection of a thermomicropolar binary nanofluid (TMBNF) upon a shrinking and porous plate. The nanoparticles are the silver (AgNPs) and the graphene (GrNPs), in a spherical shape, suspended in an aqua base fluid. The applied methodology considers the masses of base fluid and nanoparticles as an alternative to the first and second nanoparticles volume fraction, according to the single-phase approach named the Tiwari-Das model. By using the similarity transformation technique, the dominating PDEs are changed to a system of ODEs that can be solved numerically by the bvp4c pattern of Matlab. To validate the numerical method, a comparison is implemented for the heat transfer, the shear stress, and the gradient of microrotation values, with results reported previously that consequently a supreme agreement is observed. The variations of the angular velocity, velocity, temperature distribution, gradient of microrotation, shear stress, and the heat transfer of the TMBNF with the prominent parameters are presented and analyzed by the tabular and graphical results. The originality of this work is related to the use of the mass-based model for TMBNF flow and the derivation of a new configuration of governing equations. It is concluded that the mass-based model with its significant benefits can be utilized successfully with tremendous assurance to abundant theoretical problems of micropolar binary nanofluid flow and heat transfer. New models for the nanofluid hybridity can undoubtedly be quite helpful in the many fields where cooling technologies are essential.The work of U⋅F.-G. was supported by the government of the Basque Country for the ELKARTEK21/10 KK-2021/00014 and ELKARTEK22/85 research programs, respectively

Numerical Simulation of a Time-Dependent Electroviscous and Hybrid Nanofluid with Darcy-Forchheimer Effect between Squeezing Plates

In this article, the behavior of transient electroviscous fluid flow is investigated through squeezing plates containing hybrid nanoparticles. A hybrid nanofluid MoS2+Au/C2H6O2−H2O was formulated by dissolving the components of an inorganic substance such as molybdenum disulfide (MoS2) and gold (Au) in a base fluid of ethylene glycol/water. This hybrid non-liquid flow was modeled by various nonlinear mathematical fluid flow models and subsequently solved by numerical as well as analytical methods. For the numerical solution of nonlinear ODEs, a built-in function BVP4C was used in MATLAB, and the same problem was solved in MATHEMATICA by HAM. The result of the present problem related to the results obtained from the existing literature under certain conditions. The outcomes revealed that the concentration profiles were more sensitive to homogeneity diversity parameters. The simulation of the various physical parameters of the model indicated that the heat transfer through a mixture of hybrid nanofluids was greater than a simple nanofluid. In addition, the phenomenon of mixed convection was considered to improve the velocity of simple nanofluids and hybrid nanofluids, when both cases have low permeability. A rise in the volume fraction of the nanomaterials, Φ, was associated with an increase in the heat transfer rate. It was observed that the heat transfer rate of the hybrid nanofluids MoS2+Au/C2H6O2−H2O was higher than that of the single nanofluids MoS2/C2H6O2−H2O.We acknowledge the insightful comments of the editorial board to improve this work. We also acknowledge the financial support provided by the Postdoctoral research support fund of the School of Mathematical Sciences, Jiangsu University, Zhenjiang, China. The work of U.F.-G. was supported by the government of the Basque Country for the ELKARTEK21/10 KK-2021/00014 and ELKARTEK20/78 KK-2020/00114 research programs