Passar para o portugues

Passar para o portugues

Abaixo, segue uma introdução, fiz uma compilação de vários artigos!

Energy is fundamental in the socio-economic development and growth of the world. Renewable energy sources like wind energy is indigenous and can help in reducing the dependency on fossil fuels. Due to the limited supplies of fossil fuel and the fear of global warming, significant efforts have been made in renewable energy research.

Wind is the indirect form of solar energy and is always being replenished by the sun. Wind is caused by differential heating of the earth’s surface by the sun. It has been estimated that roughly 10 million MW of energy are continuously available in the earth’s wind. Wind energy provides a variable and environmental friendly option and national energy security at a time when decreasing global reserves of fossil fuels threatens the long-term sustainability of global economy. Since 1980, advances in aerodynamics, structural dynamics, and ‘‘micrometeorology’’ have contributed to a 5% annual increase in the energy yield of the turbines. Advanced wind turbine must be more efficient, more robust and less costly than current turbines. In the early and mid-1980s, the typical wind turbine size was less than 100kW. By the late 1980s and early 1990s, turbine sizes had increased from 100 to 500kW. Further, in the mid-1990s, the typical size ranged from 750 to 1000kW. And by the late 1990s, the turbine size had gone up to 2500kW. Now turbines are available with capacities up to 3500kW.

Current research techniques are producing stronger, lighter and more efficient blades for the turbines. The annual energy output for turbine has increased enormously and the weights of the turbine and the noise they emit have been halved over the last few years. We can generate more power from wind energy by establishment of more number of wind monitoring stations, selection of wind farm site with suitable wind electric generator, improved maintenance procedure of wind turbine to increase the machine availability, use of high capacity machine, low wind regime turbine, higher tower height, wider swept area of the rotor blade, better aerodynamic and structural design, faster computer-based machining technique, increasing power factor and better policies from Government. Computational fluid dynamics (CFD), as a promising technique in wind engineering research, has attracted growing interest in the past two decades. Compared with the conventional experimental approaches, CFD could provide more details about flow field without any need for complicated control and measurement systems. It also provides an inexpensive solution to performing systematic analyses, such as the parametric studies required for performance optimization of wind turbines. To design a high-efficiency wind turbine, the accurate numerical prediction for the rotor aerodynamics can serve as a quicker and lower-cost alternative as compared to wind tunnel experiments.

Acima, segue uma introdução, fiz uma compilação de vários artigos!

Abaixo, inicia a revisão bibliográfica e logo em seguida a referência bibliográfica de cada artigo revisado!

A class of lower-upper symmetric Gauss-Seidel implicit weighted essentially nonoscillatory (WENO) schemes was developed by Huang et al. (2009) for solving the preconditioned Navier-Stokes equations of primitive variables with Spalart-Allmaras one-equation turbulence model. The computations are performed for the two-dimensional lid driven cavity flow, low subsonic viscous flow over S809 airfoil, three-dimensional low speed viscous flow over 6:1 prolate spheroid, transonic flow over ONERA-M6 wing and hypersonic flow over HB-2 model. The viscous flow over S809 airfoil was considered at moderate angle of attack (AOA). The S809 airfoil was designed specially for horizontal-axis-wind-turbine (HAWT) applications. The thickness ratio of the airfoil is 21%. A 600 mm chord length model of the S809 airfoil has been tested in a 1.8 m x 1.25 m low turbulence wind tunnel (Ghia et al., 1982). Four grid systems of C-type topology are generated for grid-independency testing. The grid points are 185 x 49, 273 x 73, 409 x 109 and 601 x 145 from coarse to fine grid system, and there are 137, 207, 321 and 481 points on airfoil surface, respectively, and the outer boundary for all four grid systems is about 20 chord lengths away from airfoil. The freestream Mach number is 0.001, Reynolds number is 2 x 106 and AOA is 9.22º. For all the cases computed, the solutions of the present algorithms are in very good agreement with the available experimental data.

Huang J.-C, Lin H., and Yang, J.-Y, 2009, “Implicit preconditioned WENO scheme for steady viscous flow computation”. Journal of Computational Physics, Vol. 228, p. 420-438.

Ghia, U., Ghia, K.N., and Shin, C.T., 1982, “High-Re solutions for incompressible flow using the Navier-Stokes equations and a multigrid method”. Journal of Computer Physical, Vol. 48, p. 387-411.

The numerical simulation of horizontal axis wind turbines (HAWTs) with untwisted blade was performed by Thumthae and Chitsomboon (2009) to determine the optimal angle of attack that produces the highest power output. The numerical solution was carried out by solving conservation equations in a rotating reference frame wherein the blades and grids were fixed in relation to the rotating frame. In this study, steady state, incompressible flow is assumed. The blade profile was that of the National Renewable Energy Laboratory´s (NREL) S809 airfoil through out the span with some modifications near the hub to blend with the hub spar. Computational results of the 12º pitch compare favorably with the field experimental data of The National Renewable Laboratory (USA), for both inviscid and turbulent conditions. Numerical experiments were then conducted by varying the pitch angles and the wind speeds. The power outputs reach maximum at pitch angles: 4.12º, 5.28º, 6.66º and 8.76º for the wind speeds 7.2, 8.0, 9.0, and 10.5 m/s, respectively. The optimal angles of attack were then obtained from the data. Under typical design conditions lift to drag ratio was proved theoretically and confirmed by the computation as insignificant design parameter.

Thumthae, C., and Chitsomboon, T., 2009, “Optimal angle of attack for untwisted blade wind turbine”. Renewable Energy, Vol. 34, p. 1279-1284.

In the Yu et al.´s work (2011), firstly, integrated loads predicted by Navier-Stokes solver are compared with those from the lifting surface method with and without Du-Selig stall delay model. Du and Selig (1998) developed a stall delay model designed for use in blade element momentum (BEM) and vortex lattice (VL) methods which is based upon the analysis of 3D integral boundary layer equations to determine the effects of rotation on boundary separation. Then, pressure coefficients at five spanwise locations (r/R = 0.30, 0.47, 0.63, 0.80, 0.95) are compared with the Unsteady Aerodynamics Experiment (UAE) Phase VI (Hand et al., 2001). Surface limiting streamlines on the suction side of the blade are presented to depict the flowseparation and 3D effects. At last, a MATLAB code is developed to extract sectional aerodynamic force coefficients from CFD computations which are then compared with 2D S809 airfoil wind tunnel experimental aerodynamic force coefficients, the corrected data from Du-Selig model, and the result derived from a lifting surface code based on experimental data (Tangler, 2003). The stall delay and augmented lift phenomenon especially at the inboard part of the blade is presented in detail.

Du, Z., and Selig, M., 1998, “A 3-D stall-delay model for horizontal axis wind turbine performance prediction”. American Institute of Aeronautics and Astronautics - AIAA-98e0021 paper, January.

Hand, M.M., Simms, D.A., Fingersh, L.J., Jager, D.W., Cotrell, J.R., Schreck, S., and Larwood, S.M., 2001, “Unsteady aerodynamics experiment phase VI: wind tunnel test configurations and available data campaigns”. National Renewable Energy Laboratory (NREL), NREL/TP-500e29955.

Tangler, J.L., 2003, “Insight into a wind turbine stall and post-stall aerodynamics”. Windpower. Austin, Texas.

Yu, G., Shen, X., Zhu, X., and Du, Z., 2011, “An insight into the separate flow and stall delay for HAWT”. Renewable Energy, Vol. 36, p. 69-76.

In working Niu et al. (2011), a parallel computing technology is applied on the simulation of a wind turbine flow problem. A third-order Roe type flux limited splitting based on a pre-conditioning matrix with an explicit time marching method is used to solve the Navier-Stokes equations. A three-dimensional compressible flow model with a pre-conditioning matrix for a low Mach number flow strategy is used. This work presents the results of two-dimensional and three-dimensional numerical simulation of the flow field around the S809 airfoils which are 21% thick, laminar-flow airfoil designed specifically for horizontal axis wind turbine (HAWT). The original FORTRAN code was parallelized with Message Passing Interface (MPI) language and tested on a 64-CPU IBM SP2 parallel computer. The test results show that a significant reduction of computing time in running the model and a superlinear speed up rate is achieved up to 32 CPUs at IBM SP2 processors. The speed up rate is as high as 49 for using IBM SP2 64 processors. The test shows very promising potential of parallel processing to provide prompt simulation of the current wind turbine problems. Comparisons between the calculated and experimental surface pressure distributions for angles of attack of 0º, 1.02º, 5.13º and 9.22º, respectively, are presented. The Cp comparisons for the selected four angles of attack show reasonably good agreement over the entire airfoil surface, except in the regions of the separation regions when the angle of attack at 5.13º and 9.22º. Since the calculations assume fully turbulent flow, accurate separation capturing is difficult in our simulation. But overall the predictions are satisfactory.

Niu, Y.-Y., Tang, H.-W., Lee, L.-C., and Tseng, T.I., 2011, “Simulation of flowfields induced by wind blades based on a parallelized low-speed flow solver”. Computers & Fluids, Vol. 45, p. 249-253.

Sayed et al. (2012) has presented the results of aerodynamic simulations of the steady low-speed flow past two-dimensional S-series wind-turbine-blade profiles, developed by the National Renewable Energy Laboratory (NREL). The blade profiles used in the simulations are the S-series profiles, namely; S809, S814, S815, S817, S818, S819, S820, S821, S822, S823, S825, S826, S827, S828, S829, S830, S831, S832, S833, S834 and S835. The aerodynamic simulations were performed using a Computational Fluid Dynamics (CFD) method based on the finite-volume approach. The governing equations used in the simulations are the Reynolds-Averaged-Navier-Stokes (RANS) equations. The wind conditions during the simulations were developed from the wind speeds over different sites in Egypt. The lift and drag forces are the most important parameters in studying the wind-turbine performance. It is concluded from the results that; the angle of attack (AOA) has a dominant effect on determining the optimum profile while the wind speed does not affect the optimum profile. The optimum operating AOA should lie between -4º and 3º to get the maximum sliding ratio and the maximum power extracted from the wind. Moreover, it is concluded from the results that the NREL wind turbine profiles S825, S826, S830 and S831 are the most efficient blade profiles and they are suitable for wind turbines working at low and high wind speeds.

Sayed, M.A., Kandil, H.A., and Shaltot, A., 2012, “Aerodynamic analysis of different wind-turbine-blade profiles using finite-volume method”. Energy Conversion and Management, Vol. 64, p. 541-550.

Investigation of the effects of near-wall grid spacing for the SST-K- model and study of the aerodynamic behavior of a horizontal axis wind turbine are the two goals of the Moshfeghi et al. (2012)´s paper. The National Renewable Energy Laboratory (NREL) Phase VI is used as the aerodynamic model. Eight different cases are investigated for the near wall grid spacing study. Furthermore, one case is studied in both the SST-K- and the Langtry-Menter transitional models. For all cases the total number of nodes are fewer than 5,000,000. The results of this paper lead us to a general understanding about the wind turbine blade aerodynamics. Thrust forces, flow patterns and pressure coefficients are compared at different wind speeds. The thrust values of the SST-K- are not in a good agreement with the test results. The streamlines show that the inboard section of the blade has a severe complex 3D flow which separates at low velocities; the mid-span section stays attached for higher velocities and the outboard part has 2D-like behavior and separates as the last part. Besides, it is observed that Gamma-Theta transitional model behaves differently from the SST-K-, especially at the inner part and the results are closer to the test results.

Moshfeghi, M., Song, Y.J., and Xie, Y.H., 2012, "Effects of near-wall grid spacing on SST-K- model using NREL Phase VI horizontal axis wind turbine". Journal of Wind Engineering and Industrial Aerodynamics, Vol. 107-108, p. 94-105.

Gharali and Johnson (2012) fizeram um estudo com o objetivo de to give an overview of the numerical simulation using a commercial CFD package, ANSYS FLUENT® v12.1, as an accurate, time efficient and economic way of simulating an oscillating freestream over a stationary S809 airfoil for different Re and a range of reduced frequencies. This study also shows the lift and drag coefficients for Re = 106 in the static case for the realizable k- and SST k- methods and published experimental as well as numerical data. Results for dynamic stall are compared with prior experimental and semi-empirical pitch oscillating S809 airfoil studies. The behavior of the vorticity fields, wake velocity profiles and aerodynamic coefficients are provided in detail to demonstrate the connection of the results to Re and reduced frequency. These results show that a decreasing lift coefficient depends on the thickness of the erosion rather than the length of the erosion. Erosion of the leading edge changes the standard shape of the airfoil and when significant erosion occurs the characteristics of the dynamic stall phenomena based on the smooth S809 can no longer be predicted. The average (maximum) lift decrease has reached 34% (76%) for the thickest erosion assumption. These lift differences show that under severe erosion, the performance of the wind turbine blade is affected significantly.

Gharali, K., and Johnson, D.A., 2012, “Numerical modeling of an S809 airfoil under dynamic stall, erosion and high reduced frequencies”. Applied Energy, Vol. 93, p. 45-52.

Lee et al. (2012) usaram the Computational Fluid Dynamics (CFD) to evaluate the performance of a blade with blunt airfoil which is adapted at the root. ANSYS FLUENT® software is used of numerical analysis, and ANSYS ICEM CFD® is used for generating mesh representations. The experimental conditions of the blade used for this study were based on experimental data presented by the National Renewable Energy Laboratory (NREL). This blade consists of an S809 airfoil has length L of ̴ 5.03 m long. The models for numerical analysis are blades in which the blunt trailing-edge thickness was 1%, 5% and 10% of the chord. These blades are modifications of the NREL Phase VI blade. For detailed data, the numerical analysis has been performed for wind speeds of 7, 10, 15, 20, and 25 m/s. For numerical analysis, about 4 million grid points were generated and O-type mesh was used to cover the blade. ANSYS ICEM CFD® was selected. For this study, computations were conducted using ANSYS FLUENT®, commercial CFD software package. This software includes well-known RANS equation and various zero-, one-, two-equation turbulent models are available in ANSYS FLUENT®. The Sparalt-Allmaras model was selected as the turbulence model and used throughout the study. Also, the comparison analysis of results of a baseline and modified blades has been performed.

Lee, S.G., Park, S.J., Lee, K.S., and Chung, C., 2012, “Performance prediction of NREL (National Renewable Energy Laboratory) Phase VI blade adopting blunt trailing edge airfoil”. Energy, Vol. 47, p. 47-61.

No trabalho de Mo et al. (2013), the Large-Eddy Simulation (LES) on the turbulent wake characteristics behind National Renewable Energy Laboratory (NREL) Phase VI wind turbine was performed to achieve a better understanding of the wind turbine wake formation and propagation. The computational domain has a height of 24.4 m and a width of 36.6 m, corresponding to NASA-Ames 24.4 m x 36.6 m wind tunnel, with a length of 222.32 m in the stream-wise direction. The wind turbine has a tower height of 11.5 m and is placed approximately in the middle of the wind tunnel at a distance of 2d from the upwind boundary. A uniform velocity condition of 7 m/s with turbulence intensity of 0.2% was applied as the boundary condition at the inlet where the flow enters the computational domain. It should be noted that the uniform velocity profile and the small turbulence intensity considered in this research corresponds to the experiments conducted by the NREL. For the outlet where the flow leaves the domain, the ambient domain condition was selected. The S809 airfoil was used in the construction of the blades. The S809 airfoil is a 21% thick airfoil, for sustained maximum lift, insensitivity to surface roughness, and low profile drag. The reliability and validity of the analysis were verified using the published results of the experiment and an excellent agreement was observed in the comparisons of time-averaged pressure coefficients and power. It was observed that LES showed much better results than the steady-state calculations of the two-equation turbulence models of previous researches.

Mo, J.-O., Choudhry, A., Arjomandi, M., and Lee, Y.-H., 2013, “Large eddy simulation of the wind turbine wake characteristics in the numerical wind tunnel model”. Journal of Wind Engineering and Industrial Aerodynamics, Vol. 112, p. 11-24.

No trabalho de Esfahanian et al. (2013), a study para a mixed CFD (Computational Fluid Dynamics) and Blade Element Momentum Method (BEM) analysis is implemented for simulating the flow field around a wind turbine rotor to predict the aerodynamic performance such as the Power Curve diagram and the forces and moments imposed on the rotor blades that are essential in structure and/or aeroelastic design. The construction of the computational domain and grid generation are performed by the use of Gambit commercial software. The outer boundary of the computational domain is in the form of a cut conical shape in order to construct a C-type mesh for better simulating the wake region after the separation of the flow over the airfoil. The outer boundary is 5 airfoil chord lengths (5c) far from the airfoil leading edge. The base of the conic is10c long which is expanded equally at each side of the trailing edge of the airfoil. Two-dimensional computational mesh is a structured multi-blocks C-type grid, that contained totally 23,625 cells. The present approach requires considerable less computational time and memory than three-dimensional simulation of a wind turbine rotor by merely CFD methods, while retains the desirable accuracy. The Esfahanian´s work consists of two parts: 1 - calculating 2D aerodynamic coefficients of several spanwise sections of the blades by CFD methods, using ANSYS FLUENT® commercial software. 2 - Simulating 3D-flow field through the wind turbine rotor using the BEM technique. In order to model the laminar zone before the transition and the turbulent zones after that, the computational domain is decomposed into three regions by three normal lines to the airfoil surface according to the locations where transition occurs in each side of the blade section. Two-dimensional numerical simulations are performed by use of ANSYS FLUENT® (v6.3) commercial software that uses FiniteVolume Method (FVM) in CFD calculations. A density based, time dependent (unsteady) solver with implicit formulation in both time and space, Green-Gauss cell based gradient approximation and Roe-FDS type of flux calculation is chosen. These simulations are used to construct the lift and drag curves for S809 airfoil. The SST k-ω turbulence of Menter (1994) is used in turbulent zones due to good prediction in separated flow simulation. The model uses the standard k-ω model near the wall, but switches to a k-ε model away from the wall. Second-order upwind discretization is chosen for momentum equations and turbulence equations including specific dissipation rate and turbulent kinetic energy equations are discretized using first-order upwind scheme. For time integration, the first order implicit formulation is used. To validate the current approach, the Combined Experiment Phase II Horizontal Axis Wind Turbine known as United States National Renewable Energy Laboratory (NREL) Phase II Rotor is used. The comparison indicates that the combination of CFD and BEM methods is much faster than merely CFD approaches while accurate enough to be used for engineering purposes. Two-dimensional numerical simulations are performed at 4 different Reynolds number (Re = 0.25 x 106, 0.5 x 106, 1.0 x 106, and 1.5 x 106) in a wide range of angles of attack (AOA) (-5º ≤ AOA ≤ 40º) in steps of one degree.

Menter, F.R., 1994, “Two-equation eddy-viscosity turbulence models for engineering applications”. The American Institute of Aeronautics and Astronautics Journals (AIAA), Vol. 32(8), p. 1598-1605.

Esfahanian, V., SalavatiPour, A., Harsini, I., Haghani, A., Pasandeh, R., Shahbazi, A., and Ahmadi, G., 2013, “Numerical analysis of flow field around NREL Phase II wind turbine by a hybrid CFD/BEM method”. Journal of Wind Engineering and Industrial Aerodynamics, Vol.120, p. 29-36.

A series of two-dimensional unsteady simulations of the ow around the United States National Renewable Energy Laboratory (NREL) S809 airfoil at different angles of attack were performed by Pellegrino and Meskell (2013). The uid domain has been created with the ANSYS® default meshing tool. The domain extends to 10 c (airfoil chord) length from the body in the upstream direction, 40 c in the downstream direction and 20 c in the cross-ow direction. The reference chord length is 1 m. The mesh has approximately 100,000 nodes. Turbulence closure is modeled by the Shear Stress Transport (SST) eddy viscosity model. The airfoil throughout was specied by no-slip conditions. Flow speed has been calculated starting from the Reynolds number value of 106. As propriedades de entrada do escoamento são: velocidade igual a 14.607 m/s, density igual a 1.225 kg/m3 e viscosidade dinâmica igual a 1.7894 x 10-5 kg/(m s). At high angles of attack a wind turbine blade section (NREL S809) will behave primarily as a bluff body causing vortex shedding and hence will experience uctuating loads. The lift force and the pitching moment (calculated with respect to the mid-chord) are dominated by the fundamental vortex shedding frequency, but signicant contributions at the higher harmonics are also present. For the drag the second harmonic is as signicant as the fundamental frequency, with the third and fourth harmonics contributing to a lesser extent. In general, the wake shape is consistent with what is seen in the literature for common bluff bodies, suggesting that the vortex shedding process has been correctly captured.

Pellegrino A., and Meskell, C., 2013, "Vortex shedding from a wind turbine blade section at high angles of attack". Journal of Wind Engineering and Industrial Aerodynamics, Vol. 121, p. 131-137.

No trabalho de Lanzafame et al. (2013), a CFD 3D model was developed to evaluate wind turbine rotor performance and support the 1D BEM code design. Simulations were performed on a Fujitsu Primergy TX200 S5 Server, with 2 Intel Quad Core Xeon X5570 processors (2.93 GHz) and 48 GB of RAM memory installed. The SST k- fully turbulent model was compared to the SST Transitional model simulation results. The RANS SST Transitional model demonstrated superior capabilities, predicting mechanical power with an error less than 6% of experimental data. The local correlation parameters of the Transitional SST model were modied to calibrate it for wind turbine applications. These variables were modied after a signicant number of 2D numerical tests on airfoils (S809, NASA ls421, NACA 4415). To reduce computational time, an ANSYS FLUENT® parallel version was performed. The grid was partitioned using a Metis auto partition method. In this way, the grid was divided into 8 parts each of which had the same computational weight. So, each of the 8 cores solve the Navier-Stokes equations of their own part of the grid. Thus a 60-70% reduction in computational time was obtained. The model was validated by comparing the numerical results of simulations with the experimental data of the National Renewable Energy Laboratory (NREL) PHASE VI wind turbine. The errors between simulated results and experimental data were less than 6% for all simulations. The simulated mechanical power and power coefcient trends are presented in this work. Any differences are due to the use of unrealistic data for the aerodynamic coefcients. The 1D BEM model over-predicts the maximum Cp at a wind speed greater than about 16%.

Lanzafame, R., Mauro, S., and Messina, M., 2013, "Wind turbine CFD modeling using a correlation-based transitional model". Renewable Energy, Vol. 52, p. 31-39.

No trabalho de Lee et al. (2014), the effects of idealized local shear flows around a S809 airfoil, on its aerodynamic characteristics were analyzed by CFD simulations. The local shear flow effect induced by turbulence, however, is not explicitly considered in the popular BEMT-based simulations. Extreme situations can occur in a large-scale wind farm where the inflow field of a wind turbine may contain strong tip vortices generated from upstream turbines. The S809 airfoil dedicated to horizontal-axis wind turbine applications, is used as a test airfoil model. S809 is a laminar airfoil that was designed to achieve a restrained maximum lift. Two-dimensional simulations of an airfoil are conducted with the commercial CFD software, ANSYS FLUENT®. In order to resolve the transition on the surface of the airfoil, the transitional SST k- model is adopted. The second order upwind interpolation method is used for all flow variables. Several simulations are conducted for validation of the analysis method and mesh. The inflow condition is uniform, constant velocity 29.215 m/s, which is equivalent to Reynolds 2 x 106, and the shear rate is zero. Tested cases of the angle of attack (AOA) are 0, 5.13 and 9.22. The mesh also satisfies the condition y+ ~1, which the transient turbulent model requires for accuracy. According to the results, it is observed that the shear rate can cause significant changes in the aerodynamic coefficients, particularly in the lift coefficient, and its magnitude is dependent on the reference velocity and chord length. On the contrary, the angle of attack is not relevant to the lift change caused by shear flow. However, the relative amount of the lift change caused by shear flow compared to the total lift is significantly dependent on the angle of attack. At a small AOA, its relative impact gets greater as the amount of lift generated in the uniform flow component becomes smaller.

Lee, K.S., Chung, C.H., and Baek, J. H., 2014, "Lift correction model for local shear flow effect on wind turbine airfoils". Renewable Energy, Vol. 65, p. 275-280.

Acima, termina a revisão bibliográfica e a referência bibliográfica de cada artigo revisado!