Computational fluid dynamic (CFD) numerical simulations are providing alternative to experimental methods in preliminary analysis of aerodynamic behavior for large wind turbines. Shortcomings inherent by experimental methods have popularized the three dimensional CFD methods. This paper, therefore, presents a numerical analysis for NREL 5MW wind turbine rotor using a single moving reference frame approach. ANSYS Fluent is employed to model airflow over the blade's surfaces using Reynolds average Navier-Stokes equations. A steady-state incompressible pressure based solver is applied in form of absolute velocity formulation. Four turbulence models are used: k − SST, k − RNG, k − realizable and Spalart Allmaras to determine the aerodynamic torque. Mesh independence study and validation is also performed. In addition, the predicted flap-wise bending load and comparison of pressure distribution for the four turbulence models are evaluated at different sections of the blade. Due to absence of experimental data for employed blade model, the obtained aerodynamic torque was compared with other reliable numerical simulation results.
IntroductionAntiretroviral therapy plays a major role in reducing the impact of Human Immunodeficiency Virus/Acquired Immune Disease Syndrome, especially in resource-limited settings. However, without proper infrastructure, it has resulted in emergence of drug resistance mutations in infected populations. To determine drug resistance mutations among patients attending a comprehensive care facility in Nairobi, 65 blood samples were successfully sequenced.MethodsWhole blood samples were also tested for CD4+T-cell count and plasma HIV-1 RNA Viral load. Drug-resistance testing targeting the HIV-1 RT gene was determined. Patients were on first line ART that consisted of two NRTIs, and one NNRTI.ResultsFemales were younger (mean 42) than males (mean 45) and lower median CD4+ counts (139 cells/μl) than males (152 cells/μl). The prevalence of drug resistance mutations (any major mutation) in this population was 23.1% (15/65). Major NRTI mutations were detected in 11 patient samples, which included M184V (n = 6), M41L (n=3), D67N (n=2), K219Q (n=3) and T215F (n=2). Major NNRTI mutations were detected in 14 patient samples. They included K103N (n = 10), G190A (n = 1), Y181C (n = 1) and Y188L (n = 1).ConclusionPresence of major mutations in this study calls for proper laboratory infrastructure to monitor treatment as well as regular appraisals of available regimens.
The purpose of present study is to approve use of ANSYS software as a tool for wind turbine simulations. Based on workbench platform designmodeler, mechanical mesh and fluent components, the study attempts to reproduce experimental measurements performed on standstill outboard MEXICO blade section in the low speed low turbulence (LTT), a facility at Delft University of Technology. The outboard MEXICO blade section geometry same as the one used in experiments is adopted for numerical simulations. Three set of angle of attack are taken as variable with inlet velocity hold at 35 m/s and fluid flow viscosity at 1.462kgms −2 in every simulation. Steady state pressure based solver is utilized to solve continuity and momentum Navier-Stoke equations with k − ω SST turbulent model taken as closure. Pressure and velocity are decoupled via SIMPLE algorithm and discretization scheme specified to second order upwind for momentum, turbulent kinetic energy and dissipation rate, while pressure interpolation scheme settled to second order. Computed pressure coefficient around selected airfoil sections is compared to experiment measurements which include; RISOE_121 at 60%R and NACA64418 at 92%R. Comparison shows good agreement between the CFD simulation and experiment results, but slight variation is observed at around RISOE_121 airfoil.
The paper presents overview of source loads and aerodynamic techniques that are feasible for fatigue load reduction on large horizontal axis wind turbines. The article highlights the effects of increasing wind turbine rotor diameter on fatigue load, and feasible aerodynamic techniques that can be employed to reduce fatigue load. Increased in fatigue load is critical as current and future horizontal wind turbines are designed of large rotor blades. Increase in size of wind turbines has been elicited by highly demand for clean energy nowadays as well as need to decrease the cost of energy per kilo watt. As the rotor diameter increases in size, so do effects of air loads acting on the blades. The pitch control systems installed with a purpose of controlling such effects are approaching their capability limits. They are unable to dump sudden, high varying air loads associated with fluctuating wind speed on time. As these effects occur repeatedly during operation of wind turbines, they can cause premature failure or permanent damage of major components due to fatigue load accumulation. In overall, the service life of wind turbine can drastically reduce or high operational and maintenance costs are likely to rise up due to frequent downfalls of unplanned maintenance schedules. Therefore, alternative methods rather than pitch control are reviewed that can improve wind turbines efficiency. The paper concludes by analyzing possible opportunities in future.
The effects associated with the tilted blade tip section on power production and bending load are presented in this study. The blade tip's section of 0.045R size was inclined to the pressure and suction sides for cant angles within a range of -45° to +45°. National Renewable Energy Laboratory (NREL) 5MW wind turbine blade was used as a reference blade. The numerical computations were performed using the finite volume method through ANSYS Fluent version 19.1. First, the aerodynamic performance of different configurations was examined based on computation results of axial force, aerodynamic torque and bending load on flap-wise direction. The best performing blade configuration was selected for further investigations on pitch angle sensitivity for varying wind speed between rated wind speed and cut-out wind speed. A steady-state pressure based solver utilizing Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm was used to solve Reynolds Average Navier-Stoke (RANS) equations closed with Shear Stress Transport (SST) turbulence model. All blades with winglets increase aerodynamic torque. The winglets inclined to the suction side result in a higher increase of aerodynamic torque than the corresponding winglets tilted to the pressure side. The winglet tilted by a cant angle of 15° produced the highest aerodynamic torque increment by about 10% as compared to other blades with winglets. A similar performance trend was observed for the blade with and without winglet when the pitch angle was varied according to the specified wind speed. The general conclusion was made that a winglet can be used to enhance power extraction without the necessity to increase the rotor diameter.
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