Examensarbeten för masterexamen // Master Theses
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- PostAerodynamic Loads On Rotor Blades(2011) Abedi, Hamidreza; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsIn the last decade, we have heard more and more about the need of renewable clean energy, but not much has been done. Currently, the wind power energy is the most popular of all of these green technologies. Thousands of wind turbines are being invested and installed everywhere worldwide. Thus, many questions arise. The aerodynamic loads on the rotor blades are the largest loads acting on a wind turbine. The horizontal wind turbine types of blades are usually made of two or three airfoils such as a propeller. In these types of blades, it is the lift force which makes the rotor turn. The drag force acts perpendicular to the lift force due to the resistance of the airfoil from the wind and counteracts the rotation to rotor. Therefore, predicting these loads accurately is one of the most important parts of the calculations in wind turbine aerodynamics. Another reason for computing the aerodynamic loads on rotor blades is to model the aeroelastic response of the entire wind turbine construction. There are different methods to calculate the aerodynamic loads on a wind turbine rotor with different level of complexity such as Blade Element Momentum Method (BEM), Vortex Method, Panel Method and Computational Fluid Dynamics (CFD). Most aerodynamic codes use BEM (together with many additions) which is very fast and gives fairly accurate results. The main goal of this project is studying the Helical Vortex Method. In this text, helical vortex method has been developed and compared with Blade-Element Momentum (BEM) theory for the analysis of wind turbine aerodynamics.
- PostBlade Element Momentum Method for a Counter-Rotating Pump-Turbine(2021) Ibanez Uribe, Cristobal; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Nilsson, Håkan; Abedi, HamidrezaBlade Element Momentum (BEM) methods are widely used for initial aerodynamic analysis of wind and tidal turbines, as well as aircraft and marine propellers. Mainly because they use less computational resources and can give fairly accurate results. This thesis studies the applicability of such method for load prediction on the runner blades of a model scale axial shaft-driven Counter-Rotating Pump-Turbine (CRPT). One of the main assumptions and modifications adopted in the BEM method was to omit the axial induction factor, a ,and let the axial velocity be constant. This considering that the volumetric flow rate, q, and cross-sectional area, A, must remain unchanged throughout the turbomachine. Additionally, an attempt to include the constant pressure difference across the rotors as extra loading being exerted on the blade, as well as a suggestion on how to apply the BEM method on the downstream rotor are presented and evaluated. The data needed to implement the BEM method is created by running several CFD simulations using OpenFOAM. These simulations produce 2D aerodynamic airfoil-like characteristics of lift and drag coefficients, Cl and Cd, at different angles of attack (AoA) and Re numbers in both pump and turbine mode for different blade profiles along the radial direction. Furthermore, validation cases at different operating conditions are also simulated with OpenFOAM assuming steady-state flow. This is done for different geometries. One of them considers the turbomachine with both runners operating simultaneously and the other geometries isolate each runner individually. It is concluded that it is possible to use the BEM method with a reasonable amount of error for certain operating conditions. Most importantly the behaviour of the dimensionless thrust and power coefficients, CT and CP at different tip speed ratios, T SR, tends to follow the same trend as CFD. Further work needs to be done in order to fully validate such a method for this type of turbomachine.
- PostCFD modeling of the Neutral Atmospheric Boundary Layer above Inhomogeneous forest(2020) Kleruu, Alfred Andrew; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Davidson, Lars; Abedi, HamidrezaHomogeneous assumption of distribution of forest canopy has been a keen study in several works in assessing the effect of forest canopy on the mean velocity profile and turbulence within a wind farm. While this assumption plays a vital role in wind energy assessment, it doesn’t represent the realistic approach given by the inhomogeneous (heterogeneous) assumption. In this study the Large-Eddy Simulation (LES) is used to model the neutral Atmospheric Boundary Layer (ABL) over a heterogeneous forest wind farm. This is done by utilizing the power of the Computational Fluid Dynamics (CFD) tool, STAR-CCM+ software. Thereafter the structural dynamic response of the wind turbines are assessed using the aero-elastic solver FAST. Comparisons are made between two simulation cases (heterogeneous versus homogeneous forest canopy distribution) and it is seen that the homogeneous forest assumption over-predicts turbulent kinetic energy levels the wind turbines are subjected to compared to the heterogeneous forest assumption.
- PostNeural Network-Guided Active Yaw Control in a Two-Turbine Wind Farm(2022) Alatalo, Viktor; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Davidson, Lars; Abedi, HamidrezaTo optimize the power production of wind farms, the wakes can be manipulated and their adverse effects mitigated. A promising wake deflection method is yaw misalignment. By deflecting the wake away from downwind turbines, the yaw-based approach seeks to increase the collective power production of the grouped wind turbines by sacrificing some power output of the upwind turbine in yaw. Using an artificial neural network (ANN), specifically a feedforward neural network, this work aims to develop an active yaw control (AYC) scheme for a two-turbine wind farm. To aid in the development of the AYC, FAST.Farm is utilized, which is a newly developed midfidelty tool by the National Renewable Energy Laboratory (NREL). FAST.Farm is calibrated by comparing several of its predicted wake properties to results of a Large-Eddy Simulation (LES) for which a 1D actuator disk method is used. Subsequently, with the purpose of gathering data to train an ANN, the wind farm is simulated in a multitude of operating conditions. Specifically, the operating conditions are combinations of various turbulence intensities, wind shear exponents, and yaw angles for the upwind turbine. The ANN is then used to predict total power production in the wind farm, which informs the decisions of the AYC. It is shown that, when the turbulence intensity (TI) is low (5 %), the AYC increases wind farm power production by 5-6 %, depending on the wind shear exponent (a smaller wind shear exponent yields a larger gain in power production). As the TI increases, the gain in power production goes to zero. Moreover, it is shown that the AYC increases the structural loads (up to 20 %) on both the upwind turbine and downwind turbine with respect to the blade root out-of-plane bending moment and tower base fore-aft moment. With respect to the yaw bearing moment, the AYC greatly increases it for the upwind turbine (up to 7 times) and slightly lowers it for the downwind turbine (roughly 5 %).