The aerodynamics of a wind turbine is governed by the flow
around the rotor, where the prediction of air loads on rotor
blades in different operational conditions and its relation to rotor structural dynamics is crucial for design purposes. One of the most important challenges in wind turbine aerodynamics is therefore to accurately predict the forces on the blade, where the blade and wake are modeled by different approaches such as the Blade Element Momentum (BEM) theory, the vortex method and Computational Fluid Dynamics (CFD).
A free vortex wake method, based on the potential, inviscid
and irrotational flow, is developed to study the aerodynamic
loads. The results are compared with the BEM method,
the GENUVP code and CFD.

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Development of Free Vortex Wake Method for Aerodynamic Loads on Rotor Blades

This thesis is concerned with the development of a theory for determining the aerodynamic forces for unsteady, compressible subsonic
flow on a propeller and helicopter rotor. The acceleration potential
method was used in developing the basic equations and the method has
been programmed for the propeller on a computer and some results are
given. The integral equations was solved by the doublet-lattice method,
which consists of placing "load" lines at certain locations on the
chord and satisfying the down-vash condition at other selected positions.
The examples presented include the spanvise and chordwise loading
on a rotating propeller for incompressible flow, an example of compressible
flow calculations and finally, a calculation illustrating the loss
of aerodynamic damping of a propeller blade due to the passage of the
blade over its own wake.

Unsteady lifting surface theory applied to a propeller and helicopter rotor

Wind power is currently one of the cleanest and widely distributed renewable energy sources serving as an alternative to fossil fuel generated electricity. Exponential growth of wind turbines all around the world makes it apt for different research disciplines. The aerodynamics of a wind turbine is governed by the flow around the rotor, where the prediction of air loads on rotor blades in different operational conditions and its relation to rotor structural dynamics is crucial for design, development and optimization purposes. This leads us to focus on high-fidelity modeling of the rotor and wake aerodynamics. There are different methods for modeling the aerodynamics of a wind turbine with different levels of complexity and accuracy, such as the Blade Element Momentum (BEM) theory, Vortex method and Computational Fluid Dynamics (CFD). Historically, the vortex method has been widely used for aerodynamic analysis of airfoils and aircrafts. Generally, it may stand between the CFD and BEM methods in terms of the reliability, accuracy and computational efficiency. In the present work, a free vortex filament method for wind turbine aerodynamics was developed. Among different approaches for modeling the
blade (e.g. a lifting line or a lifting surface) and wake (e.g. a prescribed or a free wake model), the Vortex Lattice Free Wake (VLFW) model known as the most accurate and computationally expensive vortex method was implemented. Because of the less restrictive assumptions, it could be used for unsteady load calculations, especially for time-varying flow environment which are classified according to the atmospheric conditions, e.g. wind shear and turbulent inflow together with the turbine structure such as yaw misalignment, rotor tilt and blade elastic deformation. In addition to the standard potential method
for aerodynamic load calculation using the VLFW method, two additional methods, namely the 2D static airfoil data model and the dynamic stall model were implemented to increase capability of the free vortex wake method to predict viscous phenomena such as drag and separation using tabulated airfoil data. The implemented VLFW method
was validated against the BEM and CFD methods, the GENUVP code by National Technical University of Athens (NTUA), Hono turbine measurement data and MEXICO wind tunnel measurements. The results showed that the VLFW model might be used as a suitable engineering method for wind turbine’s aerodynamics covering a broad range of operating conditions.

/pdf/development-of-vortex-filament-method-for-wind-power-3ptfxbm39t.pdf

Development of Vortex Filament Method for Wind Power Aerodynamics

Dynamic Modeling in Engineering

: The report presents a theoretical method which allows the prediction of performance and stress characteristics of a single VTOL-type of propeller- wing-nacelle combination operating in various flight conditions from hovering through transition and into axial flight. The method includes (1) the effects of a distorted wake, i. e., the effects of contraction and radial and axial velocity variations; (2) the effects of hovering close to the ground; (3) the interference effects from a nacelle and wing buried in the propeller slipstream. Also presented are experimental thrust and torque data. However, because of the insufficient accuracy of the experimental data collected, no definite evaluation of the model is made.

/pdf/development-of-a-method-for-predicting-the-performance-and-1vnaq7wjp2.pdf

Andrew R Trenka

Papers

Development of a method for predicting the performance and stresses of vtol-type propellers