Aeromechanical Analysis of a Complete Wind Turbine Using Nonlinear Frequency Domain Solution Method

Abstract

The high-fidelity computational fluid dynamics (CFD) simulations of a complete wind turbine model usually require significant computational resources. It will require much more resources if the fluid-structure interactions between the blade and the flow are considered, and it has been the major challenge in the industry. The aeromechanical analysis of a complete wind turbine model using a high-fidelity CFD method is discussed in this paper. The distinctiveness of this paper is the application of the nonlinear frequency domain solution method to analyse the forced response and flutter instability of the blade as well as to investigate the unsteady flow field across the wind turbine rotor and the tower. This method also enables the aeromechanical simulations of wind turbines for various inter blade phase angles in a combination with a phase shift solution method. Extensive validations of the nonlinear frequency domain solution method against the conventional time domain solution method reveal that the proposed frequency domain solution method can reduce the computational cost by one to two orders of magnitude.

High-fidelity CFD simulations of two wind turbines in arrays using nonlinear frequency domain solution method

“…A central scheme is used for the spatial discretization and a four-stage explicit Runge-Kutta scheme is used for the temporal discretization. Detailed formulation and implementation of the frequency domain solution method can be found in [43][44][45][46].…”

“…where Ω is the volume, S is the surface, U is the vector of the conservative variables, ST is the source term, and 𝐹 ⃗ and 𝐹 ⃗ are the inviscid and viscous flux vectors, respectively. Spalart-Allmaras turbulence model is employed in this work and the above equation can be simply written in a semi-discrete form as [43][44][45][46]:…”

“…For the periodic boundaries of the rotor, the direct periodic (repeating) condition is applied for the time domain method whereas only a single passage domain is required for the frequency domain solution method. With the frequency domain method, the harmonic components are phase-shifted between the periodic boundaries by a given Inter Blade Phase Angle (IBPA), σ, defined by the number of blades available in a rotor, and it is expressed in the following equations where the subscript 1 and 2 are corresponding to the referenced passage and its neighbouring one, respectively [43][44][45][46].…”

“…It can be seen that the present numerical results at different span sections are in good agreement with the experiment and the reference simulation. More details and comparison of pressure coefficients at other blade sections can be found in [43,44]. Therefore, the employed CFD model is accurate enough to predict pressure distributions on the blade surfaces.…”

“…It appears that the inflow wake influences the flow field around the wind turbine, and it has an impact on both the aerodynamics and aeroelasticity of the wind turbine blade. They later extended their study to carry out an aeromechanical analysis of a complete wind turbine model, including a tower using a nonlinear frequency domain solution method [44]. Rahmati et al [45] developed a nonlinear frequency domain solution method for the aeroelasticity analysis of multiple blade row configurations.…”