A numerical study of power performance losses due to ice accretion on a large horizontal axis wind turbine blade has been carried out using computational fluid dynamics (CFD) and blade element momentum (BEM) calculations for rime ice conditions. The computed aerodynamic coefficients for the normal and iced blades from the CFD calculations were used together with the BEM method to calculate the torque, power and C p curves of the wind turbine for both normal and icing conditions. The results are compared with the published data. It is shown that icing results in a reduced power production from the turbine and that changing the turbine controller could improve the power production with iced blades. Copyright

No abstract

CFD-DEM (Computational Fluid Dynamics-Discrete Element Modelling) is a twophase flow numerical modelling technique, where the Eulerian method is used for the fluid and the Lagrangian method for the particles. The two phases are coupled by a fluid-particle interaction force (i.e. drag force) which is computed using a correlation. In a two-phase flow, one critical parameter is the voidage (or void fraction), which is defined as the ratio of the volume occupied by the fluid to the total volume. In a CFD-DEM simulation the local voidage is computed by calculating the volume of particles in a given fluid cell. For spherical particles, this computation is difficult when a particle is on the boundary of fluid cells. In this case, it is usual to compute the volume of a particle in a fluid cell approximately. One such approximation divides the volume of a particle into each cell in the same ratio as an equivalent cube of width equal to the particle diameter. Whilst this approach is computationally straight forward, the approximation introduces an error in the voidage computation. Here we estimate the error by comparing the approximate volume calculation with an exact (numerical) computation of the volume of a particle in a fluid cell. The results show that the error varies with the position of the particle relative to the cell boundary. A new approach is suggested which limits the error to less than 2.5 %, without significantly increasing the computational complexity.

A numerical study of rime ice accretion and resultant flow field characteristics of blade profiles for four different fixed speed, stall controlled wind turbines was performed. Analyses were carried out at Reynolds numbers ranging from of 2.5 × 106 to 5.5 × 106, corresponding to the operational wind speeds and angles of attack ranging from −10 degree to + 20 degree. Numerical analyses showed that an increase in blade profile size reduces the dry rime ice accretion at leading edge, both in terms of local mass and ice thickness. A significant change in the flow behaviour and aerodynamic characteristics is observed, when a comparison is made between plain and iced blade profiles. Results showed an increase in both lift and drag coefficients of wind turbine blade profiles with the leading edge ice.

No abstract