Inclusion of the Structural Velocity Induction

When the turbine structure has a notable amount of movement in axial direction compared to the undisturbed wind speed, the induced velocity computed using formulations in the modelling of flow speed components at an aerofoil section can deviate from the expected results. This characteristic is particularly relevant for floating wind turbines having strong platform motions, or when the turbine is exposed to sudden changes of wind speed and direction (such as gust) which ultimately lead to shut down. To take this effect into account, the axial component of the structural velocity needs to be considered in the induction calculations. Bladed models this by modifying the convection velocity formulation for the mass flux that reads:

\[ \begin{equation} \bscalar{V_m} = \bvector{n^T V_0} + \bvector{V_s \cdot n} + \bscalar{v_n} \end{equation} \]

and when the Glauert correction is active, as described in Glauert, 1926a the convective velocity is modified according to the following formula:

\[ \begin{equation} \bscalar{V_m} = \left| \bvector{V_0} + (\bvector{V_s \cdot n})\bvector{n} + \bscalar{v_n} \bvector{n} \right| \end{equation} \]

Finally, the structural velocity is also used in the calculation of the axial induction factor:

\[ \begin{equation} \bscalar{a} = \bscalar{\dfrac{v_{n}}{V_0 + \bvector{V_s \cdot n}}} \end{equation} \]

This correction term is active by default to ensure more accurate calculation results.

Last updated 30-08-2024