Dynamic Wake

The Blade Element Momentum Method is fundamentally a steady flow model. The dynamic wake model introduces a lagged response in induction to changes in operating conditions. The dynamic wake model is applied independently to each annulus of the rotor.

The following dynamic wake modelling options are given:

• Dynamic wake base:

  • Annulus: dynamic wake is calculated over the entire annular ring. Induced velocities are averaged over the number of blades.

  • Blade element: The annulus is divided into segments to which separate dynamic wakes are applied.

• Dynamic wake model:

  • Øye: The Øye dynamic wake model captures the lag in induction in response to a change of inflow conditions. This is the recommended default model for dynamic simulation, including a larger time constant for the induction lag, yielding slower wake recovery. It is the most accurate model for linearisation and time domain. But it can increase the computational cost of linearisation calculations as it introduces extra states.

  • Free flow: This model will switch off the induction calculation. The lift, drag and moment polars are used directly. This can be appropriate for use in parked / idling cases. Not recommended for cases where the turbine is operational.

  • Pitt & Peters: The Pitt & Peters dynamic inflow model is equivalent to the pre-4.8 versions of Bladed. This wake model produces a quicker lag recovery and so is not recommended for simulating wind turbines. This option should be used for testing purposes only.

  • Equilibrium: The equilibrium wake model instantaneously updates the induction in response to changes in operating conditions. This represents the steady-state solution. Not recommended for either dynamic or linearisation simulations as it would represent an instantaneous response of the wake, where in reality the response is significantly lagged. This model can be used only to check the steady state (quasi-steady) response. It is appropriate for testing the turbine response under a steady inflow with constant wind shear. This option should be used for testing purposes only.

  • Frozen: Uses the equilibrium induction velocities computed during initial conditions for the entire simulation. Not recommended for dynamic simulation as any perturbation to the steady state solution will result in incorrect induction values. However, this is recommended for linearisation calculations as the lack of response to change in induction can be a good approximation to the lagged dynamic wake response.

• Dynamic tangential induction: For the Øye dynamic wake model, when disabled, the tangential induction will be solved by iteration on each time step, as per the Pitt & Peters model.

Last updated 25-09-2024