WakeBlaster Release Notes

2.0 – Turbulence Dependency and Stability

Turbulence Dependency

Comparison of previous versions of WakeBlaster against observational data (filtered for neutral conditions) showed that the rate of wake dissipation did not vary strongly enough with variation in turbulence. In this version, with the default calibration parameters, the gradient of this dependency has been increased.

Rotor Integration of Wind Speed

In previous versions of WakeBlaster, the integration of wind speed across the rotor was calculated by multiplying two independent factors: * Wake factor – integrating the waked flow plane (relative to ambient) over the rotor. * Shear factor – an analytical factor based on integrating an exponential ambient shear profile. This factor was 1 if the simulation configuration setting power_capture.shear_REWS_method = UseHubWindSpeed was used.

In this version, a single integration of a combined wind speed profile is performed over the rotor area. The combined wind speed profile is made by multiplying: * The waked flow plane (wind speed relative to ambient). * A logarithmic ambient wind speed profile based on the local turbulence and wind conditions and stability information if available.

Stability Model

A model to account for atmospheric stability has been introduced into WakeBlaster (previous versions assumed neutral conditions, with turbulence intensity as a proxy for stability). Stability effects will be considered in any flow case when: * A measurement is provided with a signal ID including MoninObukhovLength with a value of the Monin-Obukhov length in metres. This property is global for the farm and instance ID of the measurement is irrelevant (but must exist). * In the simulation config, a field of wake_model.eddy_viscosity.stability_model = BusingerDyer is added.

From a modelling perspective, the introduction of stability has two effects: * The vertical component of the eddy viscosity is divided by the non-dimensional wind shear (usually denoted ϕ_m in literature). * The ambient wind speed profile (used for both calculating eddy viscosity and integrating wind speed across the rotor) is now a modified logarithmic profile u(z)∝[ln(z/z_0 )-ψ_m ], where ψ_m is the vertical integral of the non-dimensional wind shear. ϕ_m and ψ_m are given by the Businger-Dyer relationship.