Cambridge Environmental Research Consultants (CERC)

- High Resolution Air Flow Monitoring for Wind Farm Assessments

From

FLOWSTAR-Energy is a practical, high resolution model that simulates air flow and turbulence over flat or complex terrain, including the effects of stratification, variable surface roughness and wind turbines in operation. FLOWSTAR-Energy is an extended version of the FLOWSTAR model of flow over complex terrain; FLOWSTAR-Energy provides the flow field and turbulence output familiar to users of FLOWSTAR and in addition provides a range of essential outputs for wind farm planning, including estimates of free stream, gross and net energy yields. The model simulates wind turbine wakes, their interaction and their effect on the flow field and wind energy resource. FLOWSTAR-Energy can be used at scales from 5 metres up to 60 kilometres.

FLOWSTAR-Energy can model local flow and turbulence using either wind climate data or up to 10 years of hourly meteorological data to provide a map of total energy yields across your flat or hilly site for your choice of wind turbine make and type, enabling you to choose your preferred site.

The following pictures illustrate a few of the type of outputs that are available from FLOWSTAR-Energy, either directly (examples A, B and E) or after simple manipulation of numerical output in a package like Excel (examples C, D and F):

The FLOWSTAR-Energy model of wind turbine wake development exploits similarities between the decay of the wake behind a wind turbine (characterised by a region of reduced wind speed) and the dispersion of a plume of passive gas emitted from an elevated source. FLOWSTAR-Energy has been validated against measured datasets from the Nysted and Noordzee wind farms and from a test turbine at Tjæreborg in Denmark.

The FLOWSTAR model is derived from the theoretical work of Jackson and Hunt, and Hunt et al. The model is based on the premise that different processes dominate the flow dynamics in layers at different heights above the ground; thus in the inner layer shear stress perturbations are locally important and are described by a mixing length closure whilst the flow is also impacted upon by pressure gradients. These are determined from the outer layer flow where stratification plays an important role but where shear stress perturbations have little influence. There is a transitional or middle layer between the inner and outer layer.

Range of Essential Outputs:

  • ‘Flow field output’ provides a 3D estimate of flow and turbulence over the local area at the resolution of your choice and/or at specific locations. Results can either be obtained for each met condition modelled or as an average over the whole period.
  • ‘Potential wind energy output’ provides a map of wind speed and wind energy for the wind turbine make and type of your choice across the local area at the resolution of your choice and/or at specific locations of your choice. Results can either be obtained for each met condition modelled or as average wind speed and total wind energy over the whole period.
  • ‘Wind farm output’ provides free stream, gross and net wind speed, energy yield and capacity factor for individual wind turbines within a wind farm and for the wind farm as a whole. Results can either be obtained for each met condition modelled or as average wind speed and total wind energy over the whole period.
  • ‘Free stream boundary layer profile output’ provides vertical profiles of free stream wind speed, turbulence components and other atmospheric boundary layer characteristics for each met condition modelled.

Easy to Use:

  • An intuitive design and integrated map view make FLOWSTAR-Energy easy to use.
  • FLOWSTAR-Energy is provided with a full digital User Guide providing detailed descriptions of all the model features, as well as worked examples.
  • CERC prides itself on its outstanding support services; the Helpdesk service gives you access to experienced consultants and model developers; training courses are available on request.

Advanced Options:

  • Offshore sites can be modelled using marine parameters to more accurately calculate atmospheric boundary layer parameters over the sea.
  • Measured free stream vertical profiles of wind and turbulence can be used in place of standard FLOWSTAR-Energy profiles.