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San Gregorio Freeflow

Scope

Participants of the Wakebench projects are invited to join the benchmark for flow models over topography in neutral conditions. Simulations need to be performed to ensure an exhaustive characterization of the wind on the main directions. Reliability of the models will be investigated using the anemometric measurements from the available met-masts.

Objectives

Produce the best estimate of the flow field in neutral conditions above the San Gregorio Magno site for the 240°, 270° and 30° wind directions.

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench who has signed the NDA attached to the test case guide.

Input data

The following input data are at disposal for simulating San Gregorio Magno flow field in neutral conditions:

  • Coordinates of the mast positions and sensor levels
  • The ASTER digital terrain, as well as the roughness model (winter and summer retrieved from www.dataforwind.com), both resampled on a regular grid (30x30 m) shall be provided to the participants.

Inlet conditions are not provided. The results should be made independent of the profile choice, which is left up to the user, by normalizing with respect to velocity (U0) at reference meteorological mast SNG6, through the speed up ratios.

The grid resolution (fixed or variable) should be clearly declared and dependency on grid should be discussed.

A reasonable target U0 is 10 m/s and turbulence intensity [6, 20] %.

Validation data

Time series of 10min averaged wind speeds and directions shall be provided to participants for two of the four met-masts; this data can be used to check model reliability and to further tune-up boundary conditions in terms of height of the boundary layer.

The wind farm layout and meteorological mast layout will be at participants’ disposal, as well as sectorial wind distributions and mean sectorial wind profiles.

 

The overall validation process will consist on the comparison of experimental and numerical velocity ratio (U/U0)j and the ratio of turbulence intensity (ti/ti0)j with respect to SNG6 meteorological mast.

Model runs

The benchmark is structured in two phases: a blind test without validation data and a subsequent round with validation data, for fine-tuning model settings and improving performances.

  • Run 1: 270° (blind)
  • Run 2: 240° (blind)
  • Run 3: 30° (blind)
  • Run 4: 270° (fine-tuning)
  • Run 5: 240° (fine-tuning)
  • Run 6: 30° (fine-tuning)

Output data

The first goal is to compute gross AEP assessment as a function of wind direction, basing on wind resource assessment campaign data. The cross-validation should be based on 4 met masts and particular attention should be deserved to the computation and comparison of wind speed up between the met masts. It is expected also to integrate wind distribution to obtain overall gross AEP. 

Further, the following output is expected:

  • Vertical profiles from ground level to the top of the domain at SNG1, SNG2, SNG3, SNG5 meteorological mast coordinates.
  • For each output point you should provide: velocity components (U, V, W), turbulence kinetic energy (tke) and eddy viscosity (nu_t). Hence, the required outputs are, in this order: X(m), Y(m), Z(m), U(m/s), V(m/s), W(m/s), tke(m2/s2), nu_t(m2/s).

Use the file naming and format convention described in the Windbench user's guide with profID = prof#, where # = [SNG1, SNG2, SNG3, SNG5], i.e. 4 output files per user and model run.

Remarks

The site is very complex and comparison of results from different model can be very difficult.

The following information should to be specified in order to facilitate the final validation and revisions of results:

  • Turbulence closure
  • Convergence criteria
  • Wall conditions
  • Domain shape

Grid architecture

Terms andConditions

Refer to the San Gregorio Magno Test Case guide for the terms and conditions for using the validation datasets.