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B01 - Flow over the Hill

Scope

The benchmark is a blind test starting in December 2017. Wind speed profiles on the hill top are provided, vertical (RHI) scans along the axis of 217° as well as profiler data and data from an additional mast are withheld for validation.

Data Accessibility

The benchmark is offered to participants of the NEWA (New European Wind Atlas) project and anyone else interested in participating.

Objectives

Evaluate flow across a forested hill. Evaluate turbulence models in a test site with well-defined boundary conditions. Evaluate also qualitatively the 2D flow across the forested hill.

Input data

The conditions for simulating the Kassel Forested Hill site are:

  • Digitized map of the Rödeser Berg hill with a resolution of 10m.
  • Digitized map of the Forest height on top of the hill with a resolution of 10m.
  • Digitized Plant Area Density with a horizontal resolution of 10m and a vertical resolution of 1m.
  • Digitized Roughness map derived from CORINE data [100m resolution]
  • Wind Speeds/Directions: Measured at M200 (on the hill top) [30 min mean]
  • Obukhov Length: Measured at 60 m at the 200m mast (on the hill top) [30 min mean]
  • Coordinates of wind profilers along the transect line (217°)
  • Gravity g = 9.81 m/s2, Coriolis parameter f=1e-4 s-1
  • Use dry air with a density ρ = 1.225 kg/m3.
  • Mesoscale Tendencies will be provided at a later stage (after the Blind Test)

Validation data

The validation dataset is composed of mean flow and turbulence data from cup and sonic anemometers at two met masts and several lidar profilers along the main transect.  All data are averaged over 30 min.

  • Wind Speed Profiles at two met masts (one upstream, one on top of the hill)
  • Wind Speed Profiles from 3 profiling lidars along the transect
  • 2D field from RHI lidar scans along transect line (217°) through the M200 mast.

The validation dataset includes mean and standard deviation statistics from the ensemble profiles.

Model runs

The atmospheric conditions:

  • Run 1 (Neutral Stratification – 17.11.2016 1120-1150 UTC): WD (MM200 at 188m) = 221.9°,  WD (MM200 at 60m) = 219.7°, WS (MM200 at 188m) = 13.9 m/s, WS (MM200 at 60m) = 9.6 m/s, Obukhov length: ~4000m (MM200 at 60m)
  • Run 2 (Slightly Stable Stratification – 18.11.2016 1600-1630 UTC): WD (MM200 at 188m) = 210.2°, WD (MM200 at 60m) = 196.5°,  WS (MM200 at 188m) = 13.2 m/s, WS (MM200 at 60m) = 7.2 m/s, Obukhov length: ~350m (MM200 at 60m)
  • Run 3 (Stable Stratification – 09.12.2016 0400-0430 UTC):WD (MM200 at 188m) = 248.2°, WD (MM200 at 60m) = 194.5°, WS (MM200 at 188m) = 11.5 m/s, WS (MM200 at 60m) = 8.2 m/s, Obukhov length: ~250m (MM200 at 60m)

or by best fit to the measured inlet profiles (at MM200) if the participant considers that this can improve the results. The computational domain must extend at least to X = ±4000 m in order to include the profilers upstream and downstream of the hill top and make sure that the hill wake is completely covered. The origin of the coordinate system should be placed at MM200 position [UTMX=513590, UTMY=5690182, Zone: 32U] with X pointing East, Y pointing North and Z pointing up.

Output data

The simulated validation profiles consist on vertical profiles at mast and profiler positions of velocity components (U, V, W) and turbulence kinetic energy (tke). In addition, a two-dimensional field along the 217° transect crossing the location of the 200m met mast (MM200) should be provided.

The profiles should have the following order: X(m), Y(m), Z(m), U(m/s), V(m/s), W(m/s), tke(m2/s2).Use the file naming and format convention described in the Windbench user's guide with profID = prof#, where # = [MM140, MM200, WP1, WP3, WP6], i.e. 5 output files per user and model run. Please provide profile data from bottom to top of the modelled domain.

Additionally, please provide the 2D fields (streamwise-vertical) field that is centred around the 200m mast, along the 217° transect, i.e. negative values indicate values towards the southwest, positive values towards the northeast and thus the wake of the hill. This field must be exactly along 217°, independent of the exact inflow wind direction.

Please provide the field as ASCII-file with the following order: Dist(m),Z(m),U(m/s), V(m/s), W(m/s), tke(m2/s2), where Dist is the distance from MM200 and Z(m) and Z is the height above terrain, or as a in a netCDF file. Please provide the field up to a height of at least 800m above terrain.

Please uplad your data compressed in the following shared folder: https://b2drop.eudat.eu/s/cW934bziCPpwKUH

(only upload is alowed, your data is only shared with the benchmark manager)

Remarks

There are no guidelines on the definition of the computational mesh and also on how to model the forests. Please describe in detail if and how you have modelled the forest. Please also comment on how you integrate grid dependency in the evaluation process. You can find other background documentation here.

All input data is stored in the following shared (B2Drop) folder: https://b2drop.eudat.eu/s/NPXl0rxWL6fHd0A

Timeline

  • Submit your simulation results until February, 16th, 2018 
  • The results will be discussed at NEWA's 3rd annual meeting in Oldenburg, 12-16 March 2018

Terms and Conditions

The benchmark is offered to participants of the NEWA (New European Wind Atlas) project and anyone else interested in participating.