Report on Second Round of Benchmarks

This report summarizes the second round of benchmarks conducted under the NEWA validation strategy. This report is the second of a series of three annual reports on NEWA benchmarks. The first round of microscale benchmarks was directed to developing microscale models that can be driven with mesoscale input forcing, include thermal stratification of the atmospheric boundary layer and high resolution digital models of heterogeneous forest canopy characteristics based on aerial lidar-scan data. These fundamental implementations were developed around the GABLS3 diurnal-cycle and Ryningsnäs forest canopy benchmarks, both in flat terrain conditions. By model intercomparison, NEWA modelers found reasonably good consistency in the simulation of these cases, establishing common understanding of the modeling capabilities of the group before attempting more complex simulation challenges in connection to the NEWA experiments. The first release of the NEWA model chain is produced based on this first round of benchmarks. CFDWind3 is published open-access to engage with early adopters that can help testing and eventually developing new functionalities alongside the NEWA validation plans. The second round of benchmarks has been focused on the following objectives: Validation of flow models from flat to hilly forested terrain: Experimental data from the Rödeser Berg and Hornamossen experiments add terrain complexity to the baseline settings used in GABLS3 and Ryningsnäs. Following the Ryningsnäs approach, a blind test addressing steady-state models was organized around the Rödeser Berg forested hill benchmark. On the other hand, Hornamossen followed the GABLS3 approach to challenge transient models in the simulation of diurnal cycles on an undulated forested landscape. Assessment of annual wind conditions relevant for wind resource assessment and site suitability. The “NEWA Meso-Micro Challenge for Wind Resource Assessment” addresses the evaluation of a hierarchy of methodologies that incorporate mesoscale-to-microscale downscaling to understand the added-value compared to traditional approaches for site assessment that rely only on microscale modeling. This challenge is divided in two phases: the first one in flat terrain and the second one in complex terrain conditions. This report summarizes results for the first phase based on Cabauw and Fino1 sites in onshore and offshore conditions. Development of an open-science benchmarking approach: the benchmarking process established in GABLS3 is rolled out in the next benchmarks to promote a more traceable model evaluation based on sharing of simulation data and evaluation scripts. This report presents benchmark guides for Rödeser Berg, Hornamossen and the NEWA Meso-Micro Challenge and initial results published for the first phase of the Challenge. The third round of benchmarks will exploit experimental data in complex terrain in terms of flow cases targeting the validation of specific modeling features, as well as case studies that integrate these models in wind resource assessment methodologies to assess the impact of those features in terms of relevant quantities of interest for the wind industry (annual energy prediction, site assessment characteristics, mean profiles, etc)