| 1. |
- Arnqvist, Johan, 1985-, et al.
(författare)
-
Investigation of Turbulence Accuracy When Modeling Wind in Realistic Forests Using LES
- 2019
-
Ingår i: Progress In Turbulence Viii. - Cham : SPRINGER INTERNATIONAL PUBLISHING AG. - 9783030221966 - 9783030221959 ; , s. 291-296
-
Konferensbidrag (refereegranskat)abstract
- This study presents an evaluation of wind field simulations, in neutral atmospheric conditions, above a heterogeneous forest. The calculations were performed with Large-Eddy Simulation (LES) code OpenFOAM, with explicit modelling of the forest through drag coefficient and forest density. The findings indicate that a large modelling domain is needed in order to reproduce the measurements in different wind directions, since the effect of far upwind forest characteristics influence the wind and turbulence profiles. It is further shown that even though the low resolution of the LES simulations lead to slightly misrepresented single point turbulence characteristics, two point turbulence characteristics are well predicted due to spatial filtering of the small scales.
|
|
| 2. |
- Avila, M., et al.
(författare)
-
Daily cycle simulations of thermally stratified flows over forests
- 2019
-
Ingår i: Wake Conference 2019 22–24 May 2019, Visby, Sweden. - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)abstract
- The aim of the present work is to obtain a better understanding of how to model the thermally stratified wind field over a forest during full diurnal cycles. The setup of the study assumes a horizontally homogeneous forest, with the objective of finding a simple and efficient way to model the canopy flow using time-dependent input data, obtained from measurements and mesoscale simulations. With this, new insights can be gained for future microscale modelling of complex forested terrains using mesoscale input data. In terrain without forest a diurnal cycle is commonly simulated by imposing time-dependent ground temperature. However, the presence of forests partially isolates the temperature at ground level from the flow above the canopy, making this common approach ineffective. This work proposes imposing the time-dependent net radiation at the forest canopy top to drive the thermal stratification changes along the diurnal cycle. To this end, several full days of simulation are driven by prescribing the net radiative heat flux balance measured on top of the canopy, together with a geostrophic pressure gradient. The advantage of the method is its simplicity and that the input data can be easily obtained from mesoscale modelling. When compared to the observations at the Swedish site Ryningsnas, the new method dramatically improves estimations of wind speed, wind direction and turbulent kinetic energy compared to simulations that only assume neutral stratification. Out of the variables studied, temperature and turbulent heat flux profiles were the ones that qualitatively followed the measurements the best, while wind speed and turbulent kinetic energy showed a larger disagreement.
|
|
| 3. |
- Olivares-Espinosa, Hugo, et al.
(författare)
-
Assessment of wind fields over forested sites with LES and a nacelle lidar
- 2019
-
Ingår i: Wake conference. - : IOP Publishing.
-
Konferensbidrag (refereegranskat)abstract
- The capability of a model based on Large-Eddy Simulations (LES) to reproduce turbulence measurements over a forest of heterogeneous density is assessed. Measurements are obtained from an experimental campaign with a continuous wave lidar mounted on the nacelle of a wind turbine (not considered in this work) that scans over a cone in the upstream direction. The measurements are then compared with the results of the LES of the atmospheric boundary layer in neutral stability conditions. The model comprises a full description of the forest over a large area upstream of the lidar by using plant area density data obtained with airborne laser scans, which also provides the terrain elevation. Although the relatively restricted mesh refinement of the LES leads to a limited representation of turbulence towards higher frequencies, comparisons with the measurements show that the model is capable of reproducing the turbulence levels and spatial coherence in the hypothetical rotor plane. Results permit to conclude that the LES-based model is a suitable tool to identify and predict the microscale effects that terrain features have in the wind resource for sites of high complexity. This work exemplifies the challenges associated to the process and interpretation of data from the employed lidar and its setup, for which a filtering technique potentially useful in future studies is presented.
|
|
| 4. |
- Svensson, Nina, 1988-, et al.
(författare)
-
Measurements and Modelling of Offshore Wind Profiles in a Semi-Enclosed Sea
- 2019
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 10:4
-
Tidskriftsartikel (refereegranskat)abstract
- A conically scanning, continuous-wave LIDAR is placed on an island in the central Baltic Sea with large open-water fetch, providing wind and turbulence profiles up to 300 m height. LIDAR and Weather Research and Forecasting (WRF) profiles from one year are used to characterize the marine boundary layer, at the same time performing an evaluation of the WRF model against LIDAR measurements with a focus on low-level jet representation. A good agreement is found between the average wind speed profile in WRF and LIDAR, with the largest bias occurring during stable conditions. The LLJ frequency is highest in May with frequency of occurrence ranging between 18% and 27% depending on the method of detection. Most of the LLJs occur during nighttime, indicating that most of them do not have local origin. For cases with simultaneous LLJs in both data sets the WRF agrees well with the LIDAR. In many cases, however, the LLJ is misplaced in time or space in the WRF simulations compared to the LIDAR. This shows that models still must be improved to capture mesoscale effects in the coastal zone.
|
|
