Periodic Reporting for period 1 - ESTABLIS-UAS (Exposing Spatio-Temporal structures of turbulence in the Atmospheric Boundary Layer with In-Situ measurements by a fleet of Unmanned Aerial Systems)
Reporting period: 2022-04-01 to 2024-09-30
Sub-mesoscale structures have been identified as important contributors to the energy budget and transport in the atmospheric boundary layer (ABL). The experimental investigation of such structures is challenging, since a large number of spatially distributed measurements are necessary. The challenges are particularly high in the mountain boundary layer (MoBL), where not only convectively-driven organized structures occur, but also three-dimensional shear and local advection become relevant. Improving the understanding of MoBL flow and its parameterization in numerical models has a major impact on the global cycles of water, energy and carbon as 30% of the land surface consists of complex orography. With a concentrated effort and targeted developments, small rotary-wing unmanned aerial systems (UAS) can become game-changing in the sampling of the ABL, when they are applied in coordinated fleets. Three-dimensional measurements of wind, temperature and humidity throughout the full depth of the ABL in most flexible measurement grids can become available. UAS technology has made its way into consumer and industrial applications and is on the verge of becoming an integrated part of civil aviation. The time is now to close observational gaps in the ABL that are increasingly showing with the advancements in numerical modelling towards smaller grid sizes.
The project targets three major challenges:
1. Enable small drones to measure wind, temperature and humidity at high resolution and quantify turbulence parameters. This shall be verified in wind tunnel experiments and validated in field experiments.
2. Develop and optimize the layout of flexible measurement points for distributed measurements with a fleet of drones.
3. Study complex flows in homogeneous and complex terrain to improve the understanding of turbulence and its contribution to ABL dynamics.
The project targets three major challenges:
1. Enable small drones to measure wind, temperature and humidity at high resolution and quantify turbulence parameters. This shall be verified in wind tunnel experiments and validated in field experiments.
2. Develop and optimize the layout of flexible measurement points for distributed measurements with a fleet of drones.
3. Study complex flows in homogeneous and complex terrain to improve the understanding of turbulence and its contribution to ABL dynamics.
Sensor development:
We tested the small drones for turbulence measurements and verified the wind algorithms in the wind tunnel with an active grid at the University of Oldenburg. Multiple scenarios were run to calibrate the drones, test them in discrete gust events and in continuous and repeatable turbulent time series. We tested multiple individual drones to determine the uncertainties between multiple systems of the same type. Multiple configurations were tested with different rotors, weights, and sizes of the drone. The uncertainties were determined to be below 0.3 m/s for wind and a capability to resolve turbulent scales up to 2 Hz. The smallest drone configuration even shows the ability to allow 5 Hz resolution.
We developed fine wire platinum resistance thermometers and tested them in order to measure small-scale temperature fluctuations with the drones and ultimately allow sensible heat flux measurements.
We improved the existing drone configuration to fly 25 minutes and implemented a new drone design that allows up to 70 minutes flight time, which is a breakthrough for observing long time periods with drones.
Fleet operation:
We implemented automatic flight plan generation, including checks for collision-avoidance to improve procedures in the field and adapt flight strategies in the most flexible ways.
We developed and tested multiple flight strategies in the field in two major campaigns, one in mountainous terrain and the other in the DLR WiValdi research wind park. The strategies comprise vertical profiles, horizontal cross-section flights, and distributed hovering flights with up to 20 drones to calculate spatial correlation and coherence.
We developed a virtual measurement framework in synthetic turbulent fields in order to quantify the uncertainty due to the inherent limitations of the drone measurements.
Boundary-layer research:
First test campaigns were performed at the WiValdi research park in Northern Germany and in the Austrian Alps.
At the WiValdi research park, comparisons of spatial measurements with an array of meteorological masts can be analyzed, and measurements downstream of a running wind turbine could be performed, which even showed signatures of tip vortices in the wake. Such signatures have never been measured before with in-situ instrumentation and in full scale in an experiment.
At the Nafingalm site in the Austrian Alps, the flow features in an isolated high altitude valley system could be explored with ground-based and drone measurements. At this site, a major field campaign is planned in 2025 within the TEAMx framework.
We tested the small drones for turbulence measurements and verified the wind algorithms in the wind tunnel with an active grid at the University of Oldenburg. Multiple scenarios were run to calibrate the drones, test them in discrete gust events and in continuous and repeatable turbulent time series. We tested multiple individual drones to determine the uncertainties between multiple systems of the same type. Multiple configurations were tested with different rotors, weights, and sizes of the drone. The uncertainties were determined to be below 0.3 m/s for wind and a capability to resolve turbulent scales up to 2 Hz. The smallest drone configuration even shows the ability to allow 5 Hz resolution.
We developed fine wire platinum resistance thermometers and tested them in order to measure small-scale temperature fluctuations with the drones and ultimately allow sensible heat flux measurements.
We improved the existing drone configuration to fly 25 minutes and implemented a new drone design that allows up to 70 minutes flight time, which is a breakthrough for observing long time periods with drones.
Fleet operation:
We implemented automatic flight plan generation, including checks for collision-avoidance to improve procedures in the field and adapt flight strategies in the most flexible ways.
We developed and tested multiple flight strategies in the field in two major campaigns, one in mountainous terrain and the other in the DLR WiValdi research wind park. The strategies comprise vertical profiles, horizontal cross-section flights, and distributed hovering flights with up to 20 drones to calculate spatial correlation and coherence.
We developed a virtual measurement framework in synthetic turbulent fields in order to quantify the uncertainty due to the inherent limitations of the drone measurements.
Boundary-layer research:
First test campaigns were performed at the WiValdi research park in Northern Germany and in the Austrian Alps.
At the WiValdi research park, comparisons of spatial measurements with an array of meteorological masts can be analyzed, and measurements downstream of a running wind turbine could be performed, which even showed signatures of tip vortices in the wake. Such signatures have never been measured before with in-situ instrumentation and in full scale in an experiment.
At the Nafingalm site in the Austrian Alps, the flow features in an isolated high altitude valley system could be explored with ground-based and drone measurements. At this site, a major field campaign is planned in 2025 within the TEAMx framework.
After the energy crisis due to the war in Ukraine, we have promoted the possibilities with the UAS fleet to measure turbulence in the inflow and wake of wind turbines more offensively. Increasing wind energy production in Germany has become an even more important political goal after 2022. The fleet strategies were tested in close proximity to a wind turbine in order to observe turbulence in the near wake of the turbine. A region where in situ measurements are not possible otherwise. Such measurements can significantly help to improve wake models which are of high importance in site assessment and wind park control to optimise wind park efficiency. Additionally, UAS measurements in the inflow are a cost-efficient tool for power curve measurements and the detection of yaw misalignments (i.e. the yaw angle is not aligned with the incoming wind direction) of wind turbines.
In 2024 first methane measurements were tested with the drone fleet of the ESTABLIS-UAS project in collaboration with the department of atmospheric trace gases of the Institute of Atmospheric Physics. This is a potential new field of application of the methods that are developed in the project and can have great impact on the quantification of green-hous-gas source emissions.
In 2024 first methane measurements were tested with the drone fleet of the ESTABLIS-UAS project in collaboration with the department of atmospheric trace gases of the Institute of Atmospheric Physics. This is a potential new field of application of the methods that are developed in the project and can have great impact on the quantification of green-hous-gas source emissions.