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.
