Flow measurements near the wings and in the wake of a free-flying flapping wing robot using PIV and PTV techniques, with an optical motion tracking system in the loop for robot’s position control. A collaboration of MAVLab and Aerodynamics group of TU Delft.
While flow measurements are typically carried out in a tethered setup, where the flapping wing robot is fixed in the free stream, such setup is never a correct representation of the free-flight condition, which involves not only the correct combination of flapping frequency, free stream velocity and angle of attack, but also their periodic variation induced by the flapping motion. Moreover, the tethering structure itself poses an obstacle for the flow, affecting the flow structures in its vicinity, and often also blocks the view on certain parts of the measurement volume.
During my postdoc at MAVLab, and in collaboration with the Aerodynamics group of TU Delft, we developed a methodology that allows conducting flow measurements around a flapping wing robot in true free flight. The robot flies fully autonomously, following a prescribed path or staying around a fixed point inside a wind tunnel test section. It is controlled by an onboard autopilot (Lisa/S), running Paparazzi UAV software with customized algorithms for a flapping wing vehicle; the position feedback is provided by an optical motion tracking system and is sent to the robot via wireless telemetry.
We have carried out experiments in an open jet wind tunnel as well as using the “ring of fire” approach, where the vehicle follows a closed trajectory passing through the measurement region. Both types of experiments focused on the flight under steady conditions, however, this setup might also be employed for visualizing the flow during maneuvers.
For more details on the control algorithms, employed PIV and PTV techniques, and obtained results please refer to the publications listed below.
Related publications:
- A. D. E. Herrero, M. Percin, M. Karásek, and B. W. van Oudheusden, “Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight,” in 18th International Symposium on Flow Visualization ISFV 18, Zurich, Switzerland, 2018.
[Bibtex]@inproceedings{Herrero2018, address = {Zurich, Switzerland}, author = {Herrero, Alejandro D.E. and Percin, Mustafa and Kar{\'{a}}sek, Mat{\v{e}}j and van Oudheusden, Bas W.}, booktitle = {18th International Symposium on Flow Visualization ISFV 18}, title = {{Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight}}, year = {2018} } - B. {Martínez Gallar}, B. W. van Oudheusden, A. Sciacchitano, and M. Karásek, “Large-Scale Flow Visualization of a Flapping-Wing Micro Air Vehicle,” in 18th International Symposium on Flow Visualization ISFV 18, Zurich, Switzerland, 2018.
[Bibtex]@inproceedings{MartinezGallar2018, address = {Zurich, Switzerland}, author = {{Mart{\'{i}}nez Gallar}, Blanca and van Oudheusden, Bas W. and Sciacchitano, Andrea and Kar{\'{a}}sek, Mat{\v{e}}j}, booktitle = {18th International Symposium on Flow Visualization ISFV 18}, title = {{Large-Scale Flow Visualization of a Flapping-Wing Micro Air Vehicle}}, year = {2018} } - M. Karásek, M. Percin, T. Cunis, B. W. van Oudheusden, C. {De Wagter}, B. D. W. Remes, and G. C. H. E. de Croon, “First free-flight flow visualisation of a flapping-wing robot,” , 2016.
[Bibtex]@article{Karasek2016a, abstract = {Flow visualisations are essential to better understand the unsteady aerodynamics of flapping wing flight. The issues inherent to animal experiments, such as poor controllability and unnatural flapping when tethered, can be avoided by using robotic flyers. Such an approach holds a promise for a more systematic and repeatable methodology for flow visualisation, through a better controlled flight. Such experiments require high precision position control, however, and until now this was not possible due to the challenging flight dynamics and payload restrictions of flapping wing Micro Air Vehicles (FWMAV). Here, we present a new FWMAV-specific control approach that, by employing an external motion tracking system, achieved autonomous wind tunnel flight with a maximum root-mean-square position error of 28 mm at low speeds (0.8 - 1.2 m/s) and 75 mm at high speeds (2 - 2.4 m/s). This allowed the first free-flight flow visualisation experiments to be conducted with an FWMAV. Time-resolved stereoscopic Particle Image Velocimetry (PIV) was used to reconstruct the 3D flow patterns of the FWMAV wake. A good qualitative match was found in comparison to a tethered configuration at similar conditions, suggesting that the obtained free-flight measurements are reliable and meaningful.}, archivePrefix = {arXiv}, arxivId = {1612.07645}, author = {Kar{\'{a}}sek, Mat{\v{e}}j and Percin, Mustafa and Cunis, Torbj{\o}rn and van Oudheusden, Bas W. and {De Wagter}, Christophe and Remes, Bart D. W. and de Croon, Guido C. H. E.}, eprint = {1612.07645}, month = {dec}, title = {{First free-flight flow visualisation of a flapping-wing robot}}, url = {http://arxiv.org/abs/1612.07645}, year = {2016} } - T. Cunis, M. Karásek, and G. C. H. E. de Croon, “Precision Position Control of the DelFly II Flapping-wing Micro Air Vehicle in a Wind-tunnel,” in The International Micro Air Vehicle Conference and Competition 2016 (IMAV 2016), Beijing, China, October 17-21, 2016.
[Bibtex]@inproceedings{Cunis2016, author = {Cunis, Torbj{\o}rn and Kar{\'{a}}sek, Mat{\v{e}}j and de Croon, Guido C. H. E.}, booktitle = {The International Micro Air Vehicle Conference and Competition 2016 (IMAV 2016), Beijing, China, October 17-21}, keywords = {DelFly,MAVLab}, mendeley-tags = {DelFly,MAVLab}, title = {{Precision Position Control of the DelFly II Flapping-wing Micro Air Vehicle in a Wind-tunnel}}, year = {2016} }