IGM Colloquium: Avian Flight, Turbulence and Pressure from PIV
Roeland de Kat obtained his engineering degree and doctorate in the Aerodynamics group at Aerospace Engineering, Delft University of Technology. He joined the University of Southampton to work on turbulent shear flows as a research fellow (May 2011 – April 2014). Roeland held the prestigious Leverhulme Trust Early Career Fellowship (May 2014 – April 2017) researching “Feathers on the wing”. Currently he is a New Frontiers Fellow and develops and improves advanced flow diagnostic tools to further our understanding of feathered flight and engineering problems.
Avian Flight and Turbulence
Swifts are among the most aerodynamically refined gliding birds (Lentink et al. 2007). However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size (Lentink and de Kat 2014) and are therefore expected to produce turbulent flow over them. To understand why the swift does not rely on smooth wings, we performed experiments on preserved wings and physical models in a low-turbulence wind tunnel (Lentink and de Kat 2014) and on 3D-printed models in a water tunnel (van Bokhorst et al. 2015). Both listening tube and high-resolution particle image velocimetry measurements showed that the flow over rough wings can be laminar. And comparison with smooth model wings showed that the rough wings aerodynamically equaled or outperformed the smooth wings.
Turbulence and Pressure from PIV
Pressure is a key variable of interest in fluid mechanics. However, measurement of this quantity has been limited to point and surface measurements and alternative methods are needed. Therefore, I have developed several techniques to derive pressure from particle image velocimetry (PIV) data. These techniques were validated on various synthetic flows and applied to different experimental datasets. I will discuss the techniques based on time-resolved stereoscopic-PIV in unsteady (predominantly) 2D flow and time-resolved tomographic-PIV flow in unsteady 3D flow (de Kat & van Oudheusden 2012, de Kat 2012). Using knowledge of the flow itself, these techniques can be simplified and time-resolved stereoscopic-PIV or snapshot tomographic-PIV can be applied to obtain pressure in 3D convective turbulent flows (de Kat & Ganapathisubramani 2013, Laskari et al. 2016, van Gent et al. 2017). If the flow itself is predominantly 2D, one can even determine average pressure and pressure fluctuations from snapshot planar-PIV.
- Lentink D, Muller UK, Stamhuis EJ, de Kat R, et al (2007) How swifts control their glide performance with morphing wings. 446:1082–1085.
- Lentink D, de Kat R (2014) Gliding Swifts Attain Laminar Flow over Rough Wings. PLoS ONE 9:e99901. doi: 10.1371/journal.pone.0099901
- van Bokhorst E, de Kat R, Elsinga GE, Lentink D (2015) Feather roughness reduces flow separation during low Reynolds number glides of swifts. J Exp Biol 218:3179–3191. doi: 10.1242/ jeb.121426
- de Kat R (2012) Instantaneous planar pressure determination from particle image velocimetry. Delft University of Technology
- de Kat R, van Oudheusden BW (2012) Instantaneous planar pressure determination from PIV in turbulent flow. Exp Fluids 52:1089–1106.
- de Kat R, Ganapathisubramani B (2013) Pressure from particle image velocimetry for convective flows: a Taylor’s hypothesis approach. Meas Sci Technol 24:024002.
- Laskari A, de Kat R, Ganapathisubramani B (2016) Full-field pressure from snapshot and time- resolved volumetric PIV. Exp Fluids 57:44.
- van Gent PL, Michaelis D, van Oudheusden BW, et al (2017) Comparative assessment of pressure field reconstructions from particle image velocimetry measurements and Lagrangian particle tracking. Exp Fluids 58:44.