Dr. Swathi Krishna

Visiting postdoc

École polytechnique fédérale de Lausanne (EPFL)

Dr. Swathi Krishna obtained my MSc. in aerospace engineering from Delft University of Technology (TU Delft), Netherlands and Ph.D. in fluid mechanics from École Polytechnique Fédérale de Lausanne (EPFL), Switzerland. Her research interests are primarily in the field of experimental fluid dynamics. Particularly, she is interested in understanding flow phenomena by characterizing relevant flow features, their organization, and evolution in biologically-inspired fluid problems such as insect flight applicable to micro air vehicles. Following her PhD, she carried out an industrial postdoc, leading a team of six people, in the field of machine learning and augmented reality. She would like to combine my experiences in these fields to provide robust solutions to flow problems, for instance, investigating the response behavior of aerodynamic surfaces to environmental stimuli and using this data to train the system in order to enhance desired performance metrics.

Unsteady fluid dynamics around a hovering flat-plate wing

The unsteady fluid dynamics around a hovering flat-plate wing with special attention to the effect of pitch on flow and forces has been investigated experimentally using particle image velocimetry and direct force measurements. The measurements are conducted on a wing that pitches symmetrically about the stroke reversal at a reduced frequency of k=0.32 and Reynolds number of Re=220. The Lagrangian finite time Lyapunov exponent method is used to analyze the unsteady flowfields by identifying dynamically relevant flow features such as the primary leading-edge vortex, secondary vortices, and topological saddles as well as their evolution within a flapping cycle. The flow evolution is divided into four stages that are characterized by the leading-edge vortex: 1) emergence, 2) growth, 3) liftoff, and 4) breakdown and decay. The saddle-point trajectory helps in identifying the leading-edge vortex liftoff, which occurs at the maximum stroke velocity. The flowfields are correlated with the aerodynamic forces, revealing that the maximum lift and drag are observed just before leading-edge vortex liftoff. The effect of a change in the pitch duration for a symmetric pitch is then discussed. The flow stages remain the same for the compared cases whereas the duration of flow stages varies. Furthermore, a phase lead and lag with respect to the stroke timing is introduced. Detailed flow development and force evolution is discussed to highlight the effect of varying the phase-shift on the aerodynamic characteristics of the hovering wing. Changing the pitching phase results in distinct flow changes that correlate with a higher lift production when the pitch precedes the stroke reversal and lower lift production when the pitch succeeds the stroke reversal.