Bio: Dr. Chandan Bose has recently joined as an Assistant Professor of Aerospace Engineering at the School of Metallurgy and Materials, University of Birmingham. His research group will be focussed on investigating a variety of complex multiphysics problems involving coupled nonlinear interactions, among which unsteady aerodynamics, nonlinear aeroelasticity, and bio-inspired fluid-structure interaction problems will be of primary interest. Before joining the University of Birmingham, Dr. Bose played a pivotal role as a senior postdoctoral research associate contributing to an ERC project “Dandidrone” at the Vortex Interaction Laboratory, University of Edinburgh. His work revolved around deciphering the intricate fluid-structure interaction dynamics inherent in dandelion seed propulsion, culminating in its application to the development of microdrones. Additionally, he also served as an adjunct lecturer at the School of Engineering, University of Edinburgh. Earlier in his career, Dr. Bose embarked on a postdoctoral endeavor at the University of Liege, Belgium, during which he was bestowed with the Wallonie Bruxelles International Excellence Postdoctoral Fellowship and FNRS Postdoctoral Fellowship. This tenure was dedicated to unraveling the complexities of nonlinear aeroeelasticity. His academic journey commenced at the Department of Applied Mechanics, Indian Institute of Technology Madras, India, where he earned both his master’s and Ph.D. degrees in 2019. His Ph.D. research was on the dynamical analysis of the unsteady flow phenomena around a flapping wing through high-fidelity numerical simulations and wind tunnel experiments. Noteworthy accolades, including the Institute Research Award and V. Ramamurthy Best Thesis Award (both from IIT Madras), as well as the esteemed Indian National Academy of Engineering Innovative Project Award, underscored the significance of his contributions to doctoral research. His educational voyage commenced with a graduation in Civil Engineering from Jadavpur University, India, where he clinched the university gold medalist title, standing at the pinnacle of his batch.

Abstract: The present talk will focus on the wake dynamics and fluid-structure interactions involved in different flight mechanisms of small flyers in the low Reynolds number regime. The outline of the talk will be divided into two primary focus areas: flow dynamics of active and passive flight of small flyers. There are a variety of natural small flyers from the animal kingdom, like insects, who exploit their complex aerial acrobatics through active wing kinematics to generate sufficient aerodynamic forces to fly. On the other hand, there is another class of passive flyers from the plant kingdom, like dandelion seeds, which exhibit long-distance dispersal through a passive flight by extracting energy from the wind gusts and the updrafts. In the first case, the active flyers periodically use their flapping wings and exploit the wing flexibility to augment the aerodynamic efficiency. Although periodic flapping motions are usually expected to lead to periodic and organized wakes at low Reynolds numbers, our investigations have revealed a range of kinematic parameters, which gives rise to chaotic flow fields and in turn, unpredictable chaotic aerodynamic loads. We have established the route to chaotic transition in the flow past a flapping wing and unraveled the fundamental vortex interaction mechanisms responsible for manifesting chaos in the flow field. We have observed that even a small erratic behavior of the leading edge vortex could spell a complete eventual breakdown of a regular wake in the high Strouhal number regime. The presence of chaos is highly undesirable from the viewpoint of flapping flight control and presents a fundamental practical problem. To that end, we have discovered that the chordwise flexibility of the wings plays a pivotal role in regularizing the wake and inhibiting chaos. In the latter example of passive flyers, dandelion seeds exploit the wind gusts and updrafts in turbulent flows using a bundle of drag-enhancing bristles, called pappus. The highly porous filamentous pappus of the dandelion seed is simplistically modeled as a passively flying porous disc with a displaced center of mass to capture the essential dynamics from a macroscopic approach. Our study uncovers the role of porosity and permeability on the long dispersal of these biological seeds, such as dandelions, understanding the flight mechanisms deployed by nature to keep the dandelion seeds aloft. Furthermore, we systematically characterize the role played by the wind gusts and updrafts in enabling the long-distance wind dispersal of the dandelion seeds. The gust effect depends on the terminal velocity of the seed, which in turn is a function of Reynolds number, Darcy number, and the non-dimensional moment of inertia of the system. The fundamental wake-structure interactions in the vortex-dominated flow around the falling porous body provide us insight into the flight mechanism. An appropriate understanding of the flight mechanism of these small flyers and their gust response will directly benefit the design strategies of insect-scale drones and micro aerial vehicles. These futuristic devices are envisaged to have multi-fold applications in environmental monitoring in areas inaccessible to humans and in building distributed sensor network systems.