@article{suresh babu_narsipur_bryant_gopalarathnam_2022, title={Leading-edge-vortex tailoring on unsteady airfoils using an inverse aerodynamic approach}, volume={34}, ISSN={["1089-7666"]}, DOI={10.1063/5.0090328}, abstractNote={In this paper, we present an approach to obtain a desired leading-edge vortex (LEV) shedding pattern from unsteady airfoils through the execution of suitable motion kinematics. Previous research revealed that LEV shedding is associated with the leading-edge suction parameter (LESP) exceeding a maximum threshold. A low-order method called LESP-modulated discrete vortex method (LDVM) was also developed to predict the onset and termination of LEV shedding from an airfoil undergoing prescribed motion kinematics. In the current work, we present an inverse-aerodynamic formulation based on the LDVM to generate the appropriate motion kinematics to achieve a prescribed LESP variation, and thus, the desired LEV shedding characteristics from the airfoil. The algorithm identifies the kinematic state of the airfoil required to attain the target LESP value through an iterative procedure performed inside the LDVM simulation at each time step. Several case studies are presented to demonstrate design scenarios such as tailoring the duration and intensity of LEV shedding, inducing LEV shedding from the chosen surface of the airfoil, promoting or suppressing LEV shedding during an unsteady motion on demand, and achieving similar LEV shedding patterns using different maneuvers. The kinematic profiles generated by the low-order formulation are also simulated using a high-fidelity unsteady Reynolds-averaged Navier–Stokes method to confirm the accuracy of the low-order model.}, number={5}, journal={PHYSICS OF FLUIDS}, author={Suresh Babu, Arun Vishnu and Narsipur, Shreyas and Bryant, Matthew and Gopalarathnam, Ashok}, year={2022}, month={May} }
 @article{sureshbabu_medina_rockwood_bryant_gopalarathnam_2021, title={Theoretical and experimental investigation of an unsteady airfoil in the presence of external flow disturbances}, volume={921}, ISSN={["1469-7645"]}, DOI={10.1017/jfm.2021.484}, abstractNote={Abstract While studies on unsteady airfoils in a uniform free stream are abundant, the quest for efficient man-made propulsion and energy harvesting calls for an improved understanding and predictive capability of unsteady airfoils encountering external flow disturbances. In this paper, we conduct experimental and theoretical investigations of the interactions between an airfoil engaged in unsteady motion and external flow disturbances generated by an upstream source. The flow field interactions are experimentally studied using particle-image velocimetry and finite-time Lyapunov exponent techniques. An interesting outcome of the interactions is an interruption of leading-edge vortex (LEV) shedding from the airfoil and a consequent modulation of the lift history, which are dependent on the phase of the disturbances relative to the airfoil kinematics. A low-order model for an unsteady airfoil encountering the disturbances is built upon the leading-edge suction parameter (LESP)-modulated discrete-vortex method (LDVM) developed by Ramesh et al. (J. Fluid Mech., vol. 751, 2014, pp. 500–538). The LDVM distils the determination of the LEV shedding characteristics of unsteady airfoils to a single parameter, the LESP. We show that the LDVM, modified for the current work, is able to predict the effect of the disturbances on the LEV shedding characteristics of the airfoil and the associated lift history in good agreement with experimental observations. In addition to being a predictive tool, the LDVM also augments the experimental study by providing a theoretical framework and various graphical approaches to analyse the flow phenomena from a fundamental perspective and elucidate the role of different factors governing the flow field evolution.}, journal={JOURNAL OF FLUID MECHANICS}, author={SureshBabu, ArunVishnu and Medina, Albert and Rockwood, Matthew and Bryant, Matthew and Gopalarathnam, Ashok}, year={2021}, month={Jul} }