@article{babu_narsipur_gopalarathnam_2024, title={Lift tailoring on unsteady airfoils with leading-edge vortex shedding using an inverse aerodynamic approach}, volume={36}, ISSN={["1089-7666"]}, DOI={10.1063/5.0208567}, abstractNote={In this paper, we present a physics-informed approach to tailor the lift profile of an unsteady airfoil through the execution of an appropriate maneuver. In previous research, a low-order aerodynamic model based on the unsteady thin airfoil theory was developed for predicting the flowfield and loads on airfoils undergoing arbitrary motions. The theory was phenomenologically augmented using the concept of leading edge suction parameter (LESP) to incorporate the capability to predict intermittent leading edge vortex (LEV) shedding. The criticality of LESP was used to predict the onset and termination of LEV shedding and thus model the effect of LEVs on the flowfield and loads for a prescribed motion. In the current work, an inverse aerodynamic formulation is developed based on this framework for tackling the inverse problem: to obtain the motion kinematics required for generating a prescribed lift profile for an airfoil operating in the dynamic-stall regime. The LEV-modeling capability of the aerodynamic model enables the motion-design algorithm to take into account the effect of complex phenomena, such as dynamic stall and LEV shedding, which are not taken into account in previous research approaches. Several case studies are presented to demonstrate various scenarios such as lift tracking using pitching and heaving motions, lift cancellation during unsteady motion, and the generation of a given lift profile using two equivalent motions. The kinematic profiles generated by the inverse formulation are also simulated using a high-fidelity unsteady computational fluid dynamics solver to validate the predictions.}, number={5}, journal={PHYSICS OF FLUIDS}, author={Babu, Arun Vishnu Suresh and Narsipur, Shreyas and Gopalarathnam, Ashok}, year={2024}, month={May} }
 @article{narsipur_ramesh_gopalarathnam_edwards_2023, title={Discrete vortex modeling of perching and hovering maneuvers}, ISSN={["1432-2250"]}, DOI={10.1007/s00162-023-00653-2}, journal={THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS}, author={Narsipur, Shreyas and Ramesh, Kiran and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2023}, month={May} }
 @article{narsipur_gopalarathnam_2023, title={Leading-Edge Suction Behavior of Unsteady Airfoils in Forward and Reverse Flows}, volume={68}, ISSN={["2161-6027"]}, DOI={10.4050/JAHS.68.022009}, abstractNote={To model unsteady airfoil aerodynamics in forward and reverse flows in a simple and robust manner requires a strong understanding of the complex flow dynamics and their relation to first-order concepts. The current work explores the relation between the leading-edge suction force, represented
 nondimensionally by the leading-edge suction parameter (LESP), and the flow physics of forward and reverse dynamic stall as a function of freestream Reynolds number, airfoil thickness, and motion kinematics for the NACA 0012, 0015, and 0018 airfoils using computational tools. The relation
 between the LESP and critical events associated with leading-edge vortex (LEV) shedding was found to be independent of flow direction barring the signature to identify LEV initiation. Leading-edge suction was observed to continue to increase after LEV initiation in reverse flow and could be
 attributed to the combined effect of a weak LEV and strong trailing-edge vortice. While LESP, forces, and moments were found to be moderately dependent on airfoil thickness and strongly dependent on the Reynolds number in forward flow conditions and the critical LESP, in addition, was weakly
 dependent on motion kinematics, the aerodynamics were observed to be largely independent of said parameters in reverse flow. This allows for a single critical LESP value to be used for symmetric airfoils to indicate LEV initiation when the blunt edge is experiencing reversed flow, a finding
 which serves to largely reduce the empirical dependencies while modeling unsteady reverse dynamic stall in low-order methods.}, number={2}, journal={JOURNAL OF THE AMERICAN HELICOPTER SOCIETY}, author={Narsipur, Shreyas and Gopalarathnam, Ashok}, year={2023}, month={Apr} }
 @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{narsipur_gopalarathnam_edwards_2022, title={Low-Order Modeling of Dynamic Stall on Airfoils in Incompressible Flow}, ISSN={["1533-385X"]}, DOI={10.2514/1.J061595}, abstractNote={ Airfoil dynamic stall in incompressible flow is characterized by two interacting viscous flow phenomena: time-varying trailing-edge separation and the shedding of intermittent leading-edge-vortex structures. In the current work, a physics based low-order method capable of modeling the interactions between the two flow phenomena is developed with the aim of predicting dynamic stall with only a few empirical tuning parameters. Large computational datasets are used to understand the flow physics of unsteady airfoils so as to augment an inviscid, unsteady airfoil theory to model the time-dependent viscous effects. The resulting model requires only three empirical coefficients for a given airfoil and Reynolds number, which could be obtained from a single moderate-pitch-rate unsteady motion for that airfoil/Reynolds number combination. Results from the low-order model are shown to compare excellently with computational and experimental solutions, in terms of both aerodynamic loads and flow-pattern predictions. In addition to formulating a method with limited empirical dependencies, the current research provides valuable insights into the flow physics of unsteady airfoils and their connection to rapidly predictable theoretical parameters. }, journal={AIAA JOURNAL}, author={Narsipur, Shreyas and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2022}, month={Sep} }
 @article{oruganti_narsipur_2021, title={Airfoil lift calculation using wind tunnel wall pressures}, ISSN={["2041-3025"]}, DOI={10.1177/09544100211038253}, abstractNote={ An experimental method to calculate lift using static pressure ports on the wind tunnel walls and its associated limits has been explored in this article. While the wall-pressure measurement (WPM) technique for lift calculation has been implemented by other researchers, there is a lack of literature on the sensitivity of the WPM method to airfoil chord length, model thickness, surface roughness, and freestream conditions. Chord sensitivity studies showed that the airfoil chord to test section length ratio plays an important role in the accuracy of the measurements. Models need to be appropriately sized for optimum performance of the WPM method. Additionally, choosing the correct scaling ratio also ensures independence of lift measurements from freestream Reynolds number conditions. Finally, a combination of symmetric and cambered airfoils with thicknesses varying from 6 % − 21 % were tested and successfully validated against reference data for a freestream chord Reynolds number range of 100,000 to 550,000. The WPM method was found to be sensitive to varying surface flow conditions and airfoil thickness and has been shown to be a viable replacement to traditional lift measurement techniques using load balances or airfoils with surface pressure ports. }, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING}, author={Oruganti, Sreevishnu and Narsipur, Shreyas}, year={2021}, month={Aug} }
 @article{saini_narsipur_gopalarathnam_2021, title={Leading-edge flow sensing for detection of vortex shedding from airfoils in unsteady flows}, volume={33}, ISSN={["1089-7666"]}, DOI={10.1063/5.0060600}, abstractNote={Sensing of vortex shedding in unsteady airfoil flows can be beneficial in controlling and positively harnessing their effects for increased aerodynamic performance. The time variation of the leading-edge suction parameter (LESP), which is a non-dimensional measure of the leading-edge suction force, is shown to be useful in deducing the various events related to vortex shedding from unsteady airfoils. The recently developed leading-edge flow sensing (LEFS) technique, which uses a few pressures in the airfoil leading-edge region for deducing the aerodynamic state of an airfoil, is adapted to deduce the variation of LESP during an unsteady motion in incompressible flow. For this purpose, the flow over the airfoil is divided into an outer-region flow over the chord, modeled using thin airfoil theory, and an inner-region flow over the leading edge, modeled as a flow past a parabola. By matching these two flows, relations are derived for calculating the LESP from a few pressures at the leading edge. By studying the variations of the LEFS outputs and the calculated LESP for various unsteady motions, guidelines are presented for detecting events related to vortex shedding: initiation, pinch-off, and termination. Computational and experimental results for additional unsteady motions confirm the effectiveness of the LEFS as a sensing technique for events associated with vortex shedding on unsteady airfoils.}, number={8}, journal={PHYSICS OF FLUIDS}, author={Saini, Aditya and Narsipur, Shreyas and Gopalarathnam, Ashok}, year={2021}, month={Aug} }
 @article{narsipur_hosangadi_gopalarathnam_edwards_2020, title={Variation of leading-edge suction during stall for unsteady aerofoil motions}, volume={900}, ISSN={["1469-7645"]}, DOI={10.1017/jfm.2020.467}, abstractNote={Abstract}, journal={JOURNAL OF FLUID MECHANICS}, author={Narsipur, Shreyas and Hosangadi, Pranav and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2020}, month={Oct} }
 @article{narsipur_gopalarathnam_edwards_2019, title={Low-Order Model for Prediction of Trailing-Edge Separation in Unsteady Flow}, volume={57}, ISSN={["1533-385X"]}, DOI={10.2514/1.J057132}, abstractNote={Computational and experimental results for pitching and plunging airfoils were used to study the time lag associated with boundary-layer convection and to develop a model that can be used to augmen...}, number={1}, journal={AIAA JOURNAL}, author={Narsipur, Shreyas and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2019}, month={Jan}, pages={191–207} }
 @inproceedings{howell_nag_mcknight_narsipur_adelegan_2015, title={A low-power wearable substance monitoring device}, DOI={10.1109/vcacs.2015.7439567}, abstractNote={Alcohol and illicit drug abuse has become a major problem in recent years. According to US Census, there are approximately 40 million teenagers between the age of 10-19, and 20% of them have used an illegal substance at least once in their lifetime. Therefore, by extrapolation, there are potentially 8 million drug abuse cases across the board. This opens up a major requirement for drug monitoring and devices capable of monitoring drug abusers or helping addicts recover. Previous research has shown that certain quantifiable physiological parameters become altered following illicit drug or alcohol consumption. A solution that addresses the problem of detecting drug abuse is the core focus of this research. Initial steps have been focused on developing a device in the form of a wrist-watch that is capable of measuring selected physiological parameters using commercially available sensors. An Android application with algorithms capable of determining if the user is under the influence of alcohol or drugs has been developed and tested.}, booktitle={2015 Virtual Conference on Application of Commercial Sensors}, author={Howell, J. and Nag, A. and McKnight, M. and Narsipur, S. and Adelegan, O.}, year={2015} }