Low-Order Modeling of Incompressible, Unsteady Airfoil Aerodynamics

Unsteady airfoils 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 this research, a physics based low-order method capable of modeling the interactions between two flow phenomena was developed with the aim of predicting dynamic stall with only a few empirical tuning parameters. Large computational data sets 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 compare excellently with computational and experimental solutions, both in terms of aerodynamic loads and flow-pattern predictions, over a very large range of unsteady motions spanning a diverse range of applications from insect flight to aeronautical flight. 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.

Publications:

  • Sudharsan, S., Narsipur, S. and Sharma, A. (2022) "Evaluating Dynamic Stall Onset Criteria for Mixed and Trailing-Edge Stall," AIAA Journal (in review).
  • Narsipur, S. and Gopalarathnam, A. (2022) "Leading-Edge Suction Behavior of Unsteady Airfoils in Forward and Reverse Flows," Journal of the American Helicopter Society (accepted).
  • Narsipur, S., Gopalarathnam, A., and Edwards, J. R. (2022) "Low-Order Modeling of Dynamic Stall on Airfoils in Incompressible Flow," AIAA Journal (accepted).
  • Narsipur, S. (2022) "Effect of Reynolds Number and Airfoil Thickness on the Leading-Edge Suction Force in Unsteady Flows," Theoretical and Computational Fluid Dynamics. | doi: 10.1017/jfm.2020.467
  • Narsipur, S., Hosangadi, P., Gopalarathnam, A., and Edwards, J. R. (2020) "Variation of Leading-Edge Suction During Stall for Unsteady Aerofoil Motions," Journal of Fluid Mechanics, Vol. 900, Issue A25. | doi: 10.1007/s00162-022-00621-2
  • Narsipur, S., Gopalarathnam, A., and Edwards, J. R. (2019) "Low-Order Model for Prediction of Trailing-Edge Separation in Unsteady Flow," AIAA Journal, Vol. 57, Issue 1, pp. 191-207. | doi: 10.2514/1.J057132
  • Sudharsan, S., Narsipur, S., and Sharma, A. (2022) "Evaluating Dynamic Stall Onset Criteria for Mixed and Trailing-Edge Stall," Proc. of the 2022 AIAA Virtual SciTech 2022 Forum, AIAA Paper 2022-1983. | doi: 10.2514/6.2022-1983
  • Ramanathan, H., Narsipur, S., and Gopalarathnam, A. (2019) "Airfoil Lift Calculation Using Wind Tunnel Wall Pressures," Proc. of the 2019 AIAA Aviation Forum, AIAA Paper 2019-3590, Dallas, TX. | doi: 10.2514/6.2019-3590
  • Narsipur, S., Gopalarathnam, A., and Edwards, J. R. (2018) "Low-Order Modeling of Airfoils with Massively Separated Flow and Leading-Edge Vortex Shedding," Proc. of the 2018 AIAA SciTech Forum, AIAA Paper 2018-0813, Kissimmee, FL. | doi: 10.2514/6.2018-0813
  • Narsipur, S., Hosangadi, P., Gopalarathnam, A., and Edwards, J. R. (2016) "Variation of Leading-Edge Suction at Stall for Steady and Unsteady Airfoil Motions," Proc. of the 2016 AIAA SciTech Forum, AIAA Paper 2016-1354, San Diego, CA. | doi: 10.2514/6.2016-1354
  • Narsipur, S., Gopalarathnam, A., and Edwards, J. R. (2014) "A Time-Lag Approach for Prediction of Trailing-Edge Separation in Unsteady Flow," Proc. of the 2014 AIAA Aviation Forum, AIAA Paper 2014-2701, Atlanta, GA. | doi: 10.2514/6.2014-2701

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