Abstract
We develop a method for estimating the instantaneous lift coefficient on a rapidly pitching airfoil that uses a small number of pressure sensors and a measurement of the angle of attack. The approach assimilates four surface pressure measurements with a modified nonlinear state space model (Goman–Khrabrov model) through a Kalman filter. The error of lift coefficient estimates based only on a weighted-sum of the measured pressures are found to be noisy and biased, which leads to inaccurate estimates. The estimate is improved by including the predictive model in an conventional Kalman filter. The Goman–Khrabrov model is shown to be a linear parameter-varying system and can therefore be used in the Kalman filter without the need for linearization. Additional improvement is realized by modifying the algorithm to provide more accurate estimate of the lift coefficient. The improved Kalman filtering approach results in a bias-free lift coefficient estimate that is more precise than either the pressure-based estimate or the Goman–Khrabrov model on their own. The new method will enable performance enhancements in aerodynamic systems whose performance relies on lift.
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Acknowledgements
The support for this work by the US Air Force Office of Scientific Research FA9550-18-1-0440 with program manager Gregg Abate is gratefully acknowledged. Supported under the US Air Force Office of Scientific Research FA9550-14-1-0328 with program manager Douglas Smith is also gratefully acknowledged. The first author would like to thank the supported under ONR MURI Grant N00014-14-1-0533 with program manager Robert Brizzolara. The insightful suggestions from Professor C. Rowley and S. Otto at Princeton University are sincerely appreciated.
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An, X., Williams, D.R., Eldredge, J.D. et al. Lift coefficient estimation for a rapidly pitching airfoil. Exp Fluids 62, 11 (2021). https://doi.org/10.1007/s00348-020-03105-3
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DOI: https://doi.org/10.1007/s00348-020-03105-3