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Prediction of leading-edge-vortex initiation using criticality of the boundary layer

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Abstract

The initiation of leading-edge-vortex formation in unsteady airfoil flows is governed by flow criticality at the leading edge. While earlier works demonstrated the promise of criticality of leading-edge suction in governing LEV shedding, this criterion is airfoil and Reynolds number dependent. In this work, by examining results from Navier–Stokes computations for a large set of pitching airfoil cases at laminar flow conditions, we show that the onset of flow reversal at the leading edge always corresponds to the boundary-layer shape factor reaching the same critical value that governs laminar flow separation in steady airfoil flows. Further, we show that low-order prediction of this boundary-layer criticality is possible with an integral-boundary-layer calculation performed using potential-flow velocity distributions from an unsteady panel method. The low-order predictions agree well with the high-order computational results with a single empirical offset that is shown to work for multiple airfoils. This work shows that boundary-layer criticality governs LEV initiation, and that a low-order prediction approach is capable of predicting this boundary-layer criticality and LEV initiation.

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The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors would like to gratefully acknowledge Professor Jack Edwards of North Carolina State University (NCSU) for providing the REACTMB-INS code used for numerical results in this work. We also acknowledge the computing resources provided by North Carolina State University High Performance Computing Services Core Facility (RRID:SCR_022168).

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  1. Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, 27695, USA

    Hariharan Ramanathan & Ashok Gopalarathnam

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Ramanathan, H., Gopalarathnam, A. Prediction of leading-edge-vortex initiation using criticality of the boundary layer. Theor. Comput. Fluid Dyn. 37, 397–420 (2023). https://doi.org/10.1007/s00162-023-00648-z

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