A vorticity-based criterion to characterise leading edge dynamic stall onset

We propose a more conservative, physically-intuitive criterion, namely, the boundary enstrophy flux ( $BEF$ ), to characterise leading-edge-type dynamic stall onset in incompressible flows. Our results are based on wall-resolved large-eddy simulations of pitching aerofoils, with fine spatial and temporal resolution around onset. observe that $|BEF|$ reaches maximum within regime identified. By decomposing contribution from flow field, we find dominant arises laminar leading edge region, due combined effect large clockwise vorticity favourable pressure gradient. A relatively small originates transitional/turbulent separation bubble (LSB) LSB-induced counter-clockwise adverse This being nearly independent integration length as long region very close is included. characteristic yields major advantage partial or complete inclusion noisy LSB can be filtered out, without changing peak location time significantly. Next, analytically relate net wall shear show its critical value $=\max (|BEF|)$ ) corresponds instant prevailing at wall. Finally, have also compared suction parameter $LESP$ (Ramesh et al. , J. Fluid Mech. vol. 751, 2014, pp. 500–538) former between $0.3^{\circ }$ $0.8^{\circ rotation earlier.