  The ability of vortices to induce aerodynamic loads on proximal surfaces
plays a significant role in a wide variety of flows. However, most studies of
vortex-induced effects primarily focus on analyzing the influence of the
rotation-dominated cores of vortices. In this work, we show that not only are
vortices in viscous flows surrounded by strain-dominated regions, but that
these regions are dynamically important and can sometimes even dictate the
induced aerodynamic loads. We demonstrate this for a pitching airfoil, which
exhibits dynamic stall and generates several force-inducing vortices. Using a
data-driven force partitioning method, we quantify the influence of vortices as
well as vortex-associated strain to show that our current understanding of
vortex-dominated phenomena, such as dynamic stall, is incomplete without
considering the substantial effect of strain-dominated regions that are
associated with vortices.
