This paper demonstrates how the viscous acceleration vector field can be used in the study of vortical structures and, more generally, in flow topology analysis. First, the problem of frame dependence in vortex identification and flow topology analysis is revisited. The viscous acceleration vector field is then introduced as a suitable objective quantity, being independent of both frame translation and rotation. We propose several innovative approaches based on it. Following an idea from the literature of treating the viscous acceleration field as a pseudo-velocity field, we show that its integral curves (or streamlines) can be utilized for flow topology analysis. Thanks to the objectivity, they reveal structures that may be hidden in frame-dependent velocity representations. To support this framework, we employ a less widely recognized Eulerian definition of streamline curvature and torsion. Furthermore, we show that the Eulerian representation of the curvature of viscous acceleration field lines can be used in connection with a vortex identification method (in this case residual vorticity) to obtain enhanced visualizations of vortical structures through volume rendering. The proposed methods are tested on three distinct cases of computational fluid dynamics (CFD) simulations, ranging from laminar flow to fully resolved turbulent flow. The results support their applicability in the post-processing of CFD data.
Urban et al. (Fri,) studied this question.