Marek Pátý

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.

Vortices belong to the most important phenomena in fluid dynamics and play an essential role in many engineering applications. They can act detrimentally by harnessing the flow energy and reducing the efficiency of an aerodynamic device, whereas in other cases, their presence can be exploited to achieve targeted flow conditions. The control of the vortex parameters is desirable in both cases. In this paper, we introduce an optimization strategy for the control of vortices in the wake of a bluff body. Flow modelling is based on RANS and DES computations, validated by experimental data. The algorithm for vortex identification and characterization is based on the triple decomposition of motion. It produces a quantitative measure of vortex strength which is used to define the objective function in the optimization procedure. It is shown how the shape of an aerodynamic device can be altered to achieve the desired characteristics of vortices in its wake. The studied case is closely related to flame holders for combustion applications, but the conceptual approach has a general applicability to vortex control.