This work is focused on reduction of swirling in cases from hydraulic machinery and, thus, mitigation of instabilities associated with swirling flow. We study this problem analytically using the torque integral equation, numerically using computational fluid dynamics (CFD) simulations, and experimentally using a swirl generator that generates swirling flow approximating that in a draft tube of a hydro turbine operating at a part load, featuring an unsteady spiral vortex—the vortex rope. The analytical description elucidates the effect of different installations on the circumferential velocity. Unconventional conical perforated installations targeting at increasing the dissipation were proposed and tested. The rather unsatisfactory results led to proposing fins placed unconventionally away from the wall, closer to the diffuser axis, which were subsequently shown to be able to reliably suppress the unsteady vortex rope. Their effect is documented by an analysis of CFD results including the proper orthogonal decomposition as well as experimental observations and measurements.

Computer graphics visualization techniques for application on data from Computational Fluid Dynamics (CFD) simulations of the vortex rope, a phenomenon present in hydraulic turbines operating in off-design conditions, were devised. This included not only objects for visualization (what to visualize) but also methods of the visualization itself (how to do it). By means of advanced methods based particularly on volume rendering of Eulerian fields in combination with Lagrangian objects, various phenomena were captured, such as the motion of the vortex rope or the backflow zone. The data came from simulations using a scale-resolving hybrid turbulence model, the Stress-Blended Eddy Simulation. In such detailed simulations and other applications involving complex three-dimensional structures, proper visualization methods are needed to leverage the content captured in the resultant data.

This paper focuses on a fluid–structure interaction topic—the determination of added effects caused by fluid forces acting on a body, considering the standard linear equation of motion. We present various problems that assume small-displacement oscillations of single and multiple bodies in inviscid irrotational (potential) flow or viscous incompressible flow in both closed domain and external flow. For inviscid flow, effects of geometric parameters on the added effects were studied. The presented results extend results known from the literature. For viscous flow, frequency dependence of the added effects was studied for a wide range of frequency. The added effects were computed from data from numerical simulations of fluid flow, where the body oscillations were modeled using the dynamic mesh approach. Effects of the phase shift caused by the dynamic mesh were addressed. The added mass was compared with the corresponding value determined for inviscid flow where applicable. The results show strong dependence of the added effects on many parameters, making their proper computation challenging even for simplified cases.

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.