Abstract
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.
Highlights
We propose a way of visualizing the whole 3D field of the finite-time Lyapunov exponent, a parameter connected with so-called Lagrangian coherent structures [29]
Suitable methods of computer graphics flow visualization for application on the vortex rope and possibly other phenomena were pursued in this paper
Common methods of vortex identification were tested to capture the vortex rope, as well as more elaborated ones: the M Z -criterion and the residual vorticity based on a triple decomposition of the velocity gradient tensor
Summary
Graphics Flow Visualization Methods in Vortex Rope Investigations. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Rajan and Cimbala [25] compared the static pressure and the mentioned vortex identification methods on a case with the vortex rope corresponding to the FLow INvestigation in a Francis Draft Tube (FLINDT) project [26]. They used a suitably selected isosurface and found out that visualizations based on the static pressure capture only the upper part of the vortex rope, while the vortex criteria capture the whole structure and its disintegration into smaller vortices downstream. Another aim of this paper is to devise computer graphics flow visualization methods suitable for studies of the vortex rope and possibly other similar phenomena. Energies 2021, 14, 623 are demonstrated on data from CFD simulations of flow downstream of a swirl generator that cover a wide range of operating points given by the swirl number
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
