Visualization of intricate flow structures for vortex breakdown analysis

Abstract

Figure 1: Vortex breakdown bubble in numerical simulation of a cylindrical container. Flow topology is illustrated with stagnation points (red), singularity paths (yellow), and streamlines (blue) on three axially oriented cutting planes. Volume rendering illustrates additional aspects of flow structure, using a two-dimensional transfer function (widget, right) of a Jacobian-related invariant (horizontal axis) and vorticity (vertical axis). ABSTRACTVortex breakdowns and flow recirculation are essential phenomena in aeronautics where they appear as a limiting factor in the design of modern aircrafts. Because of the inherent intricacy of these features, standard flow visualization techniques typically yield cluttered depictions. The paper addresses the challenges raised by the visual exploration and validation of two CFD simulations involving vortex breakdown. To permit accurate and insightful visualization we propose a new approach that unfolds the geometry of the breakdown region by letting a plane travel through the structure along a curve. We track the continuous evolution of the associated projected vector field using the theoretical framework of parametric topology. To improve the understanding of the spatial relationship between the resulting curves and lines we use direct volume rendering and multi-dimensional transfer functions for the display of flow-derived scalar quantities. This enriches the visualization and provides an intuitive context for the extracted topological information. Our results offer clear, synthetic depictions that permit new insight into the structural properties of vortex breakdowns.

Extraction and Visualization of Swirl and Tumble Motion from Engine Simulation Data

“…In this paper, we address these deficiencies by combining a topological analysis of the boundary flow with a hybrid approach that leverages 2D topology to explore the 3D structure of a vector field [17]. Fig.…”

“…It was shown previously [17] that a moving cutting plane (traversing the volume of the dataset) on which the vector field is resampled and projected at regular intervals can be a powerful tool in the analysis of 3D datasets. The projection of the vector field on the plane effectively manages to discard structures orthogonal to the plane, but preserves plane-parallel flow patterns.…”

“…In addition, the strength of the rotation (as given by the modulus of λ 2 ) is not visualized. Interactive volume rendering has also been applied in this context [15,17] and is able to overcome most of the difficulties related to isosurfaces. As described in [17], we have not attempted to apply volume rendering directly to the unstructured grid but have employed a resampling scheme that results in a rectilinear grid covering the region of interest (in our cases, the cylinder).…”

Feature‐based adaptive mesh refinement for wingtip vortices

“…Each of these methods has advantages and disadvantages that have been documented in the literature. Hybrid methods, which exploit multiple detection methods, have also been developed [37][38][39].…”

On the Role of Topology in Focus+Context Visualization

“…The dense and direct depiction of the flow is limited to just a small region of the data to avoid visual clutter. Further examples of topological visual representations of flow can be found in related works [6,8,13,14]. …”