A texture-based framework for spacetime-coherent visualization of time-dependent vector fields

We present a technique for direct visualization of unsteady flow on surfaces from computational fluid dynamics. The method generates dense representations of time-dependent vector fields with high spatio-temporal correlation using both Lagrangian-Eulerian advection and image based flow visualization as its foundation. While the 3D vector fields are associated with arbitrary triangular surface meshes, the generation and advection of texture properties is confined to image space. Frame rates of up to 20 frames per second are realized by exploiting graphics card hardware. We apply this algorithm to unsteady flow on boundary surfaces of, large, complex meshes from computational fluid dynamics composed of more than 250,000 polygons, dynamic meshes with time-dependent geometry and topology, as well as medical data.

We propose a new technique to visualize dense vector fields associated with unsteady fluid flows. This technique is based on a Lagrangian-Eulerian Advection (LEA) scheme, and it enables animations with high spatio-temporal correlation at interactive rates. We demonstrate the efficiency and efficacy of the technique in applications to numerical simulation of a shock interacting with a longitudinal vortex, and of ocean circulation in the Gulf of Mexico. The simplicity of the data structures and the facility of implementation suggest that LEA could become a useful component of any scientific visualization toolkit concerned with the display of unsteady flows.

In this paper, we propose a new technique to visualize dense representations of time-dependent vector fields based on a Lagrangian-Eulerian Advection (LEA) scheme. The algorithm produces animations with high spatio-temporal correlation at interactive rates. With this technique, every still frame depicts the instantaneous structure of the flow, whereas an animated sequence of frames reveals the motion a dense collection of particles would take when released into the flow. The simplicity of both the resulting data structures and the implementation suggest that LEA could become a useful component of any scientific visualization toolkit concerned with the display of unsteady flows.

The unsteady convective flow effects in a transonic compressor rotor with a circumferential-groove casing treatment are investigated in this paper. Experimental results show that the circumferential-groove casing treatment increases the compressor stall margin by almost 50% for the current transonic compressor rotor. Steady flow simulation of the current casing treatment, however, yields only a 15% gain in stall margin. The flow field at near-stall operation is highly unsteady due to several self-induced flow phenomena. These include shock oscillation, vortex shedding at the trailing edge, and interaction between the passage shock and the tip clearance vortex. The primary focus of the current investigation is to assess the effects of flow unsteadiness and unsteady flow convection on the circumferential-groove casing treatment. Unsteady Reynolds-averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) techniques were applied in addition to steady Reynolds-averaged Navier-Stokes (RANS) to simulate the flow field at near-stall operation and to determine changes in stall margin. The current investigation reveals that unsteady flow effects are as important as steady flow effects on the performance of the circumferential grooves casing treatment in extending the stall margin of the current transonic compressor rotor. The primary unsteady flow mechanism is unsteady flow injection from the grooves into the main flow near the casing. Flows moving into and out of the grooves are caused due to local pressure difference near the grooves. As the pressure field becomes transient due to self-induced flow oscillation, flow injection from the grooves also becomes unsteady. The unsteady flow simulation shows that this unsteady flow injection from the grooves is substantial and contributes significantly to extending the compressor stall margin. Unsteady flows into and out of the grooves have as large a role as steady flows in the circumferential grooves. While the circumferential-groove casing treatment seems to be a steady flow device, unsteady flow effects should be included to accurately assess its performance as the flow is transient at near-stall operation.

Investigation of the unsteady flow in a transonic axial compressor adopted in the compressed air energy storage system

The paper presents an efficient and accurate implementation of Unsteady Flow LIC (UFLIC) on the Graphics Processing Unit (GPU). We obtain the same, high quality texture representation of unsteady two-dimensional flows as the original, time-consuming method but leverage the features of today's commodity hardware to achieve interactive frame rates. Despite a remarkable number of recent contributions in the field of texture-based visualization of time-dependent vector fields, the present paper is the first to provide a faithful implementation of that prominent technique fully supported by the graphics pipeline.

The unsteady flow in stator–rotor interactions affects the structural integrity, aerodynamic performance of the stages, and blade-surface heat transfer. Numerous viscous and inviscid computer programs are used for the prediction of unsteady flows in two-dimensional and three-dimensional stator–rotor interactions. The relative effects of the various components of flow unsteadiness on heat transfer are under investigation. In this paper it is shown that for subsonic cases, the reduced frequency parameter for boundary-layer calculations is about two orders of magnitude smaller than the reduced frequency parameter for the core flow. This means that for typical stator–rotor interactions, the unsteady flow terms are needed to resolve the location of disturbances in the core flow, but in many cases the instantaneous disturbances can be input in steady-flow boundary-layer computations to evaluate boundary-layer effects in a quasi-steady approximation. This hypothesis is tested by comparing computations with experimental data on a turbine rotor for which there are extensive experimental heat transfer data available in the open literature. An unsteady compressible inviscid two-dimensional computer program is used to predict the propagation of the upstream stator disturbances into the downstream rotor passages. The viscous wake (velocity defect) and potential flow (pressure fluctuation) perturbations from the upstream stator are modeled at the computational rotor–inlet boundary. The effects of these interactions on the unsteady rotor flow result in computed instantaneous velocity and pressure fields. The period of the rotor unsteadiness is one stator pitch. The instantaneous velocity fields on the rotor surfaces are input in a steady-flow differential boundary-layer program, which is used to compute the instantaneous heat transfer rate on the rotor blades. The results of these quasi-steady heat-transfer computations are compared with the results of unsteady heat transfer experiments and with the results of previous unsteady heat transfer computations. The unsteady flow fields explain the unsteady amplitudes and phases of the increases and decreases in instantaneous heat transfer rate. It is concluded that the present method is accurate for quantitative predictions of unsteady heat transfer in subsonic turbine flows.

Abstract. The advent of low-cost pressure transducers capable of directly measuring water surface elevation enables continuous measurements of dynamic water surface slopes. This opens up a new possibility of dynamically monitoring unsteady flows (i.e., hysteresis) during the course of flood wave propagation. Hysteresis in this context refers to a looped stage–discharge rating caused by unsteadiness of flows. Hysteresis is monitored in this study using a continuous slope area (CSA) method, which uses Manning's equation to calculate unsteady discharges based on continuously measured water surface slopes. In the rising stage, water surface slopes become steeper than a steady water surface slope, resulting in higher discharges than steady-based discharges, while the trends are reversed in the falling stage. The CSA method applied to Clear Creek near Oxford (Iowa, USA) estimates the maximum differences of peak discharges by 30–40 %, while it shows sound agreements for a low to medium range of discharges against USGS steady-based records. The primary cause of these differences is the use of a single channel bed slope in deriving Manning's roughness coefficients. The use of a single channel bed slope (conceptually equal to the water surface slopes at every stage in uniform flow conditions) causes substantial errors in estimating the channel roughness, specifically at high stages, because non-uniformities of natural channels result in varying (non-uniform) steady water surface slopes at each stage. While the CSA method is promising for dynamically tracking unsteady water surface slopes and flows in natural streams, more studies are still needed to increase the accuracy of the CSA method in future research.

A new method for the synthesis of dense, vector-field aligned textures on curved surfaces is presented, called IBFVS. The method is based on image based flow visualization (IBFV). In IBFV two-dimensional animated textures are produced by defining each frame of a flow animation as a blend between a warped version of the previous image and a number of filtered white noise images. We produce flow aligned texture on arbitrary three-dimensional triangular meshes in the same spirit as the original method: texture is generated directly in image space. We show that IBFVS is efficient and effective. High performance (typically fifty frames or more per second) is achieved by exploiting graphics hardware. Also, IBFVS can easily be implemented and a variety of effects can be achieved. Applications are flow visualization and surface rendering. Specifically, we show how to visualize the wind field on the earth and how to render a dirty bronze bunny.

This paper is conceived as an extension in the analysis of the periodic stator-rotor interaction in a low-speed axial fan with inlet guide vanes. Here, the present work focuses on the deterministic fluctuations that occur in the axial gap between the blade rows. In particular, we present experimental data on the phase averaged velocity in the stator frame of reference. Detailed measurements of the flow field were obtained using hot-wire anemometry in a traverse sector that covered the whole span of the stage for a complete stator pitch. The blade-to-blade velocity gradient in the rotor passage is observed as an unsteady flow in the stator frame of reference due to the relative motion of the blades. As a consequence, this periodic fluctuation is superimposed on the steady vane-to-vane velocity distribution, resulting in a nonuniform unsteadiness with additional phase-dependent wake-blockage interaction. This phase-dependent interaction is determined by the difference between the overall deterministic fluctuation and the rotating spatial blade-to-blade distribution, when the latter is accurately transformed to the stator reference frame. The results revealed that high unsteadiness in the tip region is mainly derived from the radial increase of the blade-to-blade nonuniformities in the rotor, whereas the wake-blockage interaction exhibits a spanwise uniform distribution. Hence, the hub-to-tip torsion of the blades is responsible for setting off a major spatial distortion between the rows. Complementarily, we observed that a reduction in the rows’ spacing or an increase in the blade loadings leads to a higher wake-blockage interaction, modifying the impingement of the incoming stator wakes. In addition, the deterministic stresses were calculated by time averaging the phase-dependent velocity correlations and compared to the turbulent stresses. The deterministic stresses were also segregated in temporal, spatial, and spatial-temporal correlations in order to analyze the dominant mechanisms involved in their generation. At this point, the deterministic kinetic energy levels were found to be generally lower than turbulent kinetic energy levels, with both temporal and spatial correlations being the most significant terms of the tensor.

This paper describes an approach for interactive visualization of mixed scalar and vector fields, in which vector icons are generated from pre-voxelized icon templates and volume-rendered together with the volumetric scalar data. This approach displays simultaneously the global structure of the scalar field and the detailed features of the vector field. Interactive visualization is achieved with incremental image update, by re-rendering only a small portion of the image wherever and whenever a change occurs. This technique supports a set of interactive visualization tools, including change of vector field visualization parameters, real-time animation of vector icons advected within the scalar field, a zooming lens, and a local probe. Subject Terms: data visualisation; interactive systems; graphical user interfaces; rendering (computer graphics); interactive visualization; scalar fields; vector fields; vector icons; pre-voxelized icon templates; volume-rendered; volumetric scalar data; incremental image update; real-time animation; zooming lens; local probe

The analysis of data that consists of multiple vector fields can be greatly facilitated by the simultaneous visualization of the vector fields. An effective visualization must accurately reflect the key physical structures of the fields in a way that does not allow for an unintended bias toward one distribution. While there are several effective techniques to visualize a single vector field through equally spaced streamlines, applying these techniques to individual vector fields and combining them in a single image yields undesirable artifacts. In this paper, we present strategies for the effective visualization of two vector fields through the use of streamlines.

Streamline1 is one of the most widely used method in vector field visualization. However, with the expansion of data size, the existing methods cannot ensure the efficiency while maintaining high accuracy. In order to analyse the vector field efficiently, this paper proposes an algorithm for streamline visualization in unstructured vector field while keeping both efficiency and accuracy based on Kipfer's algorithm[1]. First, all grids are classified according to their Jordan canonical form. Then the streamline expressions in each grid cell are deduced for each kind of the grids, and we found that the expressions can be represented in a uniform way. Finally, the exit point of the streamline in the grid cell is calculated by solving the equation composed of the streamline expression and the equation of each face of the tetrahedron. The exit point can be obtained quickly and accurately by using Newton iterative method. The experimental results show that our algorithm is more efficient for streamline visualization with the same accuracy than Kipfer's algorithm.

In this paper, we present a high-quality texture-based enhanced approach for the visualization of unsteady vector fields. It adopts a scheme of streamline enhancement by applying a ID high-pass filter to flow textures along the orthogonal flow direction to enhance the intensity contrast among streamlines and improve the image quality of flow textures. A scheme of boundary supplement is also used to modulate the characteristic of particles flow. Using the color mapping of some scalar properties, such as magnitude, orientation and curvature, it is capable of displaying many properties of vector field which are helpful to analyze the features and topological flow patterns. It is capable of achieving a real-time rendering performance on a personal computer by using current graphics hardware.

Abstract. Pedestrian traffic flow estimation is essential for public place design and construction planning. Traditional data collection by human investigation is tedious, inefficient and expensive. Panoramic laser scanners, e.g. Velodyne HDL-64E, which scan surroundings repetitively at a high frequency, have been increasingly used for 3D object tracking. In this paper, a simultaneous detection and tracking (SDAT) method is proposed for precise and automatic pedestrian trajectory recovery. First, the dynamic environment is detected using two different methods, Nearest-point and Max-distance. Then, all the points on moving objects are transferred into a space-time (x, y, t) coordinate system. The pedestrian detection and tracking amounts to assign the points belonging to pedestrians into continuous trajectories in space-time. We formulate the point assignment task as an energy function which incorporates the point evidence, trajectory number, pedestrian shape and motion. A low energy trajectory will well explain the point observations, and have plausible trajectory trend and length. The method inherently filters out points from other moving objects and false detections. The energy function is solved by a two-step optimization process: tracklet detection in a short temporal window; and global tracklet association through the whole time span. Results demonstrate that the proposed method can automatically recover the pedestrians trajectories with accurate positions and low false detections and mismatches.