The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform

Gary D Doolen - One of the best experts on this subject based on the ideXlab platform.

  • lattice boltzmann method on a curvilinear coordinate system vortex shedding behind a circular cylinder
    Physical Review E, 1997
    Co-Authors: Gary D Doolen
    Abstract:

    The interpolation-supplemented lattice Boltzmann equation (ISLBE) method is used to simulate the two-dimensional vortex shedding behind a circular cylinder at low Reynolds numbers. Simulations are carried out on a polar-coordinate grid system with a dense grid distributed near the cylinder surface. The Strouhal number, the drag, and the lift coefficients obtained from the simulations agree well with previous experimental measurements and classical computational fluid dynamics simulations. Comparisons of detailed flow patterns with other studies via streamlines and Streaklines are also satisfactory. The ability of the ISLBE scheme to simulate complicated long-term periodic flow phenomena is demonstrated.

  • lattice boltzmann method on a curvilinear coordinate system vortex shedding behind a circular cylinder
    Physical Review E, 1997
    Co-Authors: Gary D Doolen
    Abstract:

    The interpolation-supplemented lattice Boltzmann equation (ISLBE) method is used to simulate the two-dimensional vortex shedding behind a circular cylinder at low Reynolds numbers. Simulations are carried out on a polar-coordinate grid system with a dense grid distributed near the cylinder surface. The Strouhal number, the drag, and the lift coefficients obtained from the simulations agree well with previous experimental measurements and classical computational fluid dynamics simulations. Comparisons of detailed flow patterns with other studies via streamlines and Streaklines are also satisfactory. The ability of the ISLBE scheme to simulate complicated long-term periodic flow phenomena is demonstrated. {copyright} {ital 1997} {ital The American Physical Society}

Han-wei Shen - One of the best experts on this subject based on the ideXlab platform.

  • image based streamline generation and rendering
    IEEE Transactions on Visualization and Computer Graphics, 2007
    Co-Authors: Han-wei Shen
    Abstract:

    Seeding streamlines in 3D flow fields without considering their projections in screen space can produce visually cluttered rendering results. Streamlines will overlap or intersect with each other in the output image, which makes it difficult for the user to perceive the underlying flow structure. This paper presents a method to control the seeding and generation of streamlines in image space to avoid visual cluttering and allow a more flexible exploration of flow fields. In our algorithm, 2D images with depth maps generated by a variety of visualization techniques can be used as input from which seeds are placed and streamlines are generated. The density and rendering styles of streamlines can be flexibly controlled based on various criteria to improve visual clarity. With our image space approach, it is straightforward to implement the level of detail rendering, depth peeling, and stylized rendering of streamlines to allow for more effective visualization of 3D flow fields.

  • Numerical surface flow visualization
    1998
    Co-Authors: David L. Kao, Han-wei Shen
    Abstract:

    Surface oil flow is an experimental flow visualization technique that depicts the surface flow pattern near the body of the model. Traditionally, a particle tracking technique that generates streamlines near the model body is used to depict surface flows in CFD flow simulations. In this paper, we compared surface flows represented by streamlines with those represented by a texture technique known as Line Integral Convolution (LIC). We found that streamlines used to depict surface flows are discontinuous in general and the quality of the surface flow pattern is highly dependent on the placement of the streamlines. Whereas, the LIC technique clearly depicts surface flows that closely resemble surface oil flows. We also found that surface flows near regions of vortex structures and saddle points are not best shown using the streamline technique compared to the LIC technique. For unsteady flow simulations, we compared Streaklines with a new texture synthesis technique called Unsteady Flow Line Integral Convolution (UFLIC) that we have recently developed. UFLIC accurately reveals the dynamic behavior of unsteady surface flows during animation

David A. Lane - One of the best experts on this subject based on the ideXlab platform.

  • Visualizing time-varying phenomena in numerical simulations of unsteady flows
    1996
    Co-Authors: David A. Lane
    Abstract:

    Also appeared as paper AIAA-96-0048 in the 34th Aerospace Sciences Meeting & Exhibit. Streamlines, contour lines, vector plots, and volume slices (cutting planes) are commonly used for flow visualization. These techniques are sometimes referred to as instantaneous flow visualization techniques because calculations are based on an instant of the flow field in time. Although instantaneous flow visualization techniques are effective for depicting phenomena in steady flows, they sometimes do not adequately depict time-varying phenomena in unsteady flows. Streaklines and timelines are effective visualization techniques for depicting vortex shedding, vortex breakdown, and shock waves in unsteady flows. These techniques are examples of time-dependent flow visualization techniques, which are based on many instants of the flow fields in time. This paper describes the algorithms for computing Streaklines and timelines. Using numerically simulated unsteady flows, Streaklines and timelines are compared with streamlines, contour lines, and vector plots. It is shown that Streaklines and timelines reveal vortex shedding and vortex breakdown more clearly than instantaneous flow visualization techniques

  • Visualization of Numerical Unsteady Fluid Flows
    1995
    Co-Authors: David A. Lane
    Abstract:

    Instantaneous streamlines are commonly used to visualize particle paths in steady flows. It is shown, however, that Streaklines are often more appropriate for unsteady flows. The typical size of unsteady flow simulations makes interactive visualization difficult if not impossible. Two common approaches for visualizing unsteady flows are described. The advantages and disadvantages of each are discussed. Many visualization systems have been developed for steady flows, yet relatively few have been developed specifically for those that are unsteady. The system developed at NASA Ames Research Center has produced effective visualization for many unsteady flows. The features of this system are introduced and some results are shown. Future directions are also discussed

Moshe Rosenfeld - One of the best experts on this subject based on the ideXlab platform.

  • Calculation of Streaklines for time periodic flows
    AIAA Journal, 1996
    Co-Authors: Moshe Rosenfeld
    Abstract:

    The calculation of Streaklines for complex time-dependent flows is confronted with severe difficulties due to the huge data sets involved. In the present work we propose a storage reduction method for tune-periodic flows. The method is based on the observation that many time-periodic flows can be accurately approximated using a small number of Fourier terms. By storing only the significant harmonics of the Fourier decomposition, the storage (disk space and core memory) required for calculating Streaklines can be reduced by one order of magnitude or more. The reduced storage permits the calculation of the Streaklines after completing the solution of the equations, rather than calculating a set of predefined Streaklines simultaneously with the solution of the flow. This significantly enhances the capability of studying interactively complex flowfields. Test cases confirm the assumption that a small number of Fourier terms is adequate for calculating accurately the Streaklines of complex flows. HE simulation of time-dependent flows is one of the major top- ics of interest in contemporary computational fluid dynamics (CFD) studies. With the increase in computing power availability, complex unsteady flows can be calculated, creating huge data sets. In typical three-dimensional cases,

  • calculation of Streaklines for time periodic flows
    AIAA Journal, 1996
    Co-Authors: Moshe Rosenfeld
    Abstract:

    The calculation of Streaklines for complex time-dependent flows is confronted with severe difficulties due to the huge data sets involved. In the present work we propose a storage reduction method for tune-periodic flows. The method is based on the observation that many time-periodic flows can be accurately approximated using a small number of Fourier terms. By storing only the significant harmonics of the Fourier decomposition, the storage (disk space and core memory) required for calculating Streaklines can be reduced by one order of magnitude or more. The reduced storage permits the calculation of the Streaklines after completing the solution of the equations, rather than calculating a set of predefined Streaklines simultaneously with the solution of the flow. This significantly enhances the capability of studying interactively complex flowfields. Test cases confirm the assumption that a small number of Fourier terms is adequate for calculating accurately the Streaklines of complex flows. HE simulation of time-dependent flows is one of the major top- ics of interest in contemporary computational fluid dynamics (CFD) studies. With the increase in computing power availability, complex unsteady flows can be calculated, creating huge data sets. In typical three-dimensional cases, <9(106) mesh points and (9(104) time steps are required, generating data sets of (9(1010) words of storage. In two-dimensional cases less storage is required (<9(108) words), but still it might be excessive even when large supercom- puters are used, not to mention workstations that are mostly used for postprocessing the results. These large data sets confront difficult challenges in the postpro- cessing of flow simulations. One of the common flow visualization techniques is based on the calculation of the Streaklines that mimic dye-injection experiments. This calculation is computationally in- tensive. Yet, the main obstacle in the case of time-dependent flows is the need to store (both on disk and in memory) large data sets (the whole evolution of the flow). One way to overcome this problem is to calculate the Streaklines simultaneously with the solution of the flow equations. This necessarily means that the release points and release rate of the particles should be predetermined. The flow cannot be studied interactively, which is a severe shortcoming in the case of complex flowfields. Time-periodic flows are a special class of time-dependent flows. Time-periodic flows are obtained as self-excited flows (e.g., the von Karman vortex street) or by forced oscillating perturbations (e.g., the flow in blood vessels or certain hydraulic devices). Sim- ple time-periodic flows (with a narrow spectra) are mostly found in low or intermediate Reynolds (Re) number cases, but certain high Reynolds number flows can be also approximated as periodic flows. In the present article, we suggest how to overcome some of the problems associated with the calculation of Streaklines in time- periodic flows by using the Fourier transform of the solution. The so- lution itself is obtained from any unsteady flow solver. This approach might be appealing if a small number of harmonics can accurately approximate the time-dependent solution. We will demonstrate that in certain cases the saving in storage space and core memory might be more than one order of magnitude. This saving can be utilized for calculating Streaklines interactively even for solutions employ- ing a very large number of mesh points, a task that is in many cases impossible otherwise.

Mark Christopher Thompson - One of the best experts on this subject based on the ideXlab platform.

  • Spiral Streaklines in pre-vortex breakdown regions of axisymmetric swirling flows
    Physics of Fluids, 1995
    Co-Authors: Kerry Hourigan, Lachlan Graham, Mark Christopher Thompson
    Abstract:

    In steady swirling flows in closed cylinders, it has been common to observe the transition to spirals of otherwise straight dye Streaklines. This occurs in the regions where bubble type breakdown occurs but at a slightly lower Reynolds number. These regions are of particular interest for those seeking to explain the origins of vortex breakdown. The hitherto unexplained occurrence of the spiral Streaklines, postulated previously to be due to non‐axisymmetry of the flow, is found to be due to small offsets of the dye injection from the central axis. The important implications of this finding are that (i) non‐axisymmetry is not a necessary route to bubble‐type vortex breakdown, and (ii) that flows displaying spiral Streaklines may be still sufficiently axisymmetrical for comparison with numerical and theoretical treatments of the breakdown phenomenon.