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# Periodic Streamline Introduction

Introduction:

New in EnSight 10.2, is the ability to generate "Periodic Streamlines". This allows models which were solved using Periodic Boundaries (sometimes referred to as Cyclic Boundaries) to create streamlines which re-enter the domain when the streamline exits through one of the periodic face. The re-enter point is the corresponding location on the matching periodic face. This can be quite helpful in visualizing a complete streamline, rather than the streamline stopping when it has reached the physical extent of the domain (rather than the computational extent of the domain). This capability exists for both Streamlines (steady state) and Pathlines (transient).

Procedure:

There are two basic items which need to be setup for calculating Periodic Streamlines. (1) The parent of the streamline (typically the fluid part(s)) must have their periodicity setup within the "Visual Symmetry" dialog box. (2) When creating the streamline, you must have the "Compute Using Periodicity" option turned ON.

Step 1:

The Parent of the streamline (typically the fluid part(s)) must have their periodicity setup. For each parent part, the Visual Symmetry Dialog must be setup for the appropriate rotational periodicity.

The Axis of Periodicity must be set.

The Number of sections in a full 360 degrees must be set.

Step 2:

The creation of the streamline must have the "Compute using Periodicity" toggle enabled. This toggle can be found in the "Advanced" section of the Create Traces Dialog:

Notes:

1. Most solvers apply this periodicity as a face boundary condition. However, in EnSight, the specification of periodicity is done to the fluid domain, and NOT to the periodic face. In the example below, both the orange and blue parts need to be specified as periodic for streamlines to correctly pass through. If you fail to specify the blue part as periodic, the streamlines can appear to stop at the interface.

2. As the streamline exits the physical domain of the parents, the parents are checked for their "periodicity", and if on, EnSight then looks at the periodic copy for existence of a domain and continues to integrate the streamline. The visual presentation of the periodic streamline remains within the physical boundaries of the parent part.

3. Passages can have different periodic (angular) extents. Each different periodic (angular) extent should be a different part, so that you can specify the appropriate periodicity sector count for each angular extent. In the example below, there are at least 3 fluid parts, allowing 3 different angular repeat sectors. You can see that this single rake of streamlines can be correctly computed through the different angular passages, which in this case, results in what appears to be many streamlines in the downstream portion (due to high swirl).

4. To visualize the more than one passage of streamlines, you must do the following two steps: (1) Fluid Parent: Turn on the Rotational Symmetry and Instances in the Part Visual Symmetry Dialog, (2) Streamline Part: Toggle on the "Visible" in the Part Visual Symmetry Dialog.

For the Fluid Parents, the dialog would look like:

For the Streamline Part, the dialog would look like:

The reason why you only have a visible toggle in the Streamline's Part Visual Symmetry Dialog is that the streamline may pass through different angular extents, requiring differing amounts of rotational offset along it's path. Therefore, it does not make sense to have an single angular setting for the streamline. Instead, EnSight determines the angular setting based on which parent it currently is contained.

In the end, you can visualize a continuous streamline from inlet to outlet by visualizing more than a since instance:

For a generic example to try yourself, please find below a link to an EnSight session file containing an example dataset.

You have a single .ens file. Simply load this into EnSight. For setup, you will need to know that the periodicity angular sector count is 41 (there are 41 sections in 360 degrees) about the X-axis. You should be able to follow the above instructions to try out periodic streamlines.

Caveats:

As of 22-Jan, the following caveats exist:

A. Does not work with Massed Traces

B. Does not work with Surface Restricted Traces.

C. Only works in Rotationally Periodic models.