Streamlines

Streamlines are a post-processing display type that represents velocity results by showing the path taken by a massless particle from a defined point. Each point along the streamline is tangent to the velocity vector of the fluid flow.

Typically, streamlines are used to present results of a flow analysis. Use streamlines to improve the interpretation and communication of velocity results.

Note:

• When viewing results on selected meshes or element groups, the entire streamline is always displayed, regardless of which meshes or element groups are displayed.

• Streamlines are available when you set the color display to contour plot.

Seed points and seed sets

To create a streamline display, you must define one or more seed points. Seed points are stored in seed sets. Seed sets are similar to the paths used for graphing results; you can reuse seed sets in multiple displays, and manage seed sets in the Post Processing Navigator.

Plotting contours on streamlines

A streamline display includes data from two results sets:

• A velocity result, which determines the path of the streamline, and, depending on the streamline style, may indicate components such as vorticity and divergence.

• A color display result, which determines the color contour displayed on the streamline.

The following figure shows two different results displayed as contours on the same ribbon streamline.

(1) Static pressure contours; (2) Fluid temperature contours.

You specify the velocity results to use when you create a seed set and generating streamlines. You select the contour results to display when editing your post view.

Streamline styles

There are four styles of streamline:

• Line—A simple streamline display. You can plot selected results values on streamlines as smooth contours.

• Ribbon—Displays each streamline as a constant-width ribbon, where the twist of the ribbon represents the vorticity of the flow.

• Tube—Displays each streamline as a tube, where the radius of the tube indicates the divergence of the flow.

• Bubbles—Displays spheres along the streamline, at a specified time increment. Bubbles are also used for animating steady-state streamlines.

Streamline generation

The default extraction parameters produce high-quality streamlines in the majority of cases. If necessary, you can adjust the parameter values in the Extraction Parameters group on the Seed Set dialog box to increase streamline accuracy, reduce resource usage, or generate streamlines that otherwise fail within the default parameters.

Velocity is defined as the change in position per the change in time (Δx / Δt). In a steady-state velocity field, once the instantaneous velocity at any position in the field is known, the next position along the velocity stream can be found by assigning a small value to Δt, multiplying it by the speed, and moving that distance along the velocity vector.

The distance between positions is the step size. On the Seed Set dialog box, you can decrease the value of the Maximum Step Size to increase the precision of the streamline. Be aware, however, that decreasing the maximum step size will increase use of system resources.

If you specify a very small step size, the software may encounter certain limits before the streamline completely traverses the velocity field. If this happens, you can increase the value for the Maximum Number of Steps or the Maximum Time Elapsed. The elapsed time is the sum of the Δt values assigned at each step.

The calculated elapsed time is used to define increments of constant Δt when setting up bubble streamlines or animating steady-state streamlines.

Where do I find it?

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partVelocity results loaded in a post viewContour plot color display
Command Finder	Edit Post View
Post Processing Navigator	Right-click a post view→Edit Post View
Dialog box	From the display type list, choose Streamlines

How do I

Create a seed set and generate streamlines

Set up a streamlines display

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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Streamlines, Simcenter 3D 2021.1 Series

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