1. Streak Ball Animation
  2. Writing an MPEG file

The purpose of this section is to create an animation using streak balls to visualize the flow through the pipe/duct geometry, which has been studied in the previous section (Turbulent flow near a pipe/duct junction).


In the "Visualization Object Manager" panel, highlight the STREAK_LINE object and turn the Tubes toggles ON. Repeat this step for the STREAK_LINE_2 object.

Create a New... STREAK_LINE and turn the Balls toggle ON. Set the Radius to 0.01, the Spacing to 0.2 (The Radius setting controls the size of the balls and the Spacing controls the spacing between streak balls along a streak line).

Turn the Size by toggle ON, and select P (Pressure) as the scalar variable, and then set the Magnifer to 0.03 and modify the Radius value to 0.07.

Now the size of the balls will represent the pressure : since the magnifer is less than unity, high pressures will correspond to small radii.

The STREAK_LINE_2 object is build in the same way.


The Animation Manager panel is displayed after selecting the WIREFRAME object (Fig. 1).

Fig. 1 : Animation Manager Panel


The first KeyFrame of the animation is created using the current Viewer image.

The Number of Frames is set to 96. Therefore, a 4 seconds long animation (playing 24 frames per second) will be produced.

In the "Visualization Object Manager" panel, select the STREAK_LINE_3 and set the Offset Value to 6 : the streak balls will then move along the flow inside the pipe.

The STREAK_LINE_4 is created in the same way. In the "Animation Manager" panel, press New to create KeyFrame_1.

The Make MPEG toggle is clicked on and the Settings button is pressed.The "MPEG Settings" panel is activated (Fig.2).

Fig. 2 : "MPEG Settings" Panel


Write a name for the animation in the appropriate box and click OK. Press Rewind and then Play in the Animation Manager to create the MPEG file.


The figure 3 below shows the streak ball animation.

Fig. 3 : Streak Ball Animation in the Pipe/Duct Geometry

Click here to animate (MPEG file - 1320 Ko).


The speed at each ball location on a streak line is estimated by the colour of the balls. The pressure is estimated by the size of the balls, knowing that high pressures correspond to small radii. However, the pressure is low near the junction as it should be in reality. The balls in the duct are getting smaller as the X-coordinate increases, therefore the pressure decreases along the duct as expected by the theory.

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