Step 8: Pathlines

  Pathlines are the lines traveled by neutrally buoyant particles in equilibrium with the fluid motion. Pathlines are an excellent tool for visualization of complex three-dimensional flows. In this example, you will use pathlines to examine the flow around and in the wake of the module.

1.   Create a rake from which the pathlines will emanate.

Surface $\rightarrow$ Line/Rake...

(a)   Select Rake from the Type drop-down list.

  A rake surface consists of a specified number of points equally spaced between two specified endpoints. A line surface (the other option in the Type drop-down list) is a line that includes the specified endpoints and extends through the domain; data points on a line surface will not be equally spaced.

(b)   Retain the default value of 10 for Number of Points.

  This will generate 10 pathlines.

(c)   Enter a starting coordinate of ( 1.0, 0.105, 0.07) and an ending coordinate of ( 1.0, 0.25, 0.07) in the End Points group box.

  This will define a vertical line in front of the module, about halfway between the centerline and edge.

(d)   Enter pathline-rake for New Surface Name.

  You will refer to the rake by this name when you plot the pathlines.

(e)   Click Create and close the Line/Rake Surface dialog box.

2.   Draw the pathlines (Figure  24.15).

Graphics and Animations Pathlines Set Up...

(a)   Enable Draw Mesh in the Options group box to open the Mesh Display dialog box.

i.   Ensure that Faces is enabled in the Options group box.

ii.   Retain the selection of board-top and chip from the Surfaces selection list.

  These surfaces should already be selected from the earlier exercise where the mesh was displayed with velocity vectors, Step 6: Velocity Vectors.

iii.   Close the Mesh Display dialog box.

(b)   Enter 0.001 inch for Step Size.

(c)   Enter 6000 for Steps.

Note:   A simple rule of thumb to follow when you are setting these two parameters is that if you want the particles to advance through a domain of length $L$, the Step Size times the number of Steps should be approximately equal to $L$.

(d)   Set Path Coarsen to 5.

  Coarsening the pathline simplifies the plot and reduces the plotting time. The coarsening factor specified for Path Coarsen indicates the interval at which the points are plotted for a given pathline in any cell.

(e)   Select pathline-rake from the Release from Surfaces selection list.

(f)   Click Display.

  The pathlines will be drawn on the surface.

(g)   Rotate the display so that the flow field is in front and the wake of the chip is visible as shown in Figure  24.15.

Figure 24.15: Pathlines Display

3.   Write the pathlines to a file.

(a)   Enable Write to File in the Options group box.

(b)   Click the Write... button to open the Select File dialog box.

  The Display button will change to a Write... button when you enable the Write to File option.

i.   Enter chip-pathline for Fieldview File.

ii.   Click OK to close the Select File dialog box.

   ANSYS FLUENT will save the file in Fieldview format .fvp extension.

4.   Display pathlines as spheres.

Graphics and Animations Pathlines Set Up...

(a)   Disable Write to File in the Options group box.

(b)   Select sphere from the Style drop-down list.

(c)   Click the Attributes... button to open the Path Style Attributes dialog box.

i.   Enter 0.0005 for Diameter.

ii.   Click OK to close the Path Style Attributes dialog box.

(d)   Enter 1 inch for Step Size and 1000 for Steps respectively.

(e)   Set Path Skip to 2 and Path Coarsen to 1.

(f)   Retain the selection of pathline-rake in the Release from Surfaces selection list.

(g)   Click Display.

  The spherical pathlines will be drawn along the surface.

(h)   Rotate the display so that the flow field is in front and the wake of the chip is visible as shown in Figure  24.16.

Figure 24.16: Sphere Pathlines Display

(i)   Select Surface ID from the lower Color by drop-down list.

(j)   Click Display and close the Pathlines dialog box (Figure  24.17).

  This will color the pathlines by the surface they are released from.

Figure 24.17: Sphere Pathlines Colored by Surface ID

Note:   You can also create solution animations for pathlines using Animation Sequence dialog box.

Calculation Activities (Solution Animations) Create/Edit...