Streamlines 
trace the path of fluid particles through the flow field. They are a useful way to gain a good understanding not just of the values of the variables at each point, but of the overall movement of the flow.
For example, they can indicate where flow might be separating or recirculating.
To create streamlines:
Click the Streamlines icon
in the visualization toolbar. This will open up the tool in the properties panel.Select the desired Streamline Field.
Choose an Integration Direction to control if the particles should move forward, backward, or both.
Set the Maximum Length of the lines to generate. The unit of length matches that of the domain.
Choose a Seed Type.
Set the properties required for your chosen seed type. Each seed type will have its own set of properties. Learn more about each below.
Click the check button to start computing streamlines.
After creating streamlines, use the dropdown menus in the Display section to adjust the appearance of the streamlines.
Note: The maximum number of streamlines per filter is 10,000.
Rake
Place seed particles along a line. You will need to specify:
Start and End points of the line
Number of Streamlines to be generated
Sphere
Place seed particles within a sphere. You will need to specify:
Center of the sphere in Cartesian coordinates
Radius of the sphere
Number of Streamlines to be generated
Grid
Place several rakes parallel to one another. You can view the streamlines from a single rake in the grid, or from every rake in the grid at once. You will need to specify:
Center of the grid in cartesian coordinates
Row Orientation specified as a vector in Cartesian coordinates
Column Orientation specified as a vector in Cartesian coordinates
Number of Seeds (or columns) in the grid
Number of Rakes to be generated
Seed Spacing to determine how far apart each seed is from one another
Rake Spacing to determine how far apart each rake is from one another
After generating streamlines with a grid, you can adjust how many rakes you can see at once by adjusting the slider at the bottom of the properties panel.
Surface
Place particles on the surface of your mesh to trace surface streamlines. You will need to specify the following:
The surfaces you’d like to generate surface streamlines on
Every N Points, or the rate of sampling points on the surfaces you’ve selected
Surface Streamlines will constrain the streamlines to the specified surfaces. The streamlines will only appear directly on the surfaces specified for non-zero vector fields. For example, since velocity at the surface is zero, no streamlines will be produced.
Surface Offset specifies the distance from the seed particles to the surface. The streamlines will trace through the volume.
Note: The maximum number of surface streamlines per filter is 2,500.