[Paraview] how to visualize velocity field with streamline

[yi mu]

I have a polygonal dataset in vtk format, the polygonal data is defined by points and vertices. The data attributes are: scalars and vectors. I was able to use glyph filter to show the velocities,  but when I tried to use stream tracer, nothing happen, no matter where I seed my streamline.  What  should I do to show the velocity filed  by using the streamline ? 
 
 Any help are appreciated!
 
 YM

 		
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