Question Regarding CFD Post results
 

I am using Fluent to simulate wind flow around a block of buildings and have some questions:

1. When I use volume rendering in my model together with clipping planes (ZX) in order to see the wind velocity at different building height, I noticed that nothing shows up at lower altitudes near the ground (1-10m height) even though when I switched to vector, there are many arrows---I assume that the velocity at these heights is close to my minimum velocity (since I am using a 1/7th law UDF to create the inlet wind velocity profile), so they become transparent. Is there a way to inverse the transparency so that my minimum velocity become opaque and my maximum become transparent so that I can get some results near the ground?

2. When I use the vertex vector to show the wind velocity, the density of the arrows change with the altitudes---is it correct to assume that more arrow mean more wind flow? And what does the arrow length mean in this case?

I am fairly new at this whole CFD thing, so any and all replies is very much appreciated.