strange distribution of velocity field when using O-block mesh in interFoam
 

Hello, foamers!
I am working with modeling a evaporating droplet using modified interFoam, and an O-block like mesh is used. Then I found that the velocity field looked strange，where staggered velocity magnitude occured on droplet surface. The strange velocity is attached below.
I have exclude other possible reasons and use non-modified interfoam to examinate a simpler case where no heat transfer and source term exist with the same mesh. Result kept the same. So I wonder if the problem is caused by such O-block mesh? Does the mesh I used has a terrible quality? Or can't interFoam behave well when using O-block meshes? (my mesh is also attarhed below, together with my fvScheme and fvSolution files)
The problem has bothered me for a long time and I will be VERY VERY grateful for any suggestion offered.