Problem with streamlines
 

Hi

I am using acusolve for my project. I am simulating a turbine. The streamlines that I get have some concentric rings in the centre. Could somebody please help me in understanding the meaning of these and how to get rid of them. I have attached an image to show how the streamlines look.

A few different view angles and contours could probably get more attention/ response from the experts here... per my opinion this seems like a cavitation region..why? and how to get rid of them..? hard to deduce as no flow parameters, BCs, conceptual idea is given in your question..