Hi Soni,
Good day!
You can find the best explaination in any author of Fluid Mechanics book, that is actually a subject for Mechanical Eng'g students(if you are not one).
It was not so long when i took that subject. I am only sure that the discharge part has a eccen. reducer is to reduce the velocity of the fluid for porpuse of reducing the head loss and etc. The suction side has many explaination just like (if bottom flat, then turbulence is generated and bubles appear that may cause to cavitation and etc)... Please reffer to that book i mention, you learn a lot, i my self must take my review.
But I agree with Sir John that this topic is not here to discuss...
Regards!