Question

if n rectilinear vortices of the same strength k are symmetrically arranged as generators of circular cylinder of radius a in an infinite liquid

Answer 1

Hallo friend

Rectilinear Motion just means “In a straight line.” - That is the definition of rectilinear -

It’s easier to understand in context - When a car is moving down the street, it’s generally moving in a straight line.

On the other hand, a wheel is moving in a circle - It’s not rectilinear.

I hope it helps