This radius R is selected in such a way that the flow comes into {HEAD ~ contact} with the wall and thus causes {TAIL ~ the swirl coefficient} to increase considerably 
This radius R is selected in such a way that the flow comes into { HEAD ~ contact } with the wall and thus causes { TAIL ~ the swirl coefficient } to increase considerably
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH