Compared with {HEAD ~ a flow} without {TAIL ~ a radius}, the backflow bubble 50 is now hugely enlarged 
without
Compared with { HEAD ~ a flow } without { TAIL ~ a radius } , the backflow bubble 50 is now hugely enlarged
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH