The flow surface includes {HEAD ~ a first portion} and a second portion extending downstream from {TAIL ~ the first portion} 
The flow surface includes { HEAD ~ a first portion } and a second portion extending downstream from { TAIL ~ the first portion }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL