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