an elongated axial core element extending in {HEAD ~ the direction} of {TAIL ~ fluid flow} of the fluid, and 
of
an elongated axial core element extending in { HEAD ~ the direction } of { TAIL ~ fluid flow } of the fluid , and
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH