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