It is obtained by adding {HEAD ~ flow diverters} surrounding {TAIL ~ a helicoid structure} with vertical axis 
surrounding
It is obtained by adding { HEAD ~ flow diverters } surrounding { TAIL ~ a helicoid structure } with vertical axis
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH