 determin turbul skin friction pitot tube determin turbul skin friction pitot tube simpl method determin local turbul skin friction smooth surfac develop utilis round pitot tube rest surfac assum exist region surfac condit function skin friction relev physic constant fluid suitabl length univers non-dimension relat differ total pressur record tube static pressur wall term skin friction relat assumpt independ pressur gradient truth form relat establish consider degre accuraci pipe geometr round pitot tube--the diamet repres length pitot tube determin local skin friction coeffici three station wind tunnel wall vari condit pressur gradient station limit experiment accuraci deduc skin friction coeffici pitot tube confirm basic assumpt leav doubt correct skin friction pitot travers pipe boundari layer wind tunnel wall plot non-dimension form basi suggest fell close region outer limit repres breakdown basic assumpt close wall spread unknown displac effect centr pitot tube wall evid exist region local dynam similar correct skin friction deduc measur round pitot tube wind tunnel wall extent region local dynam similar expect hold appear vari boundari-layer thick condit remot close separ 