 fundament statist theori turbul fundament statist theori turbul statist theori gener consid valu quantiti case turbul motion interest valu veloc deriv valu squar product veloc deriv reynold express so-call appar turbul stress valu product veloc compon theori suggest common object establish relat valu turbul shear stress product veloc fluctuat deriv veloc measur veloc gradient sort investig concept correl paramount late friedman introduc correl unknown variabl hydrodynam equat carri investig practic compar experiment evid taylor success analysi isotrop turbul correl calcul discuss theoret problem decai turbul windstream turbul produc devic theori rais consider interest concern problem wind-tunnel turbul compar directli experiment work dryden countri fage townend simmon england paper concern fundament problem uniform isotrop turbul turbul friction parallel stream gener theori isotrop turbul develop gener theori includ taylor's consider special case 