简介：Inthemidseventiesanewpropulsorforaircraftwasdesignedandinvestigated-theso-calledPROPFAN.Withregardtothetotalpressureincrease,itrangesbetweenaconventionalpropellerandaturbofanwithveryhighbypassratio.Thisnewpropulsionsystempromisedareductioninfuelconsumptionof15to25%comparedtoenginesatthattime.Alotofpropfans(HamiltonStandard,USA)withdifferentnumbersofbladesandbladeshapeshavebeendesignedandtestedinwindtunnelsinordertofindanopimuminefficiency,Fig.1.ParalleltothisdevelopmentGE,USA,madeadesignofacounterrotatingunductedpropfan,theso-calledUDF,Fig.2.Aprototypeenginewasmanufacturedandinvestigatedonanin-flighttestbedmountedattheMD82andtheB727.Sincethattimetherehasnotbeenanyfurtherdevelopmentofpropfans(exceptAN70withNK90-engineUkraine,whichismoreorlessapropellerdesign)duetorelativelylowfuelpricesandtechnicalobstacles.Onlytechnicalprogramsindiferentcountriesarestillgoingoninordertoprepareadatabasefordesigningcounterrotatingfansintermsofaeroacoustics,aerodynamicsandaeroelasticities.InDLR.Germany,alotofexperimentalandnumericalworkhasbeenundertakentounderstandthephysicalbehaviouroftheunsteadyflowinacounterrotatingfan.