On the use of surface porosity to reduce unsteady lift

AIAA 2001-2921ON THE USE OF SURFACE POROSITY TO REDUCE UNSTEADY LIFTAna F. TinettiL Jeffrey J. Kelly:Virginia Polytechnic Institute and Slate University, VCESttampton, VA, 23666Stevcn X. S. Bauer #, Russell H. Thomas _NASA I.angley Research CenterHampton, VA, 23681An innovative application of existing technology is pro-posed for attenuating the effects of transient phenom-ena, such as rotor-stator and rotor-strut interactions,linked to noise and fatigue failure in turbomachineryenvironments. A computational study was designed toassess the potential of passive porosity technology as amechanism for alleviating interaction effects by reduc-ing the unsteady lift developed on a stator airfoil subjectto wake impingement. The study inw_lved a typical highbypass fan stator airfoil (solid baseline and severalporous conligurationsl, immersed in a free field andexposed to the effects of a transversely moving wake. Itwas tbund that, for the airfoil under consideration, themagnitude of the unsteady lift could be reduced morethan 18'7, without incurring signilicant performancelosses.NomenclatureA Cross sectional areaI.E l.eading edgeM I.ocal Math numberRe Reynolds numberSn Strouhal number Sn = {md)/<2=U)T l,ocal temperatureU Frees!ream velocityV Wake translational speedc Airfoil chordcd Airfoil drag coefficientc_ Airfoil lift coefficientcp Airfoil pressure coefficientd Diameter of wake generatorp l.ocal flow static pressures Solidity, secondst timeu l,ocal flow velocity normal to porous surface