EFFECTS OF SPECIFIC TYPES OF SURFACE ROUGHNESS ON BOUNDARY-LAYER TRANSITION

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1、NATIONALADVISORYCOMMITTEEFORAERONAUTICSWARTIMEREPORTORIGINALLYISSUEDFebruary1946asAdvanceConfidentialReportL5J29aEFFECTSOFSPECIFICTYPESOFSURFACEROUGHNESSONBOUNDARY-LAYERTRANSITIONByLaurenceK.Loftin,Jr.LangleyMemorialAeronauticalLaboratoryLangleyField,Va.^^;-^^

2、»^Jk^#^Ä-v^W^,J8M*'*?&#-•&'*$ffis$s'*•'•*--•-'•"'•-.^--*<*WASHINGTONNACAWARTIMEREPORTSarereprintsofpapersoriginallyissuedtoproviderapiddistributionofadvanceresearchresultstoanauthorizedgrouprequiringthemforthewareffort.Theywerepre-viouslyheldunderasecurityst

3、atusbutarenowunclassified.Someofthesereportswerenottech-nicallyedited.Allhavebeenreproducedwithoutchangeinordertoexpeditegeneraldistribution.L-U831176013648812NACAACRNo.L5329aNATIONALADVISORYCOMMITTEEFORAERONAUTICSADVAN03CONFIDENTIAL-REPORTEFFECTSOF'SPECIFICTY

4、PESOFSURFACEROfOHHESS...ON;iBOUMPARY-LAYERTRANSITION-"•'.ByLaurenceK.Loftin,Jr.:SUMMARY...••Testawereconducted'withtwotypicallovb-dragair-foilsof90-inchchordtodeterminetheeffectsofsurfaceprojections*grooves,andsandingscratchesonboundary-layertransition.TheReyn

5、oldsnumber-atwhichaspanwiserowofcylindricalprojectionswould'causeprematuretransitionwasdeterminedforarangeofReynoldsnumberfromapproximately3x10"to10x10.Datawere'obtainedfor-projectionsofvarioussizesandchordwiselocationsonbothlow-dragairfoils.Theresultswereanal

6、yzedontheassumptionthatthecriticalairfoilReynoldsnumberforagivenprojectionwasafunctiononlyofthelocal-flowconditionsaroundtheprojection.Thisassumptionnegleotedpossibleeffectsoftunneltur-bulence,pressuregradient,boundary-layerReynolds•number,andtheoriginalextent

7、ofthelaminarflow.Thedatacorrelated.onthebasisofthisassumptionwithinarangeofcriticalairfoilReynoldsnumberof±0.5x106andwithinarangeofprojectionheightof±0.002inch.Thetestsofsurfaoegroovesandsandingscratchesindi-cated-that,,fortherangeofReynoldsnumberinvestigated,

8、thelaminarboundarylayerwasmuchless,sensitivetosurfaoe-groovesandsandingscratohes.-than-toprojectionsaboye-thesurfaceiINTRODUCTIONThedevelopmentoftheNACAlow-drag'airfoils,hasaroused