INVESTIGATIONS OF EFFECTS OF SURFACE TEAIPERATURE AND SINGLE ROUGHNESS ELE3IENTS ON BOUlWARY-LATER TBLYSITION

The laminar boundary layer and the position o j the transit l vn point xcre inzedigaied on a heated $at plate. I t was fuund thaf the Reynolds nxrnber of transition decreases as the ttmperature oj the plate i s increased. I t i s shuwn from simple qualitatire analytical considerations thaf the e#mt of rariable ~Gscosity in the bvundary laycr due to the temperature di8erence produces a relocity projfle with an injlection point if the wall temperature i s higher than the free-stream Scrnperature. This p~?file i s conjirrned by measurements. Further~riorc, it i s conjirrned thcf , tren with large dcriation Jrom the Blasius condition, the relocity and tcrnpcrature proJiles are rcry nearly iderrtical, as predictable theoretically for a Prancltl nurn6er u o j the orcl~r of 1.0 Cfor air, (r=0.76). The instability of injection-point pro$les i s discussed. Studies qf the $ow i n the wake oJ large, twodimensional roughness elcrnents are presented. It isshown ihaf a boundary laysr can separate and reaffach ifselJ fo fhc wall &ihouf har-ing transifion take place.