Measurement and Analysis of the Flowé elds Induced by Suction Perforations

The e ow physics of laminar e ow control suction surfaces is revealed by performing a detailed fundamental experimental investigation of an isolated suction perforation. A unique series of nonintrusive, high-resolution measurements are obtained using a three-component laser Doppler velocimetry system, and experiments are conductedin alow-speed, low-turbulencewind tunnel. Thesuctionperforation e owe eldsaremappedfora rangeof sub-andsupercritical suctionratesandarefoundto behighlythreedimensional.Arich variety ofe owe eld features is observed, including a pair of counter-rotating longitudinal vortices, multiple corotating longitudinal vortices, spanwise variations of themean e ow, and inherently unstable boundary-layer proe les. Critical suction limits, over a range of freestream speeds, are determined, and a new design criterion for critical suction is established. It is also shown that for sufe ciently small perforations, irrespective of suction e ow, boundary-layer transition does not occur. Further analyses of the measurements explore the possibility of interaction between the crosse ow vortices and the suction-induced longitudinal vortices. The suction-induced transition process is discovered to commence with an instability of the longitudinal vortices. Engineering design criteria, i.e., suction limits and perforation spacings, are established. Nomenclature