[en] Applications in which airfoils operate under transitional flow conditions are widespread, comprising micro- and nano-aerial-vehicle wings, portions of mid- and large-scale wind-turbine blades or turbomachinery vanes. The paradigm of the renewables, among which wind energy stands as one of the major sources, or the ever-growing use of MAVs for new transportation and delivery modes, field monitoring operations or rescue missions alike, are indicative of the relevant role that transitional flows are acquiring within aerodynamics. Beyond the interest that such applications may have, the scientific contributions of this work are focused on performing an experimental-numerical characterization of airfoils under different flow conditions. Thus, the goals of the study are headed in two directions: on experimental grounds, it aims at complementing the understanding about how transitional conditions influence the characterization and design process of an application-oriented airfoil. This is done by undertaking wind tunnel tests in configurations that attempt to reproduce an ever-more realistic set of flow conditions. The starting point corresponds to the clean-flow paradigm, in which the aerodynamic characterization is performed under a uniform, steady and two-dimensional flow. Then, real effects are introduced either in the flowfield or in the geometry of the airfoil. These two constitute the turbulent- and rough-flow paradigms respectively, and lead to pseudo-real conditions that contrast significantly with the clean configuration. The real-flow paradigm is obtained by combining those two pseudo-real effects, and the behaviour of the airfoil is shown to differ substantially from the previous flows. The characterization process is complemented by an analysis of a discrete-roughness-based flow-control technique that aims at improving either the lift or the efficiency of the airfoil. As occurs for the characterization itself, the flow paradigm is shown to affect the suitedness of the roughness elements for enhancing the aerodynamic behaviour. In fact, it is proven that certain discrete roughness distributions downgrade the aerodynamic behaviour under clean or pseudo-real configurations, but improve it when imposing real-flow conditions. On numerical grounds, two-dimensional RANS simulations and potential-flow-based panel-method calculations are performed under clean- and turbulent-flow configurations. The comparison with their experimental counterparts shows that further advancements are required in turbulence modelling for obtaining acceptable experimental-numerical matches.

[eu] Fluxu-erregimen trantsizionalean lan egiten duten profil aerodinamikoez baliatzen diren aplikazioak ugariak dira, mikro- eta nano-aero-ibilgailuetako hegoak adibidez, edota eskala ertain nahiz handiko aerosorgailuen palak eta turbomakinaria anitzeko alabeak, besteak beste. Berriztagarrien paradigma, zeinaren baitan energia eolikoa iturri nagusienetako bat den, ala drone bidezko garraio eta banaketa-lan modu berriak, eta landa-eremuen monitorizazioa nahiz erreskate misioak azkartzeko berauek duten ahalmena, fluxu trantsizionalek aerodinamika arloan duten garrantziaren seinale dira. Aplikazio horiek piztu dezaketen interesaz haratago, azterketa honek ardatz dituen ekarpen zientifikoak profil aerodinamikoen karakterizazio esperimental-numeriko baten oinarritzen dira, zeinak fluxu baldintza desberdinak aintzat hartzen dituen. Hala, bi ipar bereiz daitezke ikerketaren helburuak sailkatzerako orduan: alor esperimentalean, xede nagusia fluxu trantsizionalen gaineko ezagutza osagarritzea da, fluxu horiek aplikazioetara bideraturiko profilen karakterizazio eta diseinu prozesuak nola baldintzatzen dituzten zehaztuz. Horretarako haize-tunel bidezko testak burutu dira, gero eta errealagoak diren fluxu-baldintza desberdinen pean eginikoak. Lehen baldintza sorta fluxu-garbi deituriko paradigmari dagokio, zeinetan karakterizazio aerodinamikoa baldintza uniforme, egonkor eta bidimentsionalean burutzen den. Ostean, efektu errealak bi modutan txertatzen dira, hots: fluxu-eremuan eta profilaren geometrian. Hala lorturiko konfigurazioei fluxu-turbulentu eta fluxu-zimur paradigmak deritzaie hurrenez hurren, eta baldintza garbiekiko aldaketa nabarmenak eragiten dituzten baldintza pseudoerrealak dira. Fluxu-erreal paradigma bi konfigurazio pseudoerreal horiek uztartuz lortzen da, profilaren jarrera erabat itxuraldatzen delarik. Karakterizazio prozesu hau zimurtasun elementu diskretuen bidezko fluxu-kontrol teknika baten analisia burutuz osagarritu da, profilaren lift indarra nahiz efizientzia hobetzea helburu dituena. Karakterizazioarekin gertatzen den antzera, fluxu-paradigmak berebiziko garrantzia agertzen du kontrol teknikak jarrera aerodinamikoa hobetzeko duen eraginkortasunean. Izan ere, badira baldintza garbi zein pseudoerrealetan jarrera hori okertzen duten elementu diskretuen distribuzio batzuk, paradigma errealera pasatuz gero onurak dakartzatenak. Numerikoki, RANS bidezko eta kodigo potentzialetan oinarritutako simulazio bidimentsionalak burutu dira, konfigurazio garbi eta turbulentuetan. Beraien baliokide diren datu esperimentalekin alderatzean, turbulentzia eta trantsizio prozesuen modelizazio numerikoak hobekuntza nabarmenak behar dituela ondorioztatzen da, onargarriak diren berdintze esperimental-numerikoak lor daitezen.