Examination of three candidate technologies for high-lift devices on an aircraft wing

摘要

A research programme was initiated to examine three candidate high-lift technologies,which would, if implemented, simplify the mechanical complexity of the multiplecomponent trailing-edge devices traditionally employed on civil transport aircraft.Experimental studies were undertaken with the aim of examining each technology interms of its potential to favourably influence boundary layer development and improve the aerodynamic characteristics of a high-lift configuration.Preliminary studies of triangular serrated geometries, at the trailing edge of a modifiedflat plate, highlighted that the ability of the serrations to favourably influence the flowfield development over an aft positioned single slotted flap was critically dependentupon the flap lap/gap and deflection angle. Under the test conditions, the serrationswere most effective at low flap deflection angles, particularly serrations with a lengthcorresponding to 13% flap chord. Extending these studies to a representative high-liftconfiguration significantly limited the range of flap laps/gaps and deflection angles overwhich the serrations were favourable. Furthermore, oil flow visualisation providedevidence of wake structures emanating from serration vertices, corroborating earlierhypotheses and suggesting the flow mechanism by which serrations favourablyinfluenced boundary layer development over the upper surface of the downstream flap.Experiments indicated that when optimised, blowing tangentially from a slot at thetrailing edge of the main element over the upper surface of a flap within a three-elementhigh-lift configuration, provided a highly effective means of preventing boundary layerseparation and increasing lift. This was corroborated by oil flow visualisation andcomputational simulations. Maintaining the same momentum coefficient and blowingthrough discrete orifices at the trailing edge of the main element, proved highlyfavourable, heightening the increment in lift in comparison to the correspondingtangential slot blowing configuration. Hence, the mass flow rate could be reduced in comparison to the tangential slot blowing configuration, without compromising theaerodynamic performance.