Relaminarisation of the Swept Wing Attachment-Line by Surface Suction

Abstract

It is now well established that the leading edge is a critical region for boundary layer transition to turbulence on a swept-back wing. Under the appropriate conditions, transition can occur on the attachment line itself (x=0) and this is particularly important since, in the absence of subsequent relaminarisation, full chord, turbulent flow on both upper and lower surfaces will be produced. It has been demonstrated in previous papers [1,2] that, for an impervious surface, the attachment-line transition process can be instigated at Reynolds numbers which are very much lower than those associated with linear (and non-linear) stability theory. Moreover, there is a very clearly defined lower boundary for the transition Reynolds number in the presence of large forcing disturbances. Large disturbances can take the form of surface roughness or they can emanate from the wing fuselage junction. Under these circumstances the transition process is commonly referred to as “attachment-line contamination” In the context of the laminar flow aircraft, attachment-line contamination is known to be a serious practical problem. Therefore, the determination of the effect of surface transpiration on attachment-line contamination