WAVE DRAG REDUCTION CONCEPTS FOR TRANSSONIC WINGS

Abstract

On a typical transsonic transport-type aircraft, wave drag is only a minor component of the total drag at cruise speed compared to viscous drag and induced drag. It is, however, critical for the design since the sharp drag-rise with increasing Mach number basically limits the maximum economic cruise speed of an airplane. The cause of wave drag are the strong shocks developing on the upper side of the wing creating an increase in entropy as well as an increase in boundary layer thickness eventually leading to separation. Different approaches to reduce wave drag have been investigated. One possibility is to change the chordwise pressure distribution such that the formation of strong shocks is avoided. This can be achieved either by conventional trailing edge flaps or by trailing edge modifications such as Gurney flaps or Split flaps. Another option is to reduce shock strength directly by local interaction. This can be realized by spanwise slots or perforated skins or, much more e±ciently, by spanwise contour bumps, as has been successfully demonstrated in a number of research projects. More recently, also three-dimensional devices have been investigated. They promise similar drag reduction potential while being less constrained in the exact position for optimal performance. Streamwise slots and grooves, spikes and D-Strips have been tested. The paper gives an overview of the di®erent approaches to reduce wave drag with an attempt to show the different working mechanisms and benefits.