Numerical Investigation of Vortex Breakdown Control by Along-the-Core Blowing in Transonic Flows

Abstract

Almost all modern combat aircraft use delta wings or multiple-swept delta wings in order to achieve high maneuverability at high speeds. The flow field around these kinds of wings is dominated by strong leading-edge vortices. At low to moderate angles of attack, these vortices contribute strongly to the overall lift of the aircraft. However, at high angles of attack, vortex breakdown occurs, leading to the loss of the corresponding vortex lift and potentially inducing high forces and moments. As these forces and moments influence the stability and control characteristics of the aircraft, it is desirable to control and delay the breakdown of the leading-edge vortices. However, while active flow control for vortex breakdown control has long been studied for subsonic flows, very little research is available concerning its application to transonic flows. The focus of the current study is therefore the numerical investigation of the control of vortex breakdown on the DLR-F23 configuration at two different Mach numbers, Ma = 0.5, 0.85. The DLR-F23 is a eneric multiple-swept wing configuration with leading-edge sweep angles of ϕ1 = 45°, ϕ2 = 75° and ϕ3 = 45°, corresponding to levcon, strake and main wing. The goal of the study is to delay the onset of vortex breakdown of the midboard vortex by using a jet to inject additional axial momentum into the vortex core. It was found that a jet location between the levcon and strake leading-edges was most suitable, as it allowed to introduce the jet in between the separated shear-layers originating from the two leading-edges. With a jet located in this position it was possible to noticeably delay, and in some cases even completely suppress, vortex breakdown over a broad angle of attack range.