Vortex formation downstream of an active vane vortex generator

A blended wing body aircraft, with embedded engine intakes near the wing trailing edge, requires aerodynamic optimisation under flight conditions to ensure satisfactory aerodynamic performance. In such a configuration, the wing surface upstream of the intake is a critical region within which active boundary layer flow control could provide significant benefits. The static vortex generator has additional drag under cruise conditions, but the active vortex generator not have the same issue. If the active vortex generator (VG) were to be utilised, the transient behavior of the flow downstream of the VG following its activation would need to be understood. The active vortex generator concept adopted in the current study is a thin flat blade, inclined at a constant angle to the local flow direction, which can be deployed from its ‘stowed’ (fully retracted position), allowing it to project into the surface boundary layer and operate as a conventional blade vortex generator once fully extended. This study investigates the transient characteristics of the flow structure downstream of the blade during the deployment, using both up- scaled experimental and numerical simulations. The results contribute data to the development of an effective active flow control strategy, enhancing understanding of the flow control techniques. The experimental approach is designed to examine the fundamental characteristics of the transient behaviour and is split into two work-phases. In Phase I, the study is focused on exploring the feasibility of the experimental approach to generate the vortex-forming transient. Phase II involves the use of a scaled-up experiment for a detailed study of the transient flow structure at Reynolds numbers in the range 1500 to 3500, based on local velocities in the boundary layer and the heights of the blade. In the Phase II experiment, a multi-hole pressure probe is used to record the vortex formation and decay characteristics in a given downstream plane. The data show that the vortex development has a nonlinear response to the blade deflection during the blade deployment. This Phase II data is compared to both RANS CFD steady-state simulations and analytical predictions using empirical models under steady conditions. The supplementary study indicates that the vortex-forming process is dependent on the transient nature of the VG blade deployment and cannot be adequately represented by the steady analysis. A key outcome of this study relates to the practical application of vortex movement within the embedded boundary layer as a result of the VG blade deflection. The transient vortex position profile between the stowed (no vortex) and the deployed (steady-state or static vortex) location is very different from that predicted by steady-state modeling. The transient vortex vertical motion causes a smoother local circulation increase compared to the starting vortex, and the nonlinear circulation variations remain independent of blade size effects. Furthermore, the findings presented in this thesis offer insight into active flow control. With continued study, the active blade vortex generator can increase the aircraft's efficiency and performance.