Control Effectiveness of Vortex Generators in High‐Speed Flows in Off‐Design Conditions

ABSTRACT In aerospace transportation and propulsion systems, shock‐induced flow separation has strong detrimental effects on the aerodynamic behavior and performance. To alleviate these effects, separation control is necessary. A commonly pursued approach uses vortex generators (VG) of different design to increase the momentum transfer within the boundary layer and thus make it less prone to separation. Different mechanical vortex generators, valued in aerospace engineering for their robustness and simplicity, as well as the more flexible and less drag‐penalty prone air‐jet vortex generators (AJVGs) have been studied. A large number of parameters influence the control effectiveness of these devices, amongst them geometrical parameters, flow parameters, and the array arrangement of multiple devices. The latter aspect is particularly relevant for AJVGs, which are small enough to allow for inter‐device spacings that enable interactions between the turbulent structures induced by neighboring AJVGs, and where the intensity of these interactions strongly influence the control effect. With this great number of control parameters, vortex generators may easily encounter off‐design conditions in engineering applications, where operating conditions vary and are not as clean as in a laboratory. An overview on the relevant control parameters is provided, both for mechanical vortex generators including microramps and microvanes and for air‐jet vortex generators. Then, influences of off‐design conditions are discussed on the basis of results from recent experimental and numerical studies. A joint analysis of this rich data set allows an in‐depth interpretation of observed flow phenomena and control effects. Finally, we assess the application potential of the investigated control devices.