Separation control with Air Jet Vortex Generator arrays in transonic and supersonic flow

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Shock-induced flow separation strongly influences the aerodynamic behavior of many aerospace applications, from transonic airfoils and supersonic air-breathing propulsion to control surfaces on hypersonic vehicles. The associated highly unsteady flow field can cause inlet instability, as well as buffeting and structural fatigue when pressure oscillations excite a resonant frequency. The importance of these flows in aerospace transportation motivated great efforts to develop methods that reduce the detrimental effects of separation. This Emmy Noether group investigates a promising new technique: air jet vortex generators (AJVGs). An array of small continuous air jets inserts vortices into the boundary layer. The vortices entrain high-momentum fluid and increase turbulent mixing, which reduces separation and controls the associated unsteadiness. AJVGs have many advantages: unlike with boundary-layer bleed, internal mass-flow rates are not reduced. The system is relatively simple, yet more flexible than mechanical devices and can be turned off when not needed, to decrease parasitic drag. Progress has been made in generating the required expertise on AJVG control for 2D shock-wave/boundary-layer interactions (SWBLI). In most applications, however, geometries and SWBLIs are 3D and thus more complex. The mechanisms in 3D SWBLI that are responsive to separation control, as well as effective control mechanisms and parameters, are unclear. In this project phase, we therefore continue the systematic increase in configuration complexity pursued in the overall project: after nominally 2D interactions and the subsequent addition of 3D effects from side walls and curvature, we now analyze separation control with AJVGs on fully 3D SWBLIs, namely swept-compression-ramp interactions, to approach a more general understanding of AJVG control. The core goals of this project phase are to 1) describe the influence of AJVGs on the mean and turbulent flow topology in 3D SWBLI and identify control parameters, 2) understand the effects of AJVGs on the mechanisms of the 3D SWBLI, and 3) develop a suitable control strategy. These objectives are addressed with an approach combining cutting-edge experimental techniques, high-fidelity numerical simulations, and advanced post processing. The stereo-dual particle-image-velocimetry (S-D-PIV) system developed in the previous project phase provides velocity fields that also include temporal information. Large-eddy simulations provide time-resolved flow fields and detailed insights into the air-jet flow. Together with advanced post-processing schemes (inter alia dynamic mode decomposition), the behavior of turbulent structures and the dynamic mechanisms in the flow fields are finally accessible. By contributing to the fundamental understanding of the related complex flows, this Emmy Noether group participates in preparing the ground for new exciting aerospace-transportation concepts and affordable access to space.