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The Precessing Vortex Core (PVC) is a coherent structure that can arise inswirling jets from a global instability. In this work, the PVC is investigatedunder highly turbulent conditions. The goal is to characterize the receptivityof the PVC to active flow control, both theoretically and experimentally. Basedon stereoscopic particle image velocimetry and surface pressure measurements,the experimental studies are facilitated by Fourier decomposition and properorthogonal decomposition. The frequency and the mode shape of the PVC areextracted and a very good agreement with the theoretical prediction by globallinear stability analysis (LSA) is found. By employing an adjoint LSA, it isfound that the PVC is particularly receptive inside the duct upstream of theswirling jet. Open-loop zero net mass flux actuation is applied at differentaxial positions inside the duct with the goal of frequency synchronization ofthe PVC. The actuation is shown to have the strongest effect close to the exitof the duct. There, frequency synchronization is reached primarily throughdirect mode-to-mode interaction. Applying the actuation farther upstream,synchronization is only achieved by a modification of the mean flow thatmanipulates the swirl number. These experimental observations matchqualitatively well with the theoretical receptivity derived from adjoint LSA.Although the process of synchronization is very complex, it is concluded thatadjoint LSA based on mean field theory sufficiently predicts regions of highand low receptivity. Furthermore, the adjoint framework promises to be avaluable tool for finding ideal locations for flow control applications.

Receptivity of the turbulent precessing vortex core: synchronization experiments and global adjoint linear stability analysis