Visualizing flow instabilities and control mechanisms in 3D cylindrical cavities with a top bounding wall

Cavity flows studied over the past few decades have led to an increased understanding of flow physics and instability modes. Most studies focus on two-dimensional cavities with a limited number on three-dimensional (cuboidal) and a few on cylindrical cavities, using either numerical or experimental techniques. There is, however, a significant variation in the flow with the presence of a top bounding wall, a configuration that occurs most commonly in turbomachinery hole-pattern seals. Recent (detached eddy) simulations by the author revealed 2D and 3D instabilities in such settings akin to shear-layer and wake-mode instabilities in traditional subsonic open cavity flows. The instabilities show modified dynamics accounting for the top bounding wall but similar Rossiter modes as open cavity flows. Mode-switching from the shear-layer mode to the wake mode is also documented and leads to large-scale variations in the drag characteristics of the overall flow. The present study complements the numerical work via smoke flow visualization enabling matched comparisons to the simulations. The experimental setup is updated with two (individual) passive flow control mechanisms designed to prevent instability mode switching. The effect of the flow control devices is qualitatively analyzed via the smoke flow visualizations by altering the operating conditions and the resulting dynamics are used to set up future numerical simulations for parametric studies.