GALCIT Colloquium

Wall-bounded turbulent flows are complex even in canonical geometries and flow acceleration further complicates their physics. In this talk, we discuss novel experimental facilities that enable the systematic characterization of complex pressure gradient and curvature effects, including variable spatial and temporal history. The experiments are carried out using a variable-positioned ceiling and are measured using time-resolved, planar particle image velocimetry and pressure transducers. Statistical results are shown for both statically held and dynamic pressure gradients. History effects (prior pressure gradients imposed upstream of the position of interest) and dynamic effects (a dependence on the rate of pressure gradient imposition) are both observed. The formation of an internal layer is identified for stronger but not weaker static pressure gradient variations, yielding distinct downstream boundary layer evolution. Dynamically applied pressure gradients demonstrate weaker internal layers. Spectral and modal representations of the flow for stationary and dynamic flow cases are compared. Spectral and space-time proper orthogonal decomposition are discussed and leveraged.