Upstream-propagating potential disturbances interacting with a compressible cascade

Phase-locked, unsteady surface-pressure measurements were made at eight suc tion-side and six pressure-side chord locations on the turning vanes of a c ompressible cascade. Cascade inlet Mach numbers ranged from 0.427 to 0.500, resulting in a maximum local Mach number through the cascade vane row of 0 .730. Unsteady forcing of the cascade Has obtained by von Karman vortex she dding from a row of five circular cylinders positioned 0.80 vane chords dow nstream of the cascade trailing edge. The resulting measured surface pressu res were found to be on the same order of magnitude as those measured previ ously in forward-forcing studies, in which the circular cylinders were plac ed 0.80 vane chords upstream of the vane-row leading edge, Frequency decomp osition of the rearward-forced surface-pressure signals provided for the co nstruction of disturbance position-vs-phase maps, allowing the measured dis turbances to be unambiguously interpreted as potential in nature, originati ng at the forcing cylinders, and propagating upstream through the vane row at acoustic speeds. The effect of these potential disturbances on the vane- row pressure response was to elicit two, previously unexpected amplificatio n mechanisms: a large-magnitude pressure rise near the vane-row trailing ed ge and a Mach-number-related, midchord pressure increase known as acoustic blockage.