Three ways rotation shifts an acoustic black hole's shadow

Acoustic black holes are vortex flows in fluids where sound rays mimic light near a real black hole. By ray-tracing null acoustic paths through a rotating 'draining-bathtub' flow, the authors identify three clean observational handles: a shadow centroid that shifts linearly with circulation, a left-right redshift tilt, and a branch-dependent flux imbalance. Total flux is a poor diagnostic of rotation, but these differential quantities could guide tabletop experiments seeking to probe the acoustic analog of frame-dragging.