THE structure of the laminar, time-dependent boundary layer associated with an oscillating velocity owfi eld in cylindrical chambers including steady sidewall injection plays an important role in combustion stability assessments in solid rocket motors. 1–3 Recent numerical solutions, 4–8 cold-ow experiments, 9, 10 and theoretical analyses11, 16 have contributed to the general understanding of the boundary-layer character, which is a constant companion of the velocity fi eld. Traditionally, in combustion stability predictions, the oscillatory velocity is assumed to be irrotational and inviscid with an associated quasisteady boundary layer that is confined to a thin viscous region near the transpiring surface. Computational predictions of the velocity fi eld by Roach et al., 4 and Vuillot and Avalon, 5 and Vuillot, 6 and cold-ow tests by Brown et al., 10 have shown that the rotational region in such ows, sometimes referred to as the acoustic boundary layer, is actually distributed over a signifi cant portion of the chamber radius. Recent analytical and numerical predictions of the transient evolution of the velocity fi eld prescribed by harmonic endwall11 and sidewall12 disturbances have also indicated the important role played by the rotational component of the time-dependent velocity. Flandro, 13–16 using analytical means, attempted several approaches to solve this problem. His first approach used viscosity to explain the damping of shear waves generated at the porous surface. 13, 14 To attain a solution, the axial convection of vorticity had to be sacrificed in the momentum equation. The radial convection of vorticity also had to be approximated. In his second approach, the axial convection of vorticity was included while viscous terms were neglected. 15 In his third approach, all of the important terms in the momentum equation