A comparison theorem

The existence of an explosive singularity in the unsteady boundary layer on a rotating disc in a counter-rotating fluid has now been shown incontrovertibly following the work of K. Stewartson, C. J. Simpson, and R. J. Bodonyi (J. Fluid. Mech.121 (1982), 507–515). Here, we develop some asymptotic results for the governing differential equations to help gain an understanding of the mechanism behind this phenomenon. No definite conclusions are possible, but the presence of inertial oscillations at the edge of the boundary layer could well play a definite role.