A boundary-layer collision in a curved duct

It is shown that the boundary layer, generated at the entrance to a curved duct by an incoming flow at large values of the Dean number, develops a collision structure in the neighborhood of the inner wall, after evolving for a finite distance down the duct. This result is not to be anticipated from the results of previous studies of the entry flow nor from theories of the fully-developed flow far down the duct, but it is nevertheless consistent with the precise results obtained to date. The implication of the phenomenon for the subsequent development of the core flow is discussed.