Mathematical developments regarding boundary layer theory during the last 25 years

The advances in boundary layer theory made within the last 25 years are considered in the context of the general development of this theory, taking into account also aspects of expected future developments. The characteristics of a boundary layer are examined and boundary layer flows are discussed. A description is given of the boundary layer theory, as first conceived by Prandtl (1904). In a review of the results obtained during the last 25 years, attention is given to the method of differential inequalities, the external boundary condition, questions concerning the existence of a solution for the boundary layer equations under the given boundary conditions, aspects of uniqueness and continuous dependence on the data, asymptotic considerations for disappearing viscosity, approaches for obtaining approximate solutions for the Prandtl boundary value problem, and a priori estimates. A number of problems which have not yet been solved are also discussed.