The expansion of a boundary layer about a corner is of primary importance to a near wake flow field. Experimental evidence shows that turbulent boundary layers separate precisely at the corner and methods are available for predicting such an expansion. Inviscid calculations using rotational characteristics have been successfully used. However, one of the simplest techniques of treating the expansion of a boundary layer is the method of isentropic streamtubes. Calculations with such a method may be easily programmed for digital computers or quickly done on an electronic calculator. In this note, results obtained from the simpler streamtube method are compared with results from the more complex rotational characteristic calculations.

The streamtube method assumes that the flow field is isoenergetic, the stagnation pressure is constant along a streamline, and the flow is uni-directional before and after expansion. Obviously, the boundary layer is assumed to expand without interacting with the adjacent supersonic flow. The coordinate system used is shown in Fig. 1. Y is the coordinate normal to the attached flow direction, and W is the coordinate normal to the inviscid jet boundary streamline. The individual streamlines are located in the expanded profile by applying conservation of mass to the streamtubes.