GB610623A - Improvements in and relating to the control of fluid flow along a solid boundary surface - Google Patents

Abstract

610,623. Boundary layer control. GOLDSTEIN, S., RICHARDS, E. J., and PRESTON, J. H. April 11, 1946, No. 11198. [Class 4] A solid surface intended to serve as the boundary of a fluid stream is provided with a transversely-extending slot facing downstream through which fluid may be injected downstream into the boundary layer tangentially of the surface, which is so shaped that the calculated potential flow velocity decreases abruptly in the downstream direction at a position substantially coincident with the slot and not upstream of it, the upstream velocity gradients being such as not to provoke boundary layer separation, means being provided for injecting fluid through the slot into the boundary layer at a velocity not less than that of the outside edge of the boundary layer immediately upstream of the slot. Fig. 4 shows a thick unsymmetrical aerofoil, the section of which is shaped to produce a discontinuity in the velocity distribution over the upper surface at a point 69.1 per cent of the chord from the leading edge, where a spanwise slot S is provided connected to a pump P for injecting air into the boundary layer. The symmetrical aerofoil section shown in Fig. 6 is shaped to produce velocity discontinuities at points on the upper and lower surfaces distant 80 per cent of the chord from the leading edge. Slots S1, S2, in communication with a pump P are located at these points, the upper one S1 being a suction slot and the lower one S2 a discharge slot through which air drawn through the upper slot is injected into the boundary layer on the lower surface. This arrangement may be modified by providing a discharge slot on both the upper and lower surfaces, the air being supplied to the slots through a single branched duct or two separate ducts. Fig. 8 shows the application of the invention to a symmetrical expansion duct with decreasing velocity in the downstream direction, e.g. for a compressor diffuser, in which downstream-facing injection slots S2 are provided in the portions of the wall W where the velocity q changes abruptly. Specification 578,763 is referred to.