Improvements in or relating to fluid-solid contact-surfaces

摘要

578,763. Reducing surface friction between a solid and a fluid. GRIFFITH, A. A. Aug. 25, 1942, No. 11973. [Class 4] To improve the effect of slots provided for the removal by suction of the boundary layer of fluid from surfaces such as those of aeroplanes, pumps, compressors and turbines, that are movable relatively to the fluid, the surface is so shaped that no rise of pressure occurs on the surface in the general direction of flow except in the region between a slot and its associated stagnation point where the flow of the boundary layer is locally reversed in direction. This may be done by providing that the surface curvature suddenly changes in passing across the slot so that it is less convex on the downstream side of the slot. In the example shown, the parts 23, 24 of the surface on the upstream and downstream side of a slot 13 are convex and concave respectively and the slot is tangential to the curve 24. There is thus no rise of pressure except as shown by the pressure curve P at 19, between the slot and the stagnation point 18 and the pressure falls gradually as indicated at 25, from the stagnation point to the next slot downstream. A fan 26 is provided for producing suction in the slots. With a surface and slots so formed and arranged, there is no fall and subsequent rise of pressure between the stagnation point and the next slot such as is shown to exist with the usual slotted surface. In a modification, the slots are wider than is necessary for the removal of the boundary layer and there is a sharp edge between the convex surface 23 and the upper flat wall of the slot.