Control of fluid flow

Details Control of fluid flow Control of fluid flow

1989-06-27

1990-06-05

Barefoot, Galen

Aeronautics and astronautics

Aircraft sustentation

Sustaining airfoils

244130, B64C 2110

Patent

active

049307290

ABSTRACT:
To modify a turbulent boundary layer flow over a surface to reduce its drag, a series of streamwise riblet projections is provided on the surface arranged in a pattern consisting of spaced large height projections between which are a plurality of smaller height projections. The latter inhibit turbulent eddy motions from penetrating deep into the grooves between them and so displace the turbulent motion away from the wall. The larger projections control the longitudinal vortices or streaks that are characteristic of turbulent boundary layer flow and promote energy transfer to the smaller scale secondary vortices associated with the smaller projections. In another configuration the projections are arranged in a repeated spanwise pattern in which the adjacent projections in each pattern repeat project to different heights, the different heights being so scaled in relation to each other and to the boundary layer thickness that the displacement of the turbulent motion away from the surface by the smaller height projections is extended further by the larger height projections. A further possibility lies in increasing the heights, and possibly also the pitches, of the projections progressively in the downstream direction to mitigate the self-limiting effect of the projections as they establish a raised virtual wall surface for the turbulent boundary layer, the increase being made, continuously or in one or more steps.

REFERENCES:
patent: 208211 (1878-09-01), Swasey
patent: 4650138 (1987-03-01), Grose
patent: 4706910 (1987-11-01), Walsh et al.
patent: 4786016 (1988-11-01), Presz, Jr. et al.
AIAA'83--AIAA-83-0227, Turbulent Drag Reduction for External Flows, D. M. Bushnell, p. 6, lines 16-64.
Mechanical Engineering, vol. 103, No. 3, Mar. 1981, p. 71, Grooves Reduce Aircraft Drag.
AIAA-83-0230--An Experimental Study of Changes in the Structure of a Turbulent Boundary Layer Due to Surface Geometry Changes; Hooshmand et al., Jan. 1983.
AIAA 12th Aerospace Sciences Meeting--Turbulent Boundary Layer Drag Reduction Using Riblets; Walsh, Jan. 1982.
AIAA 22nd Aerospace Sciences Meeting--Optimization and Application of Riblets for Turbulent Drag Reduction; Walsh et al., Jan. 1984.
ICAS '86--Paper No. 86-1.8.3--Drag Reduction Mechanisms Derived from Shark Skin; Bechert et al.; Sep. 1986.

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