Eustace RM & Barrett RV (U of Bristol).
The use of suction to suppress disturbances in laminar flow caused by insect and other surface debris
Publication: Proceedings of Institution of Mechanical Engineers, vol 213,Part G., pp. 277 - 292
Aircraft that employ extensive laminar flow for drag reduction need measures to counter the potential breakdown to turbulence caused by surface debris picked up near the ground. Decontamination methods are being developed but may not be suitable where suction through microperforated skins is used to control the flow, owing to the likelihood of hole blockage. This paper examines an alternative, where the existing suction system is used to draw away the developing turbulent wedges behind individual particles, thus providing a degree of tolerance to surface contamination. A wind tunnel investigation was conducted, using a flat plate model with a configurable suction region, to simulate the essential features of the boundary layer on a laminar flow engine nacelle. This enabled the influence of the various flow and geometric parameters to be assessed. The results, taken at Reynolds numbers/m in the range 1.5--4.5 × 10[sup 6], showed that turbulent wedges could be stabilized and removed, but that this required high levels of suction. The attendant increases in drag and suction system power make the method unattractive economically, although this situation would change if the increased suction could be applied only where required. The condition of self-induced transition at high suction flows was also investigated and was shown to limit the speed at which particle-induced turbulence could be suppressed.
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