21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-3.4.4

OBLIQUE GROOVES AVOIDING LAMINAR FLOW SEPARATION ON BODIES IN POSITIVE PRESSURE GRADIENTS

La Roche U., Palffy S.
F.M. Lab HTL Brugg-Windisch, Switzerland

Keywords: oblique grooves, laminar flow separation, positive pressure gradients

A new surface texture consisting of grooves obliquely oriented to the flow direction has been investigated. The experimental results confirm two key characteristics of the arrangement: 1. avoiding separation of a laminar flow in positive pressure gradients up to local Re of < 200, 000. 2. a reduction of surface friction across the texture of over 30% compared to a smooth surface at Re < 100'000. Prior textures for the same problem known are derived e.g. from the dimples on golf-balls such as used in US Patents 5,378,524 and 5,540,406. The actual texture used has its application for local Re <200, 000 down to very low Re-numbers and has a coarse structure of typically some millimeters groove-width. The results of the Fluid Mechanics Lab have been extended and confirmed by an additional investigation at the Lab for Turbomachinery of the Swiss Federal Institute of Technology in Zurich. The theoretical understanding to allow for correct dimensioning of technical applications is presented. I The grooves allow positive pressure gradients below Re <100, 000 and act as a supertripping device on profiles for the turbulent flow regimes beyond.

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