Discharge Characteristics of Drilled Throttle Orifices in Fibre Reinforced Plastics for an HLFC System

Abstract

A series of test campaigns at DLR's Large Flow Meter (LFM) has been conducted in order to investigate the discharge characteristics of cylindrical throttle orifices, drilled in fibre reinforced plastics, with respect to their diameter and manufacturing imperfections. In hybrid laminar flow control (HLFC) applications following the ALTTA concept those throttle holes interfacing a common plenum to multiple chambers are used to regulate the local amount of suction through the porous wing surface. The work performed aims at the further development and industrialized application of HLFC in an aircraft environment. This question is tackled by the industry-oriented drilling of throttle holes into coupon size flat samples. Drilling parameters allowing a stable and reproducible process were established through optical inspection. The major experimental findings are discussed in this article alongside some general manufacturing recommendations for throttle holes in HLFC applications.