Numerical Investigation of the Aerodynamic Behaviour of a Compressor Bleed-Air System

Abstract

In this paper the aerodynamic behaviour of two bleed off-take configurations is numerically investigated. Steady RANS simulations were performed and validated with detailed experimental results, thereby improving the understanding of the flow phenomena in the bleed-air system. Bleed air for cooling purposes is usually taken from the main gas path at several locations inside the compressor. This bleed air system must be designed to extract up to 30% of the primary air mass flow of the core engine. In most of the engine designs bleed air is collected by holes or slots, then led through a manifold and distributed by one or more tubes to the components. The design of the bleed air system is usually facing two competing purposes: (1) a high static pressure recovery through the bleed air system and (2) a low interaction with the main gas path. In this study, two bleed off-take configurations are investigated at several operating points, exit tube numbers and positions. Both designs are axisymmetric slots. The first one is inclined at 90° with respect to the main flow path direction representing the simplest design. The second one is inclined at 45° with a radius on its upstream side to improve the bleeding performance. Inserting a radius and a chamfer in the off-take increases the bleed static pressure but also has a negative effect on the main gas path stagnation pressure losses as it disturbs the corner separation on the suction side of the blade.