Experimental Investigation of the Performance of Different Bleed Air System Designs

Abstract

Increasing the turbine inlet temperature to improve thermal efficiency and thus reduce fuel consumption can only be achieved with an optimal supply of cooling air to control the temperature of the turbine blades. The aim of this study is the optimization of bleed air off takes and the reduction of losses caused by the interaction between bleed air and main gas path. Bleed air for cooling purpose is taken from the main gas path at several locations inside compressor by means of the bleed air system. This system must be designed to pick up to 15% out of the primary mass flow through the engine core. In most of the engine designs bleed air is collected by holes or slots, then lead through a manifold and distributed by one or more tubes to the components. The critical features are perturbations in the main gas path and pressure losses in the bleed system. Several bleed air system designs are currently in use, each of them causing specific aerodynamic and thermal perturbations which can reduce the overall efficiency of the compressor stage and even lead to thermal distortions in the casing of the compressor and thus reducing the expected life time of the engine component. To study the efficiency of several bleed air systems a combined experimental and CFD effort was initiated in the framework of the EU project MAGPI. To perform experimental tests, an annular but nonrotating rig has been built at the ITS based on designs chosen by means of CFD studies. The new rig has a modular structure so numerous variation of geometrical und fluid parameters could be studied: different bleed mass flows (4, 9, and 12%), bleed inlet designs, exit tube number and position as well as swirl in the main gas path. First results including pressure losses and flow pattern in the test section will be presented and discussed to improve the understanding of bleed flow systems and to provide a comprehensive data base for validation of CFD methods in engine development.