Autor: Thorben Aufderheide

Abstract The secondary air system is an important auxiliary system for safe and stable opera- tions of modern aero engines. To supply internal and external consumers within the secondary air system, bleed air is removed from the primary (core) flow at several locations inside the compressor. The bleed air leaves the core compressor by bleed off-takes on the hub and casing endwalls and high pressure air is supplied for turbine cooling, de-icing, sealing, or cabin air. The bleed mass flow rates vary throughout the flight cycle for each application and can be up to 30% of primary flow. The removal of air from the compressor has a direct impact on the overall engine performan- ce. Therefore, it is important that the off-take configuration is adapted to the flow conditions. Main design criteria for off-take configurations are a high static pressu- re recovery through the bleed air system and a low interaction with the primary flow. In this thesis, experimental and numerical investigations present the interaction bet- ween a bleed air off-take configuration and the core flow of a compressor cascade. The experimental investigations were carried out in a low-speed cascade wind tunnel and the experimental results are supported by numerical simulations. The off-take configuration is a pitchwise-symmetric slot at the endwall downstream of the com- pressor cascade. The effect of bleed air removal on the compressor cascade flow is shown based on bleed flow rates of 4.0%, 7.8% and 14.3% of the core flow. The results show that the secondary air removal induced a redistribution of the cascade flow and has a strong effect on the cascade characteristics. The development of the classical secondary flow is disturbed due to the bleed air removal and parts of the vortices near the endwall are removed by the bleed off-take. The effect of bleed air removal is not only limited to the region near the slot but also is present at the opposite endwall region. Furthermore, this thesis presents the performance of different bleed off-take configu- ration. Based on a datum configuration, the design is adapted to the flow conditions step-by-step. The location and shape of the pitchwise-symmetric slot at the endwall was not part of the modification. The results show that the modification of the bleed configuration increased the static pressure recovery by up to (delta)cp = 0, 17.