Internal cooling of gas turbine engines is achieved by bleeding air off from various compressor stages and delivering it, via a complex network of flow passages, to the desired location. In modern gas turbines the air bled off for such purposes may account for up to 20% of the core airflow and is controlled by static and rotating restrictions such as orifices and seals. As this secondary air makes no direct contribution to engine thrust, there are strong economic incentives for acquiring a detailed knowledge of the flow characteristics of such devices under engine operating conditions, so that secondary air consumption can be minimised. In the present work the behaviour of secondary airflow through radial drillings in concentric shaft assemblies undergoing co- and contra-rotation is investigated using CFD techniques. The results of this work compare well with previously published orifice flow data and provide qualitative and quantitative information on these complex flows to support future air system component design.

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