The Aeronautical Journal May 2025 Vol 129 No 1335

A major research focus of the Institute of Propulsion Technology at the German Aerospace Center (DLR) is increasing engine compressor efficiency. In this context, the intermediate compressor duct (ICD), which connects the low-pressure compressor (LPC) with the high-pressure compressor (HPC) in a civil jet engine is of eminent significance. Current research at DLR is therefore aimed at taking account of the interaction between the three compressor components, particularly under transient operating conditions, and at reducing the length of the ICD. A shorter ICD is lighter and thus contributes to a lower environmental impact from jet engines. In recent years, extensive test campaigns have been carried out on the specially designed ICD test rig. The limit of possible length reduction was determined. Beyond this limit, the ICD is susceptible to severe detachment at the hub, resulting in high pressure losses.

The implementation of flow control offers the possibility of suppressing the strong separations and allows a further length reduction beyond the separation limit. A new test case has been developed to investigate active and passive flow control in an ICD. This test case is characterised by a particularly strong hub separation which should be suppressed by flow control.

The paper, On the performance of highly aggressive inter compressor ducts, describes the design objective and the design process of the new test case. Furthermore, the performance of this unique ICD is investigated at several typical engine operating points using computational fluid dynamics (CFD) simulations. It is shown that the structure of the ICD flow field depends only on the inlet Mach number and not on the Reynolds number. A sensitivity study of a change in the operating point of the upstream LPC also showed that the ICD is susceptible to choke when the inlet Mach number increases slightly. Therefore, the smallest area of a new ICD should be chosen in such a way as to avoid chocking under off-design conditions. Finally, correlations for determining off-design performance during preliminary design were used to evaluate their application for highly aggressive ICD. The correlations are in a very good correspondence with the numerical simulations.

The test case presented is currently being set up for validation at the DLR ICD test facility in Cologne. Firstly, the performance of the ICD will be investigated to experimentally confirm the results of this paper. Secondly, pulsed jet actuators will be implemented at the ICD hub to suppress separation.

The paper On the performance of highly aggressive inter compressor ducts by S. Fritz, A. Hergt, D. Bresemann, M. Eck and D. Peitsch appears in Volume 129 Issue 1335 of The Aeronautical Journal and is available open access.

The Aeronautical Journal has, for over a century, been the UK’s leading scientific and technical aeronautics Journal and is the world’s oldest Aerospace Journal that remains in production. Published monthly, The Aeronautical Journal draws upon the expertise and resources of The Royal Aeronautical Society providing a world-wide forum for authors from the UK and overseas. Research papers are solicited on all aspects of research, design and development, construction and operation of aircraft and space vehicles. Papers are also welcomed which review, comprehensively, the results of recent research developments in any of the above topics.

The Royal Aeronautical Society is the world’s only professional body dedicated to the entire aerospace community. Established in 1866 to further the art, science and engineering of aeronautics, the Society has been at the forefront of developments ever since.

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