As part of Clean Sky 2 (Engines ITD), a working group, formed by the DLR Institute of Propulsion Technology, MTU Aero Engines and GKN Aerospace, is setting up a complete compression system module (LPC/ICD/HPC). The aim of the project is to shorten the intermediate compressor duct (ICD), which connects the low pressure compressor (LPC) and high pressure compressor (HPC). This leads to a reduction of the axial length and weight of the overall engine and thus a reduction of the specific fuel consumption. In order to identify measurement-technologies and mitigate risks for this experimental set-up, a non-rotating testrig was set up in advance to investigate two different test vehicles. In a first step an ICD demonstrator was set up, which had a reduced axial length of 25%, compared to currently operating designs. This design predicted no separation or performance losses inside of the aggressive s-shaped contour. In a second step another demonstrator was installed with an even shorter axial length of 50% axial length reduction, compared to todays state of the art configurations. In this demonstrator the design was chosen to exceed the functional limit according to today’s CFD prediction and thus explore the potential for further length reduction in the future and to create a data base for numerical tool validation. The two configurations were tested at DLR Cologne. The test channel offers the possibility to use a variety of different measurement techniques to determine the flow behavior inside the ICD. This paper presents the oil streak pattern taken on the hub area between the struts and the ones taken on the pressure and suction side of the outlet guide vanes (OGV- LPC) for both demonstrators.

Compression systems of modern, civil aircraft engines consist of three components: Fan, low-pressure compressor (LPC) and high-pressure compressor (HPC). The efficiency of each component has improved over the last decades by means of rising computational power which made high level aerodynamic optimisations possible. Each component has been addressed individually and separated from the effects of upstream and downstream components. But as much time and effort has been spend to improve performance of rotating components, the stationary inter-compressor duct (ICD) has only received minor attention. With the rotating compression components being highly optimised and sophisticated their performance potential is limited. That is why more aggressive, respectively shorter, ICDs get more and more into the focus of research and engine manufacturers. The length reduction offers high weight saving and thus fuel saving potential as a shorter ICD means a reduction in aircraft engine length. This paper aims at evaluating the impact of more aggressive duct geometries on LPC and HPC performance. A multi objective 3D computational fluid dynamics (CFD) aerodynamic optimisation is performed on a preliminary design of a novel two spool compressor rig incorporating four different operating line and two near-stall (NST) conditions which ensure operability throughout the whole compressor operating range. While the ICD is free to change in length, shape and cross-section area, the blades of LPC and HPC are adjusted for changing duct aerodynamics via profile re-staggering to keep number of free parameters low. With this parametrisation length, reductions for the ICD of up to 40% are feasible while keeping the reduction in isentropic efficiency at aerodynamic design point for the compressor below 1%pt. Three geometries of the Pareto front are analysed in detail focusing on ICD secondary flow behaviour and changes of aerodynamics in LPC and HPC. In order to asses changes in stall margin, speedlines for the three geometries are analysed.

Reducing the fuel consumption of airplanes is one of the main research topics of the aero industry. Due to this, the bypass ratio in modern aero engines is increasing and the radial offset between the low pressure compressor (LPC) and the high pressure compressor (HPC) is getting larger. Motivated by shortening the length of the duct between the LPC and HPC, called the intermediate compressor duct (ICD), a workgroup from DLR Institute of Propulsion Technology, MTU Aero Engines AG and GKN Aerospace set up a measurement series in the new DLR ring cascade wind tunnel, that simulates a shorter and therefore aero-dynamically more aggressive s-shaped ICD. The setup consists of a full annulus channel. It provides 60 swirler blades which simulate the last rotor of the LPC, 120 LPC outlet guide vanes (OGV), 10 struts and 30 HPC inlet guide vanes (IGV). The airfoil counts are generic counts proposed for validation. Behind the OGV, there is a bleed air outlet which can be varied between 3% and 35% of the mass flow. This paper describes the highly instrumented test rig and its measurement techniques. We are able to analyze the specific flow behavior as well as determine the main ICD-performance parameter. Seven different measurement planes are located between the mentioned blade rows. The total state and the velocity (absolute value and directions) are among others measured in the plane. For each task and measurement location the best suited measurement method is selected. These are mainly multi hole probes in the main measurements planes, L2F in narrow places. The tests are conducted at eight different operating points, varying in Mach number, Reynolds number, bleed rate, stagger angle of swirler and HPC IGV. The high number of measurements leads to a profound understanding of the behavior of the ICD. The resulting conclusion is that in spite of the reduced axial length the flow through the aggressive s-shape of the ICD no separation occurs and therefore the desired performance is achieved.