To reduce the environmental impact and enhance the overall efficiency of an aero engine, both its propulsive and thermal efficiencies need to be increased. A propulsive efficiency improvement can be achieved by increasing the aero engine bypass ratio, while its thermal efficiency can be improved by applying higher turbine entry temperatures and higher overall pressure ratio cycles. Therefore, the research activities of FloCoTec are associated with the development of novel high pressure compressor (HPC) rear stage concepts to achieve a high overall pressure ratio within the engine core. However, a further increase in core engine pressure ratio leads to an inevitable reduction of the core engine size and cross sectional area, which introduces new HPC design challenges, particularly for the compressor rear stages. Since the rotor tip and stator seal clearances are limited on an absolute scale to avoid rubs, a decrease in blade height results in larger relative blade clearances, which lead to increased secondary flow phenomena, including stronger blade tip vortices, shroud leakage flows, and an increased boundary layer growth in the endwall regions. These detrimental aerodynamic effects penalize the operational behaviour (stall margin) and aerodynamic performance (efficiency).
To overcome the detrimental effects arising from pronounced rotor tip leakage flows, casing treatments (CT) are commonly applied. However, while CTs are known to strengthen the flow in the rotor tip region, they typically cause a radial re-balancing of the flow and weaken the downstream compressor flow at lower span heights. This phenomenon will be particularly pronounced within the compact rear stages of future high-pressure ratio HPCs with small blade heights, and considerably increases the risk of a premature compressor stall due to weaker flows at lower span regions.
To tackle these aerodynamic challenges, GEDE investigates innovative HPC technologies including an advanced 3D blade design for HPC rear stages within CS2 Joint Undertaking. TUM aims to contribute to the research of GEDE through:
OB 1. The development of compressor flow treatment technologies that strengthen the flow across the entire span, enhance the stability in a multi-stage compressor environment, and maximise the potential of the CT-technology. The aim is to deliver an efficiency-neutral HPC rear stage design with an increase of compressor stall margin by ≥ 5%.
OB 2. The provision of a compressor rig test facility that allows for a validation of the HPC rear stage technologies developed by GEDE and TUM, including a detailed quantification of the HPC performance and operability, under engine representative conditions.
OB 3. The development and application of advanced unsteady pressure and temperature measurements that allow for a time-accurate entropy estimation and thus provide a detailed understanding of the flow physics and aerodynamic loss mechanisms within the developed HPC rear stage concept.
The numerical reaearch activities provided a novel flow treatment concept, which counteracts the radial rebalancing effect caused by the CT. The novel FT concept of CT plus blowing type FT lead to an efficiency neutral HPC rear stage concept with a stability increase of more than 10%. Thus, objective OB1 could be fulfilled and the expectations were exceeded. The experimental work provided a compressor test rig HPC rear stage technologies developed by GEDE. With the aid of the rig, the HPC concept's performance and operability, under engine representative conditions could be quantified and OB2 was fulfiled. The applied advanced unsteady pressure (FRAP) and temperature (hot wire) measurement probes allowed for a time-accurate entropy estimation and the fulfillment of OB3. Hence, all objective of the projects were met.
