Periodic Reporting for period 3 - FloCoTec (FLOw COntrol TEChniques Enabling Increased Pressure Ratios in Aero Engine Core Compressors for Ultra-High Propulsive Efficiency Engine Architectures)
Berichtszeitraum: 2021-02-01 bis 2022-03-31
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.
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.
The work within FloCoTec covered numerical as well as experimental aspects. The numerical work scope included the development of a blading representative for highly loaded compressor stages as applied in modern aero engine HPCs. The blading comprises high total pressure ratios, high relative rotor clearances, low aspect ratio blades and shrouded stator blade rows. By applying casing treatments and additional blowing type flow treatments the stall margin of the numerically designed HPC could be enhanced by more than 10%. Hereby no efficiency loss substantiated within the numerical simulations. It appears that the additional FT counteracts the radial rebalancing effect caused by the CT and is thus beneficial for the stage behaviour. The experimental work scope covered the preparation of TUM's HSRC test rig for the upcoming test campaigns. The acquisition of advanced measurement concepts to potentially asses the total pressure and temperature with a high spatial and temporal resolution was performed in parallel. By combining the total pressure and temperature measurement results, an estimation of the entropy generation in a test rig is provided. The measurements are in line with the post-test numerical simulation results.
To exploit the research activities in an optimum way, TUM plans to further mature the developed FT concept and to reconsider this in future HPC designs. Furthermore, the gained expertise with regards to high frequency measurements will help TUM and GEDE for future compressor tests in HSRC rig. In that context, TUM and GEDE plan to leverage the novel measurement techniques and support EU researchers by sharing their knowledge base via consultations, publications, etc.
The dissemination of FloCoTec was mainly conducted via three international conference publications and one journal publication. Furthermore, various student theses and jobs helped to disseminate and the progress of the project. Finally, two PhD theses are currently being developed. Hereby, one thesis will focus on the numerical and one on the experimental aspects of FloCoTec.
To exploit the research activities in an optimum way, TUM plans to further mature the developed FT concept and to reconsider this in future HPC designs. Furthermore, the gained expertise with regards to high frequency measurements will help TUM and GEDE for future compressor tests in HSRC rig. In that context, TUM and GEDE plan to leverage the novel measurement techniques and support EU researchers by sharing their knowledge base via consultations, publications, etc.
The dissemination of FloCoTec was mainly conducted via three international conference publications and one journal publication. Furthermore, various student theses and jobs helped to disseminate and the progress of the project. Finally, two PhD theses are currently being developed. Hereby, one thesis will focus on the numerical and one on the experimental aspects of FloCoTec.
TUM and GEDE cooperatively acquired a novel FT concept to complement CTs. The numerically designed FT compensates the radial rebalancing effects in HPCs caused by CTs through an increase of the axial momentum in the hub regions of the compressor. This leads to a strengthening of the flow across the entire span height. The FT therefore leverages the full potential of CTs in HPCs and delivers an efficiency neutral combined FT with a significant stall margin increase. This allows for a further reduction of the core engine size in future engine concepts. Hence, the treatment concept has the potential to eventually enhance the thermal efficiency of future engine concepts and to reduce the environmental impact of aero engines enabling a more environmental friendly air travel. Furthermore, novel unsteady measurement techniques were acquired for the use in TUM's HSRC test rig. By measuring total pressure and temperature at a high spatial and temporal resolution, an enhanced insight in the test vehicle's loss mechanisms can be gained. This will help future compressor designers to establish compressor configurations for modern, eco-friendly aero-engines.