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Turbine Research for Aerodynamical Vane-frame Improvements in Advanced Two-spool Arrangements

Periodic Reporting for period 2 - TRAVIATA (Turbine Research for Aerodynamical Vane-frame Improvements in Advanced Two-spool Arrangements)

Reporting period: 2019-10-01 to 2021-02-28

Intermediate turbine ducts (ITD) represent the flow path between the high pressure turbine (HPT) and the low pressure turbine (LPT) of a high-bypass ratio aero engine. Caused by the different rotational speeds of high and low pressure spool, these components have to diffuse and guide the flow safely to a larger diameter without disturbances or boundary layer separations. The large radial offset between in- and outlet of ITDs leads to a pronounced S-shape. The trend for further increased bypass ratios will require more attention to this component since its shape influences the overall weight of engine and nacelle considerably. The complicated aerodynamics of these ducts has to be understood to realize shorter designs.
The design of ITDs with integrated flow turning aerofoils (so called TMTF or TVF configurations) has recently received a considerable amount of attention with the introduction of the geared turbo fan (GTF) engine architecture, in the Austrian research landscape, in the broader European environment, and world-wide. In Pratt & Whitney’s new engine family this type of ITDs has been applied for the first time in a serially produced commercial aero engine. It has been demonstrated that the first LP vane row downstream of the TVF can be completely avoided thus decreasing weight, costs and fuel burn.
The GTF is one approach to realize future engines, where the ITD is characterized by smaller radial offsets, counter-rotating HP and LP shafts and faster high-speed LPTs. Equipped with a unique test turbine facility, Graz University of Technology has been at the forefront of European research and development of turbine intermediate duct aerodynamics going back 10-15 years and has also contributed in the testing of different TMTF developments.
In the aerodynamics of TVF modules the interaction with the HPT and LPT rotor is one of the major key factors for loss generation and has to be accounted for already in the design process. The TVF inlet flow is driven by the HPT flow effects including wakes, secondary flow effects and tip leakage as well as purge flows. In order to provide relevant test data to guide the TVF aerodynamic design, it is critical that engine-relevant TVF inlet and exit flow conditions are provided.
Therefore the main objective of the project TRAVIATA is to execute rig tests of TVF aerodynamic designs, coupled with an upstream HPT stage and downstream LPT blade, in a flow environment representative of future GTF aero-engine applications. Since the performance of any HPT-LPT transition duct is impacted by the level of the incoming flow effects, a variation of HPT tip gap and purge flow levels is planned. The aerodynamic performance of the TVF is also affected by the downstream LPT rotor.
The two-spool transonic test turbine facility at TU Graz equipped with a secondary air system (SAS) will be used for performing these investigations. Besides conventional measurement with rakes and pneumatic probes advanced instrumentation such as fast response pressure probes, optical measurement techniques as well as concentration measurements will be used. In this way not only the pure component performance, such as pressure loss, will be evaluated but also the unsteady three-dimensional interaction between the neighbouring components. With the help of the SAS the influence of different independent purge flows and their variations onto the TVF aerodynamics will be investigated for the first time.
The improved understanding of the flow effects can then guarantee that a rise in technology readiness level from TRL4 to TRL5 will be possible and that the input for a Ground Test Demo (TRL6) can be provided.
The first part of TRAVIATA was used to perform all the work which was necessary to prepare for the test campaigns of the two different TVF setups. Also the operating conditions were chosen in close cooperation in order to ensure save rig operation with avoiding any risks. To guarantee this it was found that a new suction blower in the exhaust line of the test facility is needed. TU Graz was in charge of the selection, the procurement and the implementation of this device. A radial blower with a power of 560 kW has been selected.
To be able to measure the power of the downstream LPT very precisely it was necessary to equip the test turbine with a torquemeter flange between LPT rotor disc and LPT shaft. Only in this way the tare losses of bearings and seals are not included in the measured torque. The new torquemeter was specially developed to provide high precision together with enough stiffness to ensure save rig operation in terms of rotordynamics.
During the layout it turned out that exactly for this save operation an increase of bearing stiffness was necessary due to a larger disc overhang and enhanced operating speeds of such a desired high-speed LPT. The solution was to design and manufacture a new bearing cartridge for the rig with a preloaded bearing arrangement and better seals.
TU Graz was also in charge of the rig instrumentation and all the necessary test preparations. It has to be mentioned that additionally the concentration measurement technique will be applied within TRAVIATA to enable the detailed study of the interaction between main and purge flow. Therefore the test facility was also adapted in terms of seed gas insertion and the test hardware with arrays of surface taps.
Due to a priority change and delays by the topic manager the scheduled testing slot for Test 1 was missed. A main task of the second reporting period TU Graz was the installation of the new bearing cartridge together with the torquemeter and the suction blower and the commissioning of these equipment. The finalization of the rig adaptations for the seed gas test hardware was realized as well. As planned all preparations for Test 2 have been done including assembly, instrumentation and commissioning. At the moment at TU Graz a prolonged seven-month testing period of setup 2 is ongoing. The experimental campaign uses as planned conventional but also additional new advanced measurements techniques such as a Two-Sensor-FRAPP and concentration measurements with seed gas in order to track the path of purge air through the duct and study their interaction with other components.
Within the Clean Sky 2 program, significant steps towards the reductions in fuel burn, emissions, and perceived noise are targeted for the aviation sector (75% reduction in CO2 emissions, a 90% reduction in NOx emissions and a 65% reduction of the noise compared to a reference of 2000). The Ultra High Propulsive Efficiency (UHPE) engine concept requires the development of new technologies for geared aero engines planned to be introduced into the market around 2025. TRAVIATA is intended to make valuable contributions to this goals.
The project will enable TU Graz to continue the research work on intermediate turbine structures. In combination with already executed projects it will improve the expertise of TU Graz and strengthen the position as valuable strategic partner for the aeronautical industry.
Two PhD positions are provided over the whole scheduled timeline. Therefore not only the topic manager and TU Graz benefits from Clean Sky 2. Also the community will gain general new insights through these doctoral theses and the related publications. This will support TU Graz known as attractive employer for scientific personnel such as post-docs and PhD-students.
Logo of the Project Traviata
New LP Shaft with Torquemeter
Inspection of Rotor Assembly
Laser-Sintered Kiel-Head Rake
Test 2 Setup Mounted in the Test Facility