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Seeding-Free, Non-INtrusive Aero-engine disToRtion meAsurements

Periodic Reporting for period 2 - SINATRA (Seeding-Free, Non-INtrusive Aero-engine disToRtion meAsurements)

Reporting period: 2021-11-01 to 2022-10-31

Inlet flow distortion is expected to play a major role in future aircraft architectures where complex air induction systems are required to couple the engine with the airframe. The highly unsteady distortions generated by such intake systems can be detrimental to engine performance and were previously linked with loss of engine stability and potentially catastrophic consequences. Industrial testing, currently relies mostly on steady state distortions although, historically, unsteady distortions were acknowledged as equally important. This is partially due to the limitations of intrusive measurement methods to deliver unsteady data of high spatial resolution in combination with their high cost and complexity.

The combination of different types of distortions is expected to have a strong impact on the engine’s stability margin. Therefore, the need for novel measurement methods able to meet the anticipated demand for more comprehensive flow information is now more critical than ever. The main aim of the research programme is to demonstrate Filtered Rayleigh Scattering (FRS) for inlet distortion measurements pertinent to novel aircraft architectures and provide a roadmap for the development and demonstration of an in-flight, FRS-based inlet distortion measurement system. FRS is a non-intrusive, laser-based flow measurement method able to provide simultaneous measurements of velocity, pressure, and temperature across a plane with high spatial resolution without the requirement to seed the flow. Hence, it is a promising candidate for the characterisation of the complex, distorted flows in novel aircraft air induction systems.

SINATRA aims to address the following objectives:

1. Develop and validate up to TRL4 (Technology Readiness Level) an FRS measurement system prototype for time averaged distortion measurements of pressure, velocity and temperature and demonstrate this in representative complex flow environments.
2. Upgrade the above prototype, to demonstrate an unsteady FRS system at TRL 3.
3. Provide a ground test inlet distortion facility that will be available to the whole European aeronautical, industrial and scientific community.
4. Use the experimental data from the time average FRS measurements to characterise the distorted flows pertinent to closely coupled propulsion systems.
SINATRA belongs to the CSJU’s Thematic programmes and as such its demonstrators aim to develop technologies up to a Technology Readiness Level (TRL) 4.
The work comprises two key bodies; the development of a state-of the-art FRS measurement system, and the delivery of a ground test rig able to produce representative complex flows on which the FRS system will be demonstrated. During the first year of the activity significant progress was made in both areas. The state-of-the-art FRS system was specified in detail and two variations have now been put in place and demonstrated on a simplified, canonical flow. Significant contributions linked to the FRS line of sight optimisation using image fibre bundles as well as Machine Learning based calibrations were made which were never shown before. These aspects have increased the productivity of the measurements by over 100 times compared to the conventional application method. The ground based test facility located at Cranfield University was re-designed aiming to enable flexible line of sight for instrumentation integration around the measurement section but also a wide range of convoluted diffuser that would offer variations in complex flow characteristics. Added capabilities include the ability to install very complex diffuser geometries such as double offset, serpentine ducts, the ability introduce prescribed flow profiles at the entry plane of the convoluted diffuser and most importantly the ability to install a high speed electric fan very close to the exit plane of the diffuser to represent the potential, closely-coupled propulsion system installed at this position.
During the next stages of the programme, the FRS system will transferred to Cranfield University for integration around the distortion test rig and demonstration of the capability in representative complex flow domains.
SINATRA is in the process enable the application of Filtered Rayleigh Scattering (FRS) technology for the measurement of distorted complex flows pertinent to air induction system flows or any other internal flow systems aeronautical or otherwise. Furthermore, it will allow the FRS technology to be assessed to a level similar to other non-intrusive technologies currently better mastered within academia and industry such as Stereo Particle Image Velocimetry (S-PIV) or Doppler Global Velocimetry (DGV).

In the context of Clean Aviation programme, FRS measurement capability would be especially applicable to the following air-transport/mobility missions:
o “Disruptive configurations (distributed propulsion, BLI (Boundary Layer Ingestion), aero control)” where the assessment of inlet fan distortions will be paramount in future eco-efficient designs;
o “Qualification and digital certification - A smarter, more efficient mix of sub-scale test, ground test, virtual simulation and flight test will bring faster product innovation cycles within reach.” Abitlity to use FRS technology along the complete development cycle for ground and in-flight measurements will be a stronger enabler to achieve this mission. Faster and more educated design choices will be possible, development and test campaign costs will be reduced and relevant data more rapidly acquired.

Providing a state of the art, modular test bed for non-intrusive measurements

SINATRA will provide a test rig to aero-engine and aircraft manufacturers as well as other academic and research organisations which will offer capabilities to unlock the complex intake aerodynamics which are critical for the safe operation of closely coupled aircraft engine concepts. SINATRA’s methods for complex flow diagnostics and analysis will eventually produce metrics that will educate the engine design process and will accelerate the engine testing and certification phases. This will strongly influence the timescales and costs of novel engine development programmes.

Improving the overall technique to create new markets opportunities for other applications

Unlike most laser-optical measurement methods, the FRS technique is not tailored to a specific application (e.g. reacting flows in spectroscopic methods), but it pursues a universal approach that is suitable for the characterisation of aerodynamic flow processes, multi-phase flows or reacting flows typically found in gas turbine or automotive combustion systems, high pressure turbines or other chemical and process engineering applications where temperature, pressure and velocity data are key requirements.

Improving EU competitiveness and mobility

The mastering of closely-coupled BLI propulsion systems allows the European sector to propose new aircraft concepts within an increasingly electrified world with a variety of new mobility missions (hybrid electric regional or business jet, air taxis, smart rotor craft, etc.) all of which will improve the mobility offering for EU citizens within the 2050 timeframe. This will improve their competitiveness by allowing them to gain the knowledge to propose these aircraft as products sooner than their worldwide competitors.