Cooled Fast-Response Wall Pressure Taps for Combustion Chamber Measurements

Project Information

FAST TAPS

Grant agreement ID: 820946

DOI

10.3030/820946

Project closed

EC signature date 4 October 2018

Start date 5 November 2018

End date 4 August 2022

Funded under

• SOCIETAL CHALLENGES - Smart, Green And Integrated Transport

Total cost

€ 297 566,25

EU contribution

€ 297 533,25

Coordinated by

VON KARMAN INSTITUTE FOR FLUID DYNAMICS
Belgium

Periodic Reporting for period 5 - FAST TAPS (Cooled Fast-Response Wall Pressure Taps for Combustion Chamber Measurements)

Reporting period: 2021-05-05 to 2022-08-04

Summary of the context and overall objectives of the project

Environmental aspects have been historically the main driver for step changes in the gas-turbine technology. This is the case of pollutant (and noise) emissions which triggered, since the late 80s, a vivid research activity on the development of low NOx (and low noise) combustion chambers. The basic philosophy of low-NOx burner consists in controlling the flame temperature to inhibit the NOx formation at high-temperature, a result that can be obtained by adopting a lean fuel-to-air mixture. However, despite their extremely advanced design, low-NOx burners are plagued by reliability issues due to severe combustion instabilities which, once amplified by the high-pressure turbine stage and by acoustic coupling with the combustor, lead to a severe heat release on the burner walls and to undesirable high amplitude structural vibrations. Consequently, improved low-NOx technologies are one of the key strategies to meet the challenging targets set by the Strategic Research and Innovation Agenda for 2035 and beyond. Nevertheless, a further maturation is required for the lean combustion approach that implies an even better emission performance, a reduced noise footprint, a wider operational flexibility, and an improved reliability. In this view, a more detailed knowledge is required on the formation mechanism of combustion instabilities and of their dynamics, leading to the need of more advanced and more performant measurement techniques that could support an experimental assessment of the phenomena at engine conditions.
In the framework of the FAST TAPS project, the main objective was the design, manufacturing, and qualification of 8 reliable fast-response large bandwidth wall-static pressure taps for combustion chamber measurements. To achieve this objective, a design methodology had to be developed in order to maximize the frequency bandwidth while still safeguarding the sensor integrity, to protect the fragile sensing element against the harsh combustor environment while still minimizing the probe intrusiveness, and finally, to guarantee a reliable probe performance. Furthermore, an extensive validation and qualification procedure for the prototype and final production probes had to be developed as well.
The FAST TAPS project achievement resulted in the design, manufacturing and full qualification of 8 probes, along with the delivery of a dedicated external cooling system allowing the simultaneous use of 6 probes in the combustor of a ground-based turboshaft gas turbine test rig. The availability of this type of instrumentation would be a fundamental tool to extend the knowledge around combustion instabilities, while directly supporting the development of more performant combustion control systems.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first stage of the project was fully dedicated to designing a probe that would allow the measurement of time-resolved wall-static pressure data in a harsh combustor environment. To meet this requirement, a screened-recessed sensor layout circumferentially surrounded by counter-flow cooling channels and using a commercial off-the-shelf Kulite sensor was adopted. The usable frequency bandwidth, limited by the acoustic resonance introduced by the screened-recessed sensor layout, was theoretically predicted at 45 kHz using empirical correlations, and was further experimentally measured to be 50 kHz by means of dedicated shock tube tests. The water-based cooling layout was assessed by means of a quasi-2D conjugate heat transfer model, and state-of-the-art 3D RANS conjugate heat transfer simulations allowed a more detailed assessment of the performance of the cooling layout. The survivability of the sensing element in the harsh combustion chamber environment was demonstrated, with sensor temperatures remaining below 410 K for all investigated coolant flow rates. Finally, the physical environment in which the probe would be integrated allowed to consolidate the probe structural and mechanical design, yielding a probe geometry that enabled its straightforward integration onto the engine casing.
Following a critical review of the proposed probe design, a probe prototype was then produced which was subsequently thoroughly evaluated during the second stage of the project. The structural and mechanical integrity of the prototype was controlled by checking the leakproofness at high internal pressure as well as the pressure losses through the probe with respect to the coolant flow rate. The prototype was then successfully installed in the primary zone of the Safran Tech BEARCAT turboshaft test rig, using Safran Tech's own cooling system as coolant supply source. The probe survived more than 30 minutes at idle engine conditions (where temperature levels in the primary zone already reach beyond 1000 °C), producing valuable and insightful data regarding combustion noise and instabilities. However, a weakness in the sensor packaging meant that soot deposit on the sensor led to a critical sensor failure. As soon as a solution regarding the sensor packaging was adopted, the mass production of 8 probes was successfully achieved during the final stage of the project. The external cooling system, able to provide up to 5 l/min of coolant to 6 probes each simultaneously, was also successfully delivered.
Over the course of the project, the obtained results were actively disseminated by presenting the project outcomes at a Clean Sky 2 workshop on advanced combustor technologies, at 2 symposia on measuring techniques in turbomachinery, as well as at the ASME Turbo Expo 2020 conference. The audience reached through these dissemination activities was mainly academic and industrial in nature. Finally, the exploitation of the knowledge generated within FAST TAPS was also capitalized by means of periodic technical meetings with Safran Helicopter Engines (the Topic Manager), as well as by sharing and discussing comprehensive technical notes and deliverables with the latter.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The Work Package 3 of the Clean Sky 2 Engines ITD can be considered as a direct reaction to the hegemony of the US engine manufacturers in the turboprop market. In the 1800-2000 shp class, the market share of North American actors reaches 83%, a figure that can be reduced only by providing as efficient and cost-effective solutions as possible.
At first instance, the FAST TAPS project modestly but directly contributed to the achievement of the targets set by the Clean Sky 2 Joint Undertaking program by providing 8 fast-response wall-static pressure probes, allowing a deeper understanding of the combustion instability dynamics and combustion noise generation mechanisms in real engine conditions. Such enhanced knowledge could then be employed in the design of advanced combustion chambers with a significantly reduced NOx production and noise footprint.
In second instance, FAST TAPS paved the way towards the development of air-cooled fast-response pressure probes. The availability of such type of tools would enable in the future (going beyond 2020) their implementation in production engines, providing therefore faster and more precise combustion monitoring capabilities as well as more performant combustion instabilities control strategies. Moreover, the availability of such technology could be considered a business on its own and could contribute to the strengthening of the European competitiveness both on the sensors packaging and monitoring-control markets, sectors still dominated by extra-European actors.

FAST TAPS design (top left) ; Integration on BEARCAT (bottom) ; Validation test results (top right)