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.