The Role of Turbine Operating Conditions on Combustor–Turbine Interaction—Part I: Change in Expansion Ratio

Abstract

Aeroengine lean-burn combustors release vorticity and temperature perturbations that, interacting with the first turbine stage, impact the stage aerodynamics, blade cooling and noise production. The first of these issues is addressed in this paper that is part 1 of a two-fold contribution. A detailed experimental analysis is carried out to study the impact on the combustor-turbine interaction of the off-design conditions experienced by aero-engines in their duty. Engine-representative disturbances are generated by a combustor simulator able to produce swirling entropy waves. Two injection positions and four injection cases are studied. Experimental measurements are carried out at three traverses: upstream of the stator, at the interstage, and downstream of the rotor. This paper analyses the effect of the stage expansion ratio: two values are studied, namely 1.4 and 1.76, representative of subsonic and transonic flow conditions. They are chosen imposing similar velocity triangles at the rotor inlet. Results show that the swirl profile considerably impacts the stage aerodynamics. The aerothermal flow field downstream of the stator is modified significantly by the combustor disturbances. Conversely, downstream of the rotor, the differences in aerodynamics lessen. However, the entropy wave persists at the stage outlet and its transport depends on both the operating point and the injection position.

Unsteady Flows and Component Interaction in Turbomachinery

“…However, entropy noise is not strictly associated with the aerodynamic and heat transfer problems discussed in the present paper and is not going to be detailed here. For those who are interested in studying this challenging topic, the works by Gaetani and Persico [58], Gaetani et al [59], Pinelli et al [60], Notaristefano and Gaetani [61,62,63], and Pinelli et al [64] are suggested.…”

Turbulence measurements downstream of a combustor simulator designed for studies on the combustor-turbine interaction

“…At the outlet of the injector, a swirl generator is placed that acts on both the mainstream air and the steady/unsteady generated disturbances. Further details of the combustor simulator are described in Notaristefano and Gaetani (2020).…”

“…In this context, many combustor simulators (used by Andreini et al (2016), Werschnik et al (2017), Notaristefano and Gaetani (2020) and Adams et al (2021)) were conceived to mimic, by nonreactive devices, the combustor released flow and to allow the experimental testing and numerical simulation.…”

“…Several experimental campaigns have been performed at Politecnico di Milano since 2015 (Gaetani and Persico, 2019), focused on the transport of entropy waves within a HP turbine stage. The most recent combustor simulator used to generate the turbineinlet non-uniformities was conceived to combine a swirl profile and entropy waves (Notaristefano and Gaetani (2020)): such an inlet flow field makes this experimental campaign one of a kind. The results of this wide experimental campaign are described in Notaristefano and Gaetani (2023a), Notaristefano and Gaetani (2023b) and Pinelli et al (2023), the interested reader is invited to refer to them for detailed results.…”

“…In Folk and Miller (2019), Cresci et al (2015), and Bacci et al (2015) the turbulence intensity generated by combustor simulators is studied. This paper aims at describing the turbulence field released by the combustor simulator described in Notaristefano and Gaetani (2020) and its decay as the stream propagates downstream. Experiments were performed at different injection conditions and at different distances from the injector.…”