1,721,051 research outputs found
Modeling of Combustor Non-Uniformities Evolution Through a High-Pressure Turbine Stage
No full textIn modern gas turbines, the reduction of pollutant emissions can be achieved by employing lean-burn combustors. At the combustion chamber outlet, the flow is non-uniform and characterized by a residual swirl superimposed to steady (hot streak) and unsteady (entropy waves) temperature disturbances. During the transport from the combustor outlet to the turbine inlet, these disturbances are weakly dissipated and persist at the turbine inlet. Therefore, the interaction between the combustor non-uniformities and the turbine has to be deeply studied. To study combustor-turbine interaction experimentally, a common practice is to install combustor simulators on non-reactive turbine test facilities. For this purpose, a combustor simulator was designed and installed at the Politecnico di Milano turbine test facility. This device can generate a combined steady/unsteady temperature disturbance and swirl profile at the turbine inlet. Using this layout, several experimental campaigns have been carried out changing the type of injected disturbance, the injection position, and the turbine operating condition. In this paper, the data collected from these experiments have been used to develop simplified models to predict the transport and dissipation of combustor perturbations through a turbine's first stage. In the open literature, few attempts are discussed regarding the modeling of combustor-turbine interaction that-in authors' opinion-represents an important tool for preliminary turbine design
THE ROLE OF TURBINE OPERATING CONDITIONS ON COMBUSTOR-TURBINE INTERACTION - PART 2: LOADING EFFECTS
No full textTHE ROLE OF TURBINE OPERATING CONDITIONS ON COMBUSTOR-TURBINE INTERACTION - PART 1: CHANGE IN EXPANSION RATIO
No full textImpact of swirling entropy waves on a high pressure turbine
No full textThe harsh environment exiting modern gas turbine combustion chamber is characterized by vorticity and temperature perturbations, the latter commonly referred as entropy waves. The interaction of these unsteadiness with the first turbine stage causes non-negligible effects on the aerodynamic performance, blade cooling and noise production. The first of these drawbacks is addressed in this paper by means of an experimental campaign: entropy waves and swirl profile are injected upstream of an axial turbine stage through a novel combustor simulator. Two injection positions and different inlet conditions are considered. Steady and unsteady experimental measurements are carried out through the stage to address the combustor-turbine interaction characterizing the injected disturbance, the nozzle and rotor outlet aerothermal field. The experimental outcomes show a severe reduction of the temperature perturbation already at stator outlet. The generated swirl profile influences significantly the aerodynamic, as it interacts with the stator and rotor secondary flows and wakes. Furthermore, the clocking position changes the region most affected by the disturbance, showing a potential modifying the injection position to minimize the entropy wave and swirl profile impact on the stage. Finally, this work shows that in order to proficiently study entropy waves, the unsteady aerodynamic flow field stator downstream has to be addressed
The Role of Turbine Operating Conditions on Combustor-Turbine Interaction - Part I: Change in Expansion Ratio
No full textAeroengine lean-burn combustors release vorticity and temperature perturbations that, interacting with the first turbine stage, impact the stage aerodynamics, the blade cooling, and noise production. The first of these issues is addressed in this paper that is Part I 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
Transport of swirling entropy waves through an axial turbine stator
Full text linkThe transport of entropy waves and their impact on the stage aerodynamics are still open questions. This paper shows the results of an experimental campaign that focuses on the swirling entropy waves advection through an axial turbine stator. The research aims at quantifying the aerodynamic impact of the swirling entropy waves on the first nozzle and characterizing their transport. The disturbance is generated by a novel entropy wave generator that ensures a wide set of different injection parameters. The device injects the disturbance axially, four different clocking positions are investigated. Measurements show a severe temperature attenuation of the swirling entropy wave at stator outlet. The high temperature location changes with the injection position as a result of the different interaction with the stator secondary flows. Depending on the injection position, the aerodynamic flow field is strongly perturbed by the injected swirl profile, instead the entropy wave effect is negligible
The Role of Turbine Operating Conditions on Combustor-Turbine Interaction-Part II: Loading Effects
No full textAero-engine combustors burn a lean and premixed blend releasing vorticity and temperature perturbations. Interacting with the first turbine stage, these disturbances impact the cascade aerodynamics, add criticality to the blade cooling, and are sources of noise. The first of these issues is addressed in this paper, focusing on off-design turbine conditions, as experienced by aero-engines in their duty. This paper, Part II of a two-fold contribution, analyses the effect of the stage loading obtained by changing the rpm (three different values) at the same expansion ratio of 1.4, representative of subsonic flow conditions. Engine-representative disturbances are generated by a combustor simulator able to produce a swirling entropy wave. Two injection positions and four injection patterns are considered. Experimental measurements are carried out through the stage, measuring the injected disturbance and the aerothermal flow field downstream of the stator and the rotor. Results show that the swirl profile mostly impacts the stage aerodynamics. The different work extraction and the interaction with secondary flow structures change the entropy wave transport, diffusion, and decay through the rotor. Furthermore, the increased angle of the incidence caused by the injected disturbance can make the blade stall under the most loaded operating condition
TURBULENCE MEASUREMENTS DOWNSTREAM OF A COMBUSTOR SIMULATOR DESIGNED FOR STUDIES ON THE COMBUSTOR-TURBINE INTERACTION
Full text linkTurbulence Measurements Downstream of a Combustor Simulator Designed for Studies on the Combustor–Turbine Interaction †
Full text linkTurbulence intensity impacts the performance of turbine stages and it is an important inlet boundary condition for CFD computations; the knowledge of its value at the turbine inlet is then of paramount importance. In combustor–turbine interaction experimental studies, combustor simulators replace real combustors and allow for the introduction of flow perturbation at the turbine inlet. Therefore, the turbulence intensity of a combustor simulator used in a wide experimental campaign at Politecnico di Milano is characterized using a hot-wire probe in a blow-down wind tunnel, and the results are compared to URANS CFD computations. This combustor simulator can generate a combination of a swirl profile with a steady/unsteady temperature disturbance. In the cold unsteady disturbance case, hot-wire measurements are phase-averaged at the frequency of the injected perturbation. The combustor simulator turbulence intensity is measured at two different axial positions to understand its evolution
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