Abstract
Modern aero-engine combustion chambers burn a lean and premixed mixture, generating a turbulent flame which involves large heat-release fluctuations, thus producing unsteady temperature phenomena commonly referred to as entropy waves (EWs). Furthermore, to enhance the fuel air mixing, combustion air is swirled, leading to vorticity disturbances. These instabilities represent one of the biggest challenges in gas turbine design. In this paper, the design and testing of a novel entropy wave generator (EWG) equipped with a swirler generator (SG) are described. The novel EWG will be used in future works on the high-speed test rig at Politecnico di Milano to study the combustor–turbine interaction. The paper shows the process of the EWG geometry and layout. The EWG is able to produce an engine-representative EW, the extreme condition is at the maximum frequency of 110 Hz, a peak-to-valley temperature value of 20 °C and swirling angles of ±25° are measured. By virtue of these results, the proposed system outperforms other EWG devices documented in the literature. Furthermore, the addition of a swirling generator makes this device one of a kind.
Highlights
In order to match the strict regulations on pollutant emissions, modern aero-engines feature a lean premixed combustion to limit combustion temperature, and NOx production
The combination of the swirl motion and entropy wave makes the design of the first turbine stages challenging: this unsteadiness complicates the aerodynamics, they have a role in the definition of the stage performance [1,2]; they are responsible for the production of entropy noise [3,4,5,6] and have an effect on the heat transfer [7,8], which implies modification in the blade cooling system
Sattelmayer [9] states that entropy waves are diffused by the flow turbulence, whereas in [10], the authors demonstrate that entropy wave dispersion from combustor to turbine is weak and the entropy wave strength is preserved at the combustor exit
Summary
In order to match the strict regulations on pollutant emissions, modern aero-engines feature a lean premixed combustion to limit combustion temperature, and NOx production This type of combustion involves a complex evolution of the front flame that results in a strong heat release unsteadiness. The combination of the swirl motion and entropy wave makes the design of the first turbine stages challenging: this unsteadiness complicates the aerodynamics, they have a role in the definition of the stage performance [1,2]; they are responsible for the production of entropy noise [3,4,5,6] and have an effect on the heat transfer [7,8], which implies modification in the blade cooling system All these phenomena acknowledge that combustor instabilities still exist at the turbine inlet. Semlitsch et al [11] have demonstrated by means of a computational study that swirl persists at the combustor exit
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