Tiziano Pagliaroli

Optical Investigation of Thermo-Acoustic Instabilities in Turbulent Flames

Nowadays, analysis of both fluid-dynamic and thermo-acoustic instabilities is of industrial interest; new strategies and instruments to capture and foresee the onset of instabilities are strategic for active control of combustion. In fact, this is a major concern for future combustors, as they will tend to employ some form of premixing to reduce NOx .I n this paper investigation of thermo-acoustic instabilities is mainly carried out by means of photo-diodes with some support of pressure transducers. The analysis is performed over three burners, premixed and nonpremixed, fed with different fuels and with power ranging from 250kW to 500kW. Spectra and correlations of radiant energy are examined. Results show that radiant energy signal is sufficient to characterize the operating mode of a burner, stable or unstable, and in particular, it can be used for early detection of thermo-acoustic instabilities.

Acoustic and Aeroacoustic Characterization of Rectangular Partial Enclosures

Pressure fluctuations generated by turbulent jets into rectangular partial enclosures (RPEs) are studied experimentally over a broad range of geometrical and flow parameters. PIV measurements are carried out to characterize the overall aerodynamics and wall pressure measurements are conducted with an array of microphones flush mounted at the walls of the cavity. In order to interpret the pressure measurements, the acoustic properties of the geometry are investigated both experimentally, through a modal test analysis, and numerically with a standard FEM approach. Particular emphasis is put on the first dominant mode that affects significantly the aeroacoustic measurements and whose frequency is shown to scale as that of a Helmholtz resonator.