|Ph.D Thesis||Department of Aerospace Engineering|
|Supervisor:||Prof. Levy Yeshayahou|
The performance requirements of any combustion system include maintaining a stable combustion over the entire operating range of fuel/air rates. In some instances, the operating range of the combustor is limited by large pressure oscillations and energy release fluctuations. Although considerable effort has been invested in understanding and controlling this undesirable phenomenon over the last 60 years, it continues to present significant challenges in reliable engine design.
The physical mechanisms involved in the spray combustion instability and its suppression is investigated. Special emphasis was given to diagnostic techniques for analysis of the details of the oscillating streams and their interaction. An advanced method, with highly improved resolution and dynamic range FIV (Fluid Image Velocimetry) was specifically developed for this purpose and applied for velocity field analysis coupled with local measurements of time dependent pressure, temperature, CH*- emission and velocity.
The interaction between two oscillating streams as related to the suppression of the combustion instability was also investigated. The ability of the tested configurations to suppress the combustion instability was demonstrated experimentally.
The significance of the present study is in its focus on the analysis of smart atomizers, which utilize the pressure & velocity oscillations in the combustor for spray modulation. These atomizers will significantly reduce the number of tests required today in a full-scale combustor for the prevention of the longitudinal combustion instability. An additional progress in understanding the fluid dynamic mechanisms related to the interaction between the acoustic oscillations and the vortex structures was achieved.