CONTROL OF COMBUSTION AND ACOUSTICALLY COUPLED FLUID DYNAMIC INSTABILITIES.

摘要

The purpose of the present research is to demonstrate experimentally a set of methods for the active control of combustion and acoustically coupled fluid dynamic instabilities. These methods are based on the theoretical understanding of the interaction of mass, momentum or energy sources with a disturbance in the system. The disturbance could be nonlinear and either vortical, acoustic or in the entropy mode. It has been shown that periodic addition of mass, momentum or energy can result in either the amplification or the decay of the energy in a periodic disturbance depending on the phase in which this addition occurs. Successful control has been achieved in several cases of fluid dynamic and combustion instability ranging from laboratory scale experiments to an operational, large combustion tunnel.;The method of heat addition was used to successfully control oscillations in a Rijke tube, a whistler nozzle, resonance in a pipe set up by a loudspeaker, and a turbulent pipe flow with superimposed acoustic resonance. It was found that more control heat is necessary to suppress oscillations with a large background turbulent noise. Drag forces generated by fine screens was used to suppress the oscillations in a whistler nozzle. A feedback mechanism was designed to oscillate the screens in the proper phase to achieve the desired control action. The resonance in a pipe set up by a loudspeaker was suppressed by periodic mass addition using a feedback control system. Finally, a combination of screens and heating coils was used to control oscillations in a large combustion tunnel. The methods of control explored in this work are independent of the source of instability, and hence have a broad range of applications in real systems.