Numerical investigation on combustion instabilities and its passive control.
Date of Issue2012
School of Mechanical and Aerospace Engineering
Combustion instabilities are caused by the interaction between unsteady heat releases and acoustic waves. Under certain conditions, the mutual interaction can grow to large oscillations damaging to structures. A lab-scale setup to demonstrate and investigate the combustion instabilities is Rijke tube which is a straight tube with heat source placed inside the tube. To gain insight of the generation mechanism of combustion instabilities, numerical simulation of combustion in a Rijke like tube is carried out in the present study. Different from the conventional Rijke tube, a new designed Rijke-Zhao tube, which has a mother tube (bottom stem) splitting into two or more bifurcating daughter tubes (i.e. upper branches) with different lengths, is considered. As a premixed laminar flame is placed inside the mother tube, it provides a mechanism to produce self-excited combustion oscillations (also known as combustion instabilities). To compare with our experimental results, 2D numerical simulation of the Rijke-Zhao tube by using ANYSYS Fluent 13.0 is conducted. It was found that numerical model can capture the flow field and acoustic characteristics, predicting limit-cycle and its frequencies of the thermoacoustic oscillations very well. Moreover, the mode shape predicted by the simulation shows that the mode frequency is affected by the treatment on the boundary end. Two configurations are simulated: one case is considered as all acoustically open ends and another is considered as two acoustically closed and one acoustically open end. The effect of different treatment on the boundary end is presented.