The thermo-acoustic instability in the combustion process of a gas turbine is caused by the interaction of the heat release mechanism and the pressure perturbation. These acoustic vibrations cause fatigue failure of the combustor and decrease the combustion efficiency. This study aims to develop a segmented dynamic thermo-acoustic model to understand combustion instability of a gas turbine. Then, the combustion instability was designed using the acoustic heat release model, and the designed instability model was segmented using the finite difference method, to evaluate the characteristics of flame propagation at each node. The combustion instability model was validated using experimental data to verify the instability amplitude. Also, the optimal node number was determined using the adiabatic flame temperature response. 10 nodes were selected in this study. A sensitivity analysis showed the predicted instability amplitude decreased when the nodes increased until node 4, due to heat generation. However, above 4 nodes the amplitude decreased, since the combustion outlet was directly connected to the ambient. As a result, the segmented combustion instability model was able to evaluate the flame propagation characteristics more accurately and found the largest area of instability was near the flame area.

This study describes an experiment that validates scaling rules for the design of thermal mass, coupled with buoyancy ventilation, suggesting that wood can perform as well as concrete if these rules are respected. The scaling rules potentially offer a shortcut for early design, showing how to tune the interior temperature and rate of buoyancy ventilation by adjusting the thickness and surface area of an internal thermal mass. A pair of test chambers (H~1m), comparing wood and concrete internal thermal masses, were located in Alabama, USA and Montreal, Canada, and left outside in sun- and-wind-sheltered environments for consecutive months. The thermal mass thicknesses were optimized so the chambers would maintain similar interior temperatures and airflow rates. The scaling rules predicted the behavior of the chambers with reasonable accuracy and both the concrete and wood thermal masses performed equivalently. For instance, the test chambers in Alabama were both designed to damp the maximum exterior temperature by a factor 1-1/Ai ≈ 0.7 and produce a maximum ventilation flow rate of Q ≈ 0.37 l/s. The measured damping was 1-1/Ai = 0.81±0.1 and 1-1/Ai = 0.81±0.13 for the concrete and wood chambers, respectively, while the maximum flow rates were 0.374±0.03 and 0.36±0.04 l/s, respectively.

No abstract