报告简介：

One of the most important steps in the prediction of thermoacoustic oscillations is the determination of the acoustic response of the flame as an element in an acoustic network, in the form of a flame describing function. To measure this, researchers often have to confine the flame in a system with its own acoustic response. Separating the pure flame response from that of the system can be complicated by the nonlinear effects that the flame has on the overall system response. In this talk, we will investigate whether it is possible to obtain a flame response via the usual methods of dynamic chemiluminescence and pressure measurements, starting from an unforced system with incipient self-excited oscillations at a given natural frequency, in the form of a stabilized flame at atmospheric pressure confined by a 700 mm tube acting as a combustor. The flame is forced at discrete frequencies from 20 to 400 Hz, away from the self-excited mode, and its response is measured with OH* chemiluminescence. This response is then compared to that of a flame in a short tube with no other excitation. The results show that both the gain and phase can be entirely dominated by the behavior of the self-excitation, such that in general it is not possible to extract reliable gain and phase information as if the forced and self-excited modes acted independently and linearly. Although the gain in this particular case was not significantly affected, the phase information of the original flame became dominated by the triggered self-excited mode. Boundary conditions and systems used for flame acoustic forcing therefore need to be carefully controlled whenever there is a possibility of self-excitation.

报告人简介：

Dr Larry Li received his BASc and MASc in Mechanical Engineering from the University of British Columbia (Canada) as a Natural Sciences & Engineering Research Council Scholar in the Applied Fluid Mechanics Laboratory. He then went on to study for a PhD at the University of Cambridge (UK) as a Bill & Melinda Gates Scholar in the Injector Dynamics Group. After graduating, he stayed on at Cambridge as a Research Associate before joining HKUST in 2014 as an Assistant Professor in the Department of Mechanical & Aerospace Engineering. Dr Li’s research focuses on flow instability, combustion, thermoacoustics, nonlinear dynamics and multiphase flows, with applications ranging from aircraft propulsion to spray painting.

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