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2017年4月13日 The effect of self-excited thermoacoustic oscillations on measurements of the flame describing function

发布时间:2017-4-7 12:17:14  点击次数:260

主  办:力学系与湍流重点实验室
报告人:Prof.Larry Li
时  间:2017年4月13日 周四 14:00—15:00
地  点:工学院1号楼210室
主持人:杨越 特聘研究员


报告内容简介:


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:


                                               
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