时       间：2017年9月12日  上午10：00
地       点：新教二楼117

主  讲  人：赵丹  副教授
主 办 单 位：化学系
主讲人简介：赵丹，英国剑桥大学机械与航天工程专业博士，现任教于新西兰坎特伯雷大学机械系。作为第一作者和通讯作者已发表SCI论文60余篇，总引用达1300多次，累计H-INDEX 22分。同时在SCI期刊<Aerospace Science and Technology>,<Journal of Low Frequency Noise>, <Vibration and Active Control>任副主编; <Progress in Aerospace Sciences >任编委。曾在华盛顿第46届美国航空航天、流体力学大会上担任分会主席。
内 容 简介：Self-sustained combustion oscillations (also known as combustion instability) most often arise due to the coupling between unsteady heat release and acoustic waves. The large-amplitude oscillations are wanted in thermoacoustic engine systems. However, they are undesirable in many other systems such as aero-engine afterburners, rocket motors, ramjets and gas turbines, since the oscillations may become so intense that they cause structural damage and costly mission failure. Combustion system is typically associated with non-orthogonal eigenmodes and flow disturbances can undergo transient growth to trigger combustion instability.  In this work, a Rijke-type combustion system with a laminar premixed flame confined is considered to investigate its non-normality and the resulting transient growth. Unsteady heat release from the flame is assumed to be caused by its surface variations, which results from the fluctuations of the oncoming flow velocity. Coupling the flame model with a Galerkin series expansion of the acoustic waves present enables the time evolution of flow disturbances to be calculated, thus providing a platform on which to gain insights on the Rijke–type system stability behaviors. Both eigenmodes orthogonality analysis and transient growth analysis of flow disturbances are performed. In order to achieve strict dissipativity (i.e., unity maximum transient growth), a transient growth controller is systematically designed and tested in both systems. Comparison is then made between the performance of the LQR (linear-quadratic regulator) controller and that of the transient growth controller. It is found in both systems that the transient growth controller achieves both exponential decay of the flow disturbance energy and unity maximum transient growth.