不同直径圆球诱导燃烧的振荡机制与频率特性

Oscillation Mechanism and Frequency Characteristics of Combustion Induced by Spheres with Different Diameters

关键词:  激波诱导燃烧  振荡燃烧  频率特性  高速圆球  基元反应

Key words:  Shock-induced combustion  Oscillating combustion  Frequency characteristics  High-speed sphere  Detailed combustion mechanism

摘要:

为了分析不同直径圆球诱导振荡燃烧的规律，并揭示圆球大小在振荡燃烧现象中所发挥的深层次作用，采用二维轴对称Euler方程和基元反应模型，对不同直径的圆球在H₂/air预混气体中诱导振荡燃烧的现象开展数值模拟研究。研究发现，振荡频率并不是简单地随直径增大而逐渐从高频向低频连续过渡，而是存在两次突变，形成了超高频、高频以及低频三种振荡燃烧模态。在两种模态间过渡时，振荡达到稳定状态前，会存在一段双频耦合的振荡阶段。三种不同振荡燃烧模态的产生是受到了不同振荡机制的作用，而两种模态间过渡时的双频耦合现象则是两种机制相互竞争的结果。

Abstract:

In order to analyze the law of oscillating combustion induced by spheres with different diameters and to reveal the inherent effect of sphere size on the oscillation phenomenon， numerical simulations are carried out to investigate the oscillating combustion phenomenon in a H₂/air premixed gas mixture induced by spheres with different diameters， by solving the two-dimensional axisymmetric Euler equations along with a detailed combustion mechanism. Results show that as the sphere diameter increases， the frequency of oscillating combustion does not decrease continuously， but with two abrupt drops， which implies that there exist three modes in the high-speed sphere-induced oscillating combustion phenomenon， namely the superhigh-frequency mode， the high-frequency mode， and the low-frequency mode. During the transition of two modes， there exists a metastable oscillating state of double-frequency coupling before the oscillation reaches its stable state. Moreover， the appearance of these three different modes is affected by different oscillation mechanisms， and the double-frequency coupling phenomenon during the transition of two modes is resulted from the competition of two mechanisms.