基于多重条件矩封闭模型的反应羽流大涡模拟

Doubly-Conditional Moment Closure for Large Eddy Simulation of a Reactive Plume

针对中等Reynolds数下的浮力反应羽流进行大涡模拟.采用混合分数和标量耗散率双条件矩封闭方法模化过滤反应源项,与直接数值模拟数据的对比表明,耦合双条件矩封闭模型的大涡模拟具有很好的计算精度和可靠性.模拟结果表明,浮力控制了反应羽流的外侧大尺度涡旋运动,该区域较大的标量耗散率导致最高温度区域不在火焰前锋面位置.反应羽流中存在绝对不稳定、浮力和射流不稳定模式,而浮力模式和变密度下的绝对不稳定控制着反应羽流的动力学进程.此外,建表内插的方法可大大节约计算资源,是实际工程计算中值得推荐的方法.

Large eddy simulation （LES） and direct numerical simulation （DNS） of two-dimensional reactive plumes for moderate Reynolds number are conducted to assess the performance of subgrid-scale LES models in transitional and turbulent reactive flows. The LES is conducted by the ＂conditional moment closure＂ （CMC） method developed by Bilger and Klimenko, and the scalar dissipation rate is introduced as a second conditioning variable into the first-moment, singly conditional moment closure model to describe extinction and reignition effects. The LES results are appraised by detailed comparison with DNS data. It is found that the asymmetrical deformation mode associated with combustion-induced buoyancy is enhanced and its maximum value can exceeds that of the symmetrical deformation mode （ the jet preferred mode of instability）. Furthermore, the reactive plume undergoes self-sustained oscillations （global mode） at a well-defined frequency with a corresponding Strouhal number close to zero.