Sensitivity analysis of low-density jets and flames
Sensitivity analysis of low-density jets and flames
复制标题
低密度射流和火焰的灵敏度分析
DOI：
10.17863/cam.14083
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发表时间：
2011
影响因子：
27.7
通讯作者：
Gary J. Chandler
中科院分区：
文献类型：
--
作者：
Gary J. Chandler
这项工作代表了一个更广泛的项目的初步步骤，该项目旨在绘制出燃油喷射器和燃烧室中的敏感区域。采用低马赫数Navier-Stokes方程的直接数值模拟（DNS）方法计算了轴对称低密度射流和升力射流扩散火焰的直接线性和伴随全局模态。伴随的全球模态提供了对开环外部强迫和加热最敏感位置的地图。对于这里考虑的射流，最敏感的区域是在区域的入口。利用一般的结构灵敏度框架，得到了全局模态特征值对力反馈和热阻力的灵敏度。力反馈可以来自流体中的传感器执行器，也可以作为驱动全局不稳定的机制。对于提升的火焰，最敏感的区域位于入口和火焰底部之间。在这个区域，喷流是绝对不稳定的，但火焰的近距离抑制了非反应情况下的全局不稳定。因此，升起的火焰对非反应区的外界干扰特别敏感。将DNS结果与本地分析进行比较。在所有考虑的流动中，最绝对不稳定的区域是在进口处，在进口稍下游的地方有造波器。对于升力火焰，力反馈最敏感的区域靠近造波器的位置，但对于非反应射流，该区域位于造波器的下游和入口附近的绝对不稳定口袋之外。用低马赫数近似分析反应和非反应变密度剪切流的敏感性至今还没有人做过。通过加入反应，在将这些技术应用于实际喷油器方面迈出了一大步。
This work represents the initial steps in a wider project that aims to map out the sensitive areas in fuel injectors and combustion chambers. Direct numerical simulation (DNS) using a Low-Mach-number formulation of the Navier–Stokes equations is used to calculate direct-linear and adjoint global modes for axisymmetric low-density jets and lifted jet diffusion flames. The adjoint global modes provide a map of the most sensitive locations to open-loop external forcing and heating. For the jet flows considered here, the most sensitive region is at the inlet of the domain. The sensitivity of the global-mode eigenvalues to force feedback and to heat and drag from a hot-wire is found using a general structural sensitivity framework. Force feedback can occur from a sensor-actuator in the flow or as a mechanism that drives global instability. For the lifted flames, the most sensitive areas lie between the inlet and flame base. In this region the jet is absolutely unstable, but the close proximity of the flame suppresses the global instability seen in the non-reacting case. The lifted flame is therefore particularly sensitive to outside disturbances in the non-reacting zone. The DNS results are compared to a local analysis. The most absolutely unstable region for all the flows considered is at the inlet, with the wavemaker slightly downstream of the inlet. For lifted flames, the region of largest sensitivity to force feedback is near to the location of the wavemaker, but for the non-reacting jet this region is downstream of the wavemaker and outside of the pocket of absolute instability near the inlet. Analysing the sensitivity of reacting and non-reacting variable-density shear flows using the low-Mach-number approximation has up until now not been done. By including reaction, a large forward step has been taken in applying these techniques to real fuel injectors.