Temporal evolution analysis of in-cylinder flow by means of proper orthogonal decomposition
Temporal evolution analysis of in-cylinder flow by means of proper orthogonal decomposition
复制标题
利用适当正交分解进行缸内流动时间演化分析
DOI：
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
D. Hung
中科院分区：
文献类型：
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作者：
Li Shen;Kwee;Penghui Ge;Fengnian Zhao;D. Hung
内燃机缸内流场及其时间演化对燃烧动力学特性有重要影响。本征正交分解是一种统计工具，通过将这些流场分解为流型（称为本征正交分解模式）和相应的系数，并使其对总体流动能的贡献连续最大化，来分析这些流场。然而，这两个流行的适当的正交分解方法都不能令人满意地描述流场的时间行为。相位相关本征正交分解方法仅限于分析某个发动机相位的空间流场结构。相位不变的正交分解方法试图考虑空间和时间的变化，但在减少统计和物理意义的代价。在这篇文章中，我们试图通过分析低阶相位相关的适当的正交分解模式在多个曲柄角的演变来理解滚流场的时间行为。首先推广相关指数的概念，使两个不同大小的向量字段之间的比较。然后，该度量用于量化在连续曲柄角处获得的两个最低适当正交分解模式之间的方向相似性。观察到的模态形状逐渐和自然地演变在大多数曲轴转角，但在某些曲轴转角在进气过程中显着变化。结果表明，在滚流平面的不同区域，每种低阶模态都具有较强的速度脉动，不同相位下滚流的主要特征需要不同数量的模态来表征。基于这一认识，我们建议使用这些适当的正交分解模式及其系数的部分和，形成缸内滚流的低阶近似模型，以减少流场的复杂性和噪声，同时保留其主要的空间和时间特征。
In-cylinder flow fields and their temporal evolution have strong effect on the combustion dynamics of internal combustion engines. Proper orthogonal decomposition is a statistical tool to analyze these flow fields by decomposing them into flow patterns (known as proper orthogonal decomposition modes) and corresponding coefficients with their contribution to the ensemble flow kinetic energy successively maximized. However, neither of the two prevailing proper orthogonal decomposition approaches satisfactorily describes the temporal behavior of the flow fields. The phase-dependent proper orthogonal decomposition approach is limited to analyzing spatial flow structures at a certain engine phase. The phase-invariant proper orthogonal decomposition approach attempts to account for both spatial and temporal variations, but at the expense of diminished statistical and physical significance. In this article, we seek to understand the temporal behavior of tumble flow fields by analyzing the evolution of low-order phase-dependent proper orthogonal decomposition modes over multiple crank angles. The concept of relevance index is first generalized to enable comparison between two vectorial fields of different sizes. This metric is then used to quantify the directional similarities between the two lowest proper orthogonal decomposition modes obtained at sequential crank angles. The mode shapes are observed to evolve gradually and naturally over most crank angles, but change significantly at certain crank angles during intake. The results indicate that each of the low-order modes features strong velocity fluctuations in different regions of the tumble plane, and different numbers of modes are needed to represent the dominant features of tumble flow at different engine phases. Based on this understanding, we propose to use the partial sum of those proper orthogonal decomposition modes and their coefficients to form a low-order approximation model of the in-cylinder tumble flow, in order to reduce flow field complexity and noise while retaining its major spatial and temporal features.