A numerical strategy for modelling rotating stall in core compressors
A numerical strategy for modelling rotating stall in core compressors
复制标题
核心压缩机旋转失速建模的数值策略
DOI：
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发表时间：
2007
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通讯作者：
M. Vahdati
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作者：
M. Vahdati
本文将重点讨论一个特定的核心-压缩机不稳定性，旋转失速，因为迫切的工业需求，以改善目前的设计方法。旋转失速时叶片响应的确定是一个困难的问题，没有可靠的方法。在旋转失速过程中，叶片遇到失速单元，激励取决于这些单元的数量、大小、确切形状和转速。长期目标是通过避免振动模式和旋转失速模式特征之间的潜在匹配，最大限度地减少旋转失速激励引起的强迫响应。核心压气机旋转失速现象的精确数值模拟需要使用包含数千万个点的网格对大量叶栅进行建模。时间精确的非定常流计算可能需要运行几次发动机旋转，以启动旋转失速，并且在完全发展之前需要更多。旋转失速起始的困难来自于缺乏对航空发动机固有的触发扰动的描述。由于数值模型代表对称组件，旋转失速起始的唯一随机机制由数值舍入误差提供。在这项工作中，旋转失速是通过引入少量的几何失谐的转子叶片。模拟失速附近流动的另一个主要障碍是确定适当的上游和下游边界条件。获得这种流动的可靠边界条件可能非常困难。在本研究中，低压压缩（LPC）域被放置在核心压缩机的上游。用这种方法，只指定远场大气边界条件，这是从飞机的速度和高度。模型中最后一个压气机叶片排后放置的带阻流器的变面积喷嘴用于在下游施加边界条件。这种方法代表了对发动机进行建模。
The paper will focus on one specific core‐compressor instability, rotating stall, because of the pressing industrial need to improve current design methods. The determination of the blade response during rotating stall is a difficult problem for which there is no reliable procedure. During rotating stall, the blades encounter the stall cells and the excitation depends on the number, size, exact shape and rotational speed of these cells. The long‐term aim is to minimize the forced response due to rotating stall excitation by avoiding potential matches between the vibration modes and the rotating stall pattern characteristics. Accurate numerical simulations of core‐compressor rotating stall phenomena require the modelling of a large number of bladerows using grids containing several tens of millions of points. The time‐accurate unsteady‐flow computations may need to be run for several engine revolutions for rotating stall to get initiated and many more before it is fully developed. The difficulty in rotating stall initiation arises from a lack of representation of the triggering disturbances which are inherently present in aeroengines. Since the numerical model represents a symmetric assembly, the only random mechanism for rotating stall initiation is provided by numerical round‐off errors. In this work, rotating stall is initiated by introducing a small amount of geometric mistuning to the rotor blades. Another major obstacle in modelling flows near stall is the specification of appropriate upstream and downstream boundary conditions. Obtaining reliable boundary conditions for such flows can be very difficult. In the present study, the low‐pressure compression (LPC) domain is placed upstream of the core compressor. With such an approach, only far field atmospheric boundary conditions are specified which are obtained from aircraft speed and altitude. A chocked variable‐area nozzle, placed after the last compressor bladerow in the model, is used to impose boundary conditions downstream. Such an approach is representative of modelling an engine.