亚格子模型对泵喷推进器宽带非定常力预测的影响研究

Effects of Subgrid-Scale Models on Broadband Unsteady Force Prediction of Pump-Jet Propulsor

关键词:  泵喷推进器  大涡模拟  宽带非定常力  亚格子模型  非定常流动

Key words:  Pump-jet propulsor  Large eddy simulation  Broadband unsteady force  Subgrid-scale model  Unsteady flow

摘要:

为了研究亚格子模型对泵喷推进器非定常流动与宽带非定常力预报结果的影响，采用分块结构化网格建立了模型尺度下艇后泵喷推进器的计算模型，并进行了大涡模拟数值计算。从艇尾非定常流场特征量和推进器转子脉动载荷两个方面对比了三种不同亚格子模型计算结果的差异，并分析了泵喷内部流动与转子非定常力间的内在联系。研究结果表明：三种亚格子模型均能得到含有叶频宽带峰的轴向推力谱，且整体趋势相近。泵喷转子上游的湍流强度和尺度的分布对亚格子模型较敏感，其中Smargrinsky-Lilly模型得到的湍流强度较强，尺度较大，该模型下的湍流谱在非平衡区量级较大，但由低频向高频的衰减较快，并且预测到的分离区范围大，导叶尾缘脱落涡分散，导致转子上游来流空间分布不均程度较强。对于转子叶片上的载荷脉动，Smargrinsky-Lilly模型预测的推力谱中线谱成分明显，并且叶频处宽带谱峰“陡峭”，而WALE模型和KET模型的结果宽带特性较强，对比非定常推力测试结果可知，WALE模型和KET模型更适于该问题宽带非定常力预测。

Abstract:

In order to study the effects of subgrid-scale model on the prediction result of unsteady flow field and broadband unsteady force， a numerical calculation model of pump-jet propulsor with submarine was established using block-structured grids and large eddy simulation was carried out. The calculated quantity of unsteady flow field at the stern and unsteady loadings on rotor by three different subgrid-scale models were compared. The intrinsic connection between internal flow of pump-jet propulsor and broadband unsteady force was analyzed. The study shows that all the three subgrid-scale models enable the broadband humps at blade passing frequency in unsteady thrust spectra and the overall trends are similar. The distribution of turbulence intensity and scale upstream the rotor is sensitive to subgrid-scale model， among which Smargrinsky-Lilly model predicts stronger turbulence intensity， larger scale， higher spectral magnitude in nonequilibrium region and more rapid decline from low frequency to high than other two models. Meanwhile， Smargrinsky-Lilly model predicts broader separation regions and more scattered vortex shedding from the trailing edge of stator， making the spatial distribution of inflow upstream the rotor more inhomogeneous. The spectrum of unsteady thrust from Smargrinsky-Lilly model has apparent line-spectrum components and ‘steep’ humps at blade passing frequencies. While the spectra calculated from WALE and KET model show more apparent broadband characteristics and these two models are more suitable to predict the broadband unsteady force for this issue， when compared with experimental result of unsteady thrust.