基于DDES方法的叶栅分离旋涡的非定常流动数值研究

Unsteady Numerical Investigation on Cascade Separation Vortex Flow Based on Delayed Detached-Eddy Simulation

关键词:  延迟分离涡方法  旋涡运动  脱落频率  非定常模拟

Key words:  Delayed detached-eddy simulation  Vortex motion  Shedding frequency  Unsteady simulation

摘要:

为了研究叶栅分离旋涡的非定常流动特性，选取亚声速叶栅为研究对象，进行了基于延迟分离涡模拟方法(DDES)的非定常数值模拟。针对进口Ma0.3的情况，对比分析了进口攻角、叶栅稠度、叶片弯角、叶片中弧线弯度分布和叶片厚度等因素对于叶栅分离旋涡运动的影响。结果表明，当攻角增大时，尾迹附近流场会逐渐由定常模式转化为非定常对涡脱落模式，同时对涡脱落频率不断减小；随着攻角的进一步增大，叶背分离强度不断增加，叶背分离涡开始单独脱落，并主导流场旋涡运动。强烈的叶背分离涡脱落引起了叶片气动力的剧烈脉动，其幅值是小攻角状态下由尾迹对涡脱落引起叶片气动力脉动的30倍以上。叶栅几何参数的改变对于流场旋涡运动同样有很大影响，流场同样呈现出“定常尾迹”、“对涡脱落”、“叶背分离涡脱落”这三种主要的旋涡运动形式之一。叶背分离点的相对位置则是影响旋涡非定常运动形式和旋涡脱落频率的主要内在因素。

Abstract:

In order to investigate the unsteady characters of cascade separation vortex flow，the unsteady numerical simulations based on Delayed Detached-eddy Simulation(DDES) were carried out to study the flow fields of a certain subsonic cascade. The effects of many factors，including angle of attack，cascade solidity，profile turning，camber line curvature distribution and profile thickness，on the motion of cascade separation vortex were analyzed when the inlet Ma equals 0.3. The results show that with an increasing angle of attack，the flow field near trailing edge gradually transforms to unsteady vortex-pair shedding from steady flow，and meanwhile，the frequency of vortex decreases. With a further increase of angle of attack，the suction side separation vortex becomes stronger and sheds solely to dominant vortex field. The strong shedding of suction side separation vortex leads to the drastic fluctuation of blade force. And the fluctuation amplitude is over 30 times higher than that caused by shedding vortex-pair near trailing edge in small angle of attack conditions. In addition，the geometry parameters also have great influences on vortex field of cascade. In each case，flow field shows one of three vortex motion patterns which are “steady wake”，“shedding vortex-pair” and “shedding suction side separation vortex”. The fundamental factor to affect the vortex motion pattern and shedding frequency is the relative position of separation point on suction side.