Influence of riblet structure on loss and stall of cascade at low Reynolds numbers
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摘要:
为了拓宽叶栅在低雷诺数效应影响下有效攻角范围，实现叶栅扩稳、减损的目的，对某小折转角的扩压叶栅开展数值和试验研究。通过研究原型叶栅失速后的湍流主要特征，选择3种角度的表面脊微结构针对其加以控制，研究结果表明：扩散型表面脊是扩大叶栅有效攻角和减小损失的有效手段，特点是扩大正失速边界而不牺牲设计攻角损失，最大减损17.7%；无偏角脊结构可实现大攻角减损，其最大减损19.58%。总的来说，扩散型脊减损效果好于无偏角型，好于汇聚型。另外发现减损后尾迹宽度和损失峰值减小且尾迹扩散中心线推向压力面一侧偏移。
Abstract:To broaden the effective attack angle range of the blade cascade under the influence of low Reynolds number and achieve the purpose of blade cascade expansion and loss reduction, numerical and experimental researches on a small deflection angle diffuser blade cascade were conducted. Three riblet-structures with different angles were selected to control it by studying the main characteristics of turbulence after blade stall. The research results indicated that diffusion type surface ridges are an effective means to expand the effective attack angle of the blade cascade and reduce losses. Its characteristic was represented by expanding the positive stall boundary without sacrificing the loss of the design angle of attack, with a maximum reduction of 17.7%. No-angle riblets achieved reduction at a high angle of attack, with a maximum reduction rate of 19.58%. Overall, the reduction effect of diffusion type riblets was better than that of non-angle riblets and better than that of convergence type riblets. In addition, it was found that the width and peak loss of the wake decreased after reduction, and the diffusion line of the wake shifted towards the pressure surface side.
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Key words:
- compressor cascade /
- surface riblets /
- microstructure /
- expand stability /
- loss /
- stall boundary /
- critical Reynolds number
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图 3 叶栅吸力面的分离与再附区的RANS计算结果
Figure 3. Separation and reattachment zones on the suction surface of the blade cascade
图 4 U=78 m/s时的叶片流线的油流显示结果
Figure 4. Oil flow display results of the streamline on the blade surface at U=78 m/s
图 5 基于磨擦速度的雷诺数Reτ分布
Figure 5. Distribution of Reynolds number Reτ based on friction velocity
图 9 失速前后（i=8°～12°）尾迹的总损失分布
Figure 9. Loss distribution in the wake of the blade before and after stall （i=8°—12°）
图 10 叶栅失速后的流动特征及其发展
Figure 10. Flow characteristics and development after stall in a cascade
图 12 U=78 m/s时10°攻角的吸力面流动对比
Figure 12. Comparison of suction surface flow at a 10° angle of attack, when U=78 m/s
图 13 10°攻角叶片表面摩擦力（面A）和涡量沿流向的分量（面B）
Figure 13. Friction force （surface A） and vorticity （plane B） along the flow direction at a 10° angle of attack
图 16 表面脊结构的叶片及其尺寸参数
Figure 16. Blades with surface riblet structures and their size parameters
图 17 不同表面脊结构对叶栅有效正攻角作用效果
Figure 17. Effect of different surface ridge structures on the effective positive angle of attack of the blade cascade
图 18 3种表面脊结构措施相对于原型的损失增长比
Figure 18. Loss growth of three surface ridge structures relative to the original type
图 19 U=78 m/s时，8°攻角下表面脊对尾迹的影响
Figure 19. Influence of surface ridges on wake at an attack angle of 8° when U=78 m/s
图 20 当U=50 m/s时，8°攻角下表面脊对尾迹的影响
Figure 20. Influence of surface ridges on wake at an attack angle of 8° when U=50 m/s
图 21 U=23 m/s时，8°攻角下表面脊对尾迹的影响
Figure 21. Influence of surface ridges on wake at an attack angle of 8° when U=23 m/s
表 1 平板表面脊结构减阻研究的摩擦雷诺数
Table 1. Friction Reynolds numbers for drag reduction study of riblet structures on flat surface
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表 2 叶栅的主要几何参数及边界条件
Table 2. Geometric parameters and boundary conditions of casecade
参数 数值 稠度 1.05 叶高/mm 100 弦长/mm 70 几何入口角/（°） 41.5 几何出口角/（°） 20 叶型弯曲角/（°） 21.5 栅距/mm 66.52 进口总温/K 298.22 出口静压/Pa 96900 雷诺数 235000
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表 3 湍流度Tu测量结果
Table 3. Measurement results of turbulence Tu
来流速度U/（m/s） Tu/% 23 0.910 50 1.042 78 1.207
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