Abstract The impact of flow-normal ribs and small-scale surface roughness on the drag and vortex shedding of a circular cylinder was investigated. Three rib heights, four relative rib spacings and three different forms of micro-roughness were combined to produce 28 unique surface coatings for the cylinder. The drag was measured in a wind tunnel for Reynolds numbers in the range 20,000 R e 160,000 , representing nearly a decade change centred about the drag crisis. The drag measurements were complemented by hot-wire measurements in the wake to investigate the vortex shedding frequency. The results show significant average drag reduction, up to 23%, for most of the ribbed geometries compared to a smooth cylinder for R e 160,000 . Increasing the rib height was found to reduce the critical Reynolds number and increase the minimum drag coefficient. Varying the rib spacing resulted in an ‘‘optimal” spacing, approximately five times the rib height, that caused the lowest critical Reynolds number. Increasing the micro-roughness resulted in a reduction in the critical Reynolds number and an increase in the minimum drag coefficient.

中文翻译：

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加强筋和小尺度粗糙度对气缸阻力危机的显着影响

摘要 研究了流动法向肋和小尺度表面粗糙度对圆柱阻力和涡流脱落的影响。三个肋高度、四个相对肋间距和三种不同形式的微观粗糙度相结合，为气缸生产了 28 种独特的表面涂层。阻力是在风洞中测量的，雷诺数范围为 20,000 Re 160,000，代表了以阻力危机为中心的近十年变化。阻力测量由尾流中的热线测量补充，以研究涡旋脱落频率。结果表明，与 Re 160,000 的光滑圆柱相比，大多数带肋几何形状的平均阻力显着降低了 23%。发现增加肋的高度会降低临界雷诺数并增加最小阻力系数。改变肋间距会产生一个“最佳”间距，大约是肋高度的五倍，这导致了最低的临界雷诺数。增加微观粗糙度导致临界雷诺数减少和最小阻力系数增加。