王延青 1张园园 2刘悦 2李牧 2刘涛 2翁鼎 2汪家道2
作者信息
- 1. 浙江清华长三角研究院,浙江 嘉兴 314006
- 2. 清华大学高端装备界面科学与技术全国重点实验室,北京 100084
- 折叠
摘要
Abstract
Aerodynamic drag reduction remains a pivotal research frontier in fluid mechanics,demonstrating significant application potential in fields such as aviation,high-speed trains and sports equipment.Surface morphology drag reduction is one of the critical methods in aerodynamic drag reduction and has attracted extensive attention from researchers due to its significant practical value.Aerodynamic drag can be systematically categorized into two distinct types of frictional drag(induced by viscous shear stresses)and pressure drag(caused by flow separation and adverse pressure gradients).The work aims to introduce the analytical methods in aerodynamic drag reduction,elucidate the drag reduction mechanisms and morphological parameters of various surface texture strategies,and discuss their respective application scenarios and potential future research directions.
Methodologically,wind tunnel experiments and numerical simulations are effective approaches in drag reduction research.Wind tunnel experiments can be used to directly assess the drag reduction performance of test objects through force sensors,and also obtain flow field information with techniques like Particle Image Velocimetry(PIV)and anemometers.However,the design of drag reduction wind tunnel experiments is relatively complex,with limited flow field data acquisition.Additionally,factors such as system vibrations and sensor placement may affect measurement accuracy.In contrast,numerical simulations provide more comprehensive flow field details.Common turbulence models in numerical methods include Reynolds-averaged Navier-Stokes(RANS)models,Large Eddy Simulation(LES),and Direct Numerical Simulation(DNS).These numerical approaches can more intuitively reveal the drag reduction mechanisms of surface structures.
Surface morphology achieves aerodynamic frictional drag reduction by changing turbulent boundary layer states.Ribs,bio-inspired by shark skin,are widely studied and their shapes include triangular,semicircular,rectangular,and blade-like geometries.Studies indicate that blade-shaped ribs achieve the optimal drag reduction performance.Beyond geometry,dimensional parameters,specifically rib height and inter-rib spacing(typically expressed as dimensionless wall units h+and s+),critically affect effectiveness.The research demonstrates that the most effective configuration occurs at h+=s+≈ 10.Two theories explain the working principle of ribs.The Protrusion Height Theory suggests that the drag reduction comes from directional flow differences.The Secondary Vortex Theory focuses on how rib-generated vortices interact with main turbulent flows.Separately,spanwise grooves use trapped vortices to reduce friction through an"air bearing"effect.Researchers are optimizing groove shapes,depth-width ratios,and layouts to keep vortices stable while lowering pressure drag.These improvements aim to balance vortex behavior and pressure effects for real-world aerodynamic applications.
For bluff bodies lacking streamlined profiles,aerodynamic pressure drag dominates due to flow separation,with research primarily focusing on separation suppression.Since turbulent boundary layers exhibit delayed separation points compared to laminar flows,surface modifications aim to promote turbulence transition.Common approaches include random roughness,dimpled surfaces,and groove structures,though random roughness suffers from uncontrollable parameters and potential drag penalties.Regular dimpled surfaces overcome these limitations,demonstrating remarkable drag reduction in sphere and cylinder experiments by energizing boundary layers through vortex generation.The Reynolds number range for effective drag reduction depends critically on dimple dimensions and distribution density.Alternatively,spanwise grooves also facilitate boundary layer transition while exhibiting relatively shape-insensitive performance characteristics.
Surface topography fabrication is a core technology for aerodynamic drag reduction.Main methods include mechanical machining,imprinting,3D printing,and laser processing.Mechanical machining suits geometrically simple surfaces with larger features.Imprinting excels at large-scale and curved surface preparation.3D printing flexibly replicates biomimetic structures,while laser processing enables micron-scale drag-reducing features,particularly useful for hydrophobic surfaces.
Despite notable advancements in surface drag reduction technologies,key challenges persist.For frictional drag reduction,designing effective structures for large surfaces with spatially varying flow conditions remains difficult,and scalable manufacturing methods for textured surfaces require further development.In pressure drag reduction,the size and distribution of surface structures critically determine their applicability,necessitating deeper investigation into quantitative relationships between microstructural parameters and drag reduction performance across operational scenarios.关键词
气动减阻/表面结构/摩擦阻力/压差阻力Key words
aerodynamic drag reduction/surface structure/frictional drag/pressure drag分类
机械制造
