通过主动表面形态变化利用非对称粗糙度在球体上产生升力
Lift generation on a sphere through asymmetric roughness using active surface morphing
AI总结：
本文通过实验研究一侧光滑、一侧带凹坑的球体在不同雷诺数和凹坑深度比下的非对称粗糙度升力效应，揭示了最优凹坑深度随雷诺数的变化规律及流动分离机制，为钝体尾流控制和实时机动奠定基础。
摘要：
本研究探讨了一种通过在球体表面以气动方式操控其表面拓扑结构并形成非对称粗糙度分布，从而在球体周围产生升力的新现象。针对雷诺数（$Re = U_{\infty} d/ν$，其中 $U_{\infty}$ 为流体速度，$d$ 为球体直径，$ν$ 为流体运动粘度）范围从 $6\times10^4$ 到 $1.3\times10^5$，以及凹坑深度比（$k/d$，其中 $k$ 为凹坑深度）从 $0$ 到 $1\times10^{-2}$ 的条件，利用一个一侧光滑、一侧带凹坑的智能可变形球体，开展了一系列系统的实验。结果表明，非对称粗糙球体可产生高达阻力 80% 的升力，与马格努斯效应所产生的升力相当。凹坑深度比既影响升力开始产生时的 $Re$，也影响可达到的最大升力系数（$C_L$）。实现最大升力的最优 $k/d$ 随 $Re$ 变化：在低 $Re$ 下需要更深的凹坑，而在高 $Re$ 下较浅的凹坑更有效。对于固定的 $Re$，增大 $k/d$ 会使升力单调增加，直到达到临界 $k/d$，超过该临界值后升力下降。粒子图像测速（PIV）结果表明，凹坑延迟了粗糙侧的流动分离，而光滑侧保持不变，从而形成非对称的边界层分离，导致尾流偏转并产生升力。超过临界 $k/d$ 后，流动分离位置向上游移动，增大了尾部尾流的尺寸，减小了尾流偏转，从而使升力降低。总体而言，本研究为钝体尾流控制奠定了基础，并为实时机动应用铺平了道路。
英文摘要：
This study investigates a novel phenomenon of lift generation around a sphere by pneumatically manipulating its surface topology with an asymmetric roughness distribution. A comprehensive series of systematic experiments were conducted for Reynolds numbers ($Re = U_{\infty} d/ν$, where $U_{\infty}$ is the fluid velocity, $d$ is the sphere diameter, and $ν$ is the fluid kinematic viscosity) ranging from $6\times10^4$ to $1.3\times10^5$, and dimple depth ratios ($k/d$, where $k$ is the dimple depth) from $0$ to $1\times10^{-2}$ using a smart morphable sphere with one smooth and one dimpled side. The findings show that an asymmetrically rough sphere can generate lift forces up to 80\% of the drag, comparable to those produced by the Magnus Effect. The dimple depth ratio affects both the $Re$ at which lift generation begins and the maximum lift coefficient ($C_L$) achievable. The optimal $k/d$ for maximum lift varies with $Re$: deeper dimples are needed at low $Re$, while shallower dimples are more effective at high $Re$. For a fixed $Re$, increasing $k/d$ monotonically increases lift until a critical $k/d$ is reached, beyond which lift decreases. Particle Image Velocimetry (PIV) revealed that dimples delay flow separation on the rough side while the smooth side remains unchanged, resulting in asymmetric boundary layer separation, leading to wake deflection and lift generation. Beyond the critical $k/d$, the flow separation location moved upstream, increasing the size of the rear wake, reducing wake deflection, and thus decreasing lift. Overall, this study establishes the foundation for wake control over bluff bodies and paves the way for real-time manoeuvring applications.
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