基于高频响TR-PIV流场测量和传声器阵列脉动压力同步测量的仿仙人柱圆柱流动控制机理的实验研究

In a view to perform a series of fundamental experimental investigations on flow control mechanism of cactus-shaped cylindrical structure, which have exhibited amazing passive flow control ability in deserts due to natural selection, two state-of-the-art fluid mechanics diagnosis instrumentations, i.e., high-repetition Time-resolved Particle Image Velocimetry (TR-PIV), and a microphone array, will be synchronized to measure the instantaneous velocity field and wall-pressure-fluctuations, respectively. Through preliminary wind tunnel tests, dynamic and static drag & lift forces of two types of cylindrical structures, i.e., cactus-shaped cylinders with V-grooves and a smooth cylinder, will be measured to select the optimized V-grooves (number & depth) and determine the typical Reynolds numbers for further insight investigation. Subsequently, the flows around two cylindrical configurations at typical Reynolds numbers will be measured in low-speed wind tunnel for comparative studies, resulting in a wealth of unsteady information of the instantaneous velocity fields and wall-pressure-fluctuations. Based on the experimental data, extensive signal analyses like cross-correlation, coherence and wavelet analysis will be performed to reveal the underlying correlation between the unsteady flow field and wall-pressure-fluctuations; two advanced data-driven algorithms, i.e., Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD), will be employed to identify and determine spatio-temporal variations of coherent structures superimposed in the unsteady flow field, separated region, and the wake patterns. The comprehensive analysis on the basis of the unsteady measurements would give a sound explanation of flow-control mechanism of the cactus-shaped cylinder, as well as the magic natural selection of the Saguaro cactus. This would result in a promising bio-inspired methodology for flow control of cylindrical structures, which have seen widespread uses in the industry.

本项目集成高频响TR-PIV瞬态流场测试技术和传声器阵列壁面脉动压力场测试技术，实现两者同步采样，以开展仿仙人柱圆柱流动控制的基础实验研究。在低速风洞中，首先通过动静态升阻力实验测量，对仿仙人柱V形槽圆柱模型和光滑圆柱模型在一系列雷诺数下的流动进行对比实验，挑选出优化的V形槽布置方式，并确定典型雷诺数工况供后续实验研究。采用瞬态流场-脉动压力场同步测量系统，测得若干典型雷诺数下两类圆柱模型绕流中的瞬态流场和壁面脉动压力场，通过互相关分析、相干谱分析和时频联合分析获得两者之间的响应关系；采用先进的本征正交模态分解算法POD和动态模态分解算法DMD，提取非定常流场中的主要旋涡结构，获得流动分离区域特性、尾流区流动特征和旋涡结构时空演化特征，深入揭示仿仙人柱V形槽柱体流动控制的机理，为自然选择形成的仙人柱表面特征提供科学的流体力学解释。相关成果可为工程应用提供一种有效的仿生力学手段。

在流体力学工程应用和基础研究中，圆柱结构流动控制问题非常重要。毫无疑问，寻找合适的减阻方法和流致振动抑制手段十分值得研究。在自然界中，漫长的自然选择进化过程使得许多植物自身分别具有优越的被动流动控制能力，才使其在许多特殊的环境条件下得以长期生存和生长。针对这些自然界中的流动控制成功案例，选择性地深入研究相关流体动力学特性，以获取其流动控制物理机制，将具有很强的科学意义和工程应用价值。本项目集成高频响TR-PIV瞬态流场测试技术和传声器阵列壁面脉动压力场测试技术，实现两者同步采样，以开展仿仙人柱圆柱流动控制的基础实验研究。在低速风洞中，首先通过动静态升阻力实验测量，对仿仙人柱V形槽圆柱模型和光滑圆柱模型在一系列雷诺数下的流动进行对比实验，挑选出优化的V形槽布置方式，并确定典型雷诺数工况供后续实验研究。采用瞬态流场-脉动压力场同步测量系统，测得若干典型雷诺数下两类圆柱模型绕流中的瞬态流场和壁面脉动压力场，通过互相关分析、相干谱分析和时频联合分析获得两者之间的响应关系；采用先进的本征正交模态分解算法POD和动态模态分解算法DMD，提取非定常流场中的主要旋涡结构，获得流动分离区域特性、尾流区流动特征和旋涡结构时空演化特征，深入揭示了仿仙人柱V形槽柱体流动控制的机理，为自然选择形成的仙人柱表面特征提供科学的流体力学解释。相关成果可为工程应用提供一种有效的仿生力学手段。