Title: Understanding the effect of wall elasticity in turbulent channel flows Show Chinese title

Title: 理解壁面弹性在湍流通道流动中的影响

Abstract: This study compares turbulent channel flows over elastic walls with those over rough walls, to explore the role of the dynamic change of shape of the wall on turbulence. The comparison is made meaningful by generating rough walls from instantaneous configurations of the elastic cases. The aim of this comparison is to individually understand the role of fluid-structure interaction effects and the role of wall shape/undulations in determining the overall physics of flow near elastic walls. With an increase in the compliance of the wall, qualitatively similar trends for many of the effects produced by a rough wall are also seen in the elastic wall. However, specific features can be observed for the elastic wall cases only, arising from the mutual interaction between the solid and fluid, leading to a further increase in drag. To understand them, we look at the turbulent structures, which exhibit clear differences across the various configurations: roughness induces only a slight reduction of streamwise coherency, resulting in a situation qualitatively similar to what is found in classical turbulent channel flows, whereas elasticity causes the emergence of a novel dominant spanwise coherency. Additionally, we explored the effect of vertical disturbances on elastic wall dynamics by comparing with permeable walls having similar (average) wall-normal velocity fluctuations at the interface. The permeable walls were found to have minimal similarities with elastic walls. Overall, we can state that the wall motion caused by the complex fluid-structure interaction contributes significantly to the flow and must be considered when modeling it. In particular, we highlight the emergence of strong wall-normal fluctuations near the wall, which result in strong ejection events, an attribute not observed for rigid walls. Show Chinese abstract

Abstract: 本研究比较了弹性壁面和粗糙壁面上的湍流通道流动，以探讨壁面形状动态变化在湍流中的作用。 通过从弹性情况的瞬时配置生成粗糙壁面，使这种比较具有意义。 这种比较的目的是单独理解流体-结构相互作用效应以及壁面形状/波动在决定弹性壁面附近整体流动物理特性中的作用。 随着壁面柔性的增加，许多由粗糙壁面产生的效应也表现出定性相似的趋势。 然而，仅在弹性壁面情况下可以观察到特定特征，这些特征源于固体与流体之间的相互作用，导致阻力进一步增加。 为了理解这些现象，我们观察了湍流结构，它们在不同配置中表现出明显的差异：粗糙度仅引起流向相干性的轻微减少，导致一种定性上类似于经典湍流通道流动的情况；而弹性则导致了一种新的主导横向相干性的出现。 此外，我们通过与具有相似（平均）界面法向速度脉动的多孔壁面进行比较，探讨了垂直扰动对弹性壁面动力学的影响。 发现多孔壁面与弹性壁面之间仅有极少的相似性。 总体而言，我们可以指出，由复杂的流体-结构相互作用引起的壁面运动对流动有显著影响，在建模时必须考虑这一点。 特别是，我们强调了靠近壁面处强烈的法向波动的出现，这些波动导致强烈的喷射事件，这是刚性壁面所没有的属性。