条带型粗糙度的线性模型
Linear models of strip-type roughness
AI总结：
本文提出线性化RANS与Spalart-Allmaras模型耦合的框架，研究条带型粗糙度引起的二次流，发现条带宽度约为半通道高度0.7倍时二次流最强，并识别出两种诱发机制。
摘要：
本文利用Zampino等人(2022)提出的线性化雷诺平均纳维-斯托克斯方法，研究了由横向变化粗糙度产生的普朗特第二类二次流。动量方程与Spalart-Allmaras模型耦合，同时通过将针对均匀粗糙度建立的策略适配到非均匀表面来捕捉粗糙度效应。对控制方程进行线性化，得到一个框架，能够在粗糙度属性横向小变化的极限情形下，快速探索与非均匀表面相关的参数空间。研究考虑通道流动，其中纵向高、低粗糙度条带对称排列。通过改变条带宽度，发现线性机制在决定二次流的尺寸和强度方面起主导作用。在此背景下，二次流可解释为湍流平均流对由壁面非均匀性产生的稳态强迫的时间平均输出响应。事实上，线性模型预测，当条带宽度约为半通道高度的0.7倍时，二次流最为强烈，这与现有数据高度吻合。此外，本文讨论了一个统一框架，用于分析应用中常见的非均匀粗糙度属性与横向变化地形的组合。注意到该框架假设表面属性横向变化较小，识别出两种独立的二次流诱发源机制，即湍流结构发展所依赖的虚拟原点的横向变化，以及流向速度滑移的横向变化，后者捕捉了非平面地形波谷和波峰处主体流动所感受到的加速/减速效应。
英文摘要：
Prandtl's secondary flows of the second kind generated by laterally-varying roughness are studied using the linearised Reynolds-Averaged Navier-Stokes approach proposed in Zampino et al (2022). The momentum equations are coupled to the Spalart-Allmaras model while the roughness is captured by adapting established strategies for homogeneous roughness to heterogeneous surfaces. Linearisation of the governing equations yields a framework that enables a rapid exploration of the parameter space associated with heterogeneous surfaces, in the limiting case of small spanwise variations of the roughness properties. Channel flow is considered, with longitudinal high and low roughness strips arranged symmetrically. By varying the strip width, it is found that linear mechanisms play a dominant role in determining the size and intensity of secondary flows. In this setting, secondary flows may be interpreted as the time-averaged output response of the turbulent mean flow subjected to a steady forcing produced by the wall heterogeneity. In fact, the linear model predicts that secondary flows are most intense when the strip width is about 0.7 times the half-channel height, in excellent agreement with available data. Furthermore, a unified framework to analyse combinations of heterogeneous roughness properties and laterally-varying topographies, common in applications, is discussed. Noting that the framework assumes small spanwise variations of the surface properties, two separate secondary-flow inducing source mechanisms are identified, i.e. the lateral variation of the virtual origin from which the turbulent structure develops and the lateral variation of the streamwise velocity slip, capturing the acceleration/deceleration perceived by the bulk flow over troughs and crests of non-planar topographies.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
