Theory and Experiments for Distributed Roughness Effects in Laminar Boundary Layers

识别和模拟分布的表面粗糙度对层流边界层的影响是基础流体力学中的一个重要挑战。它的技术相关性与表面粗糙度在预测飞机表面摩擦、风力涡轮机发电量和类似空气动力系统的性能中所起的作用有关。虽然空气动力学粗糙度已被研究了近一个世纪，但人们对其作用的认识还不够深入。一个原因可能是，大多数研究都是从孤立的粗糙度元素开始的，试图建立从单一元素到多个元素的理解。这项研究将寻求另一种方法，使用一种称为三层渐近性的分析技术来处理整个分布粗糙度领域。分析结果将与使用3D打印制造的粗糙度场的风洞测量结果进行比较。此外，该项目将为南得克萨斯州具有STEM兴趣的高中生提供独特的教育体验。这些经验将集中在量纲分析和缩放的关键技能，低于风洞测试的有用性的关键工程概念，以及三层渐近分析。为了开发一种全场方法，该项目将追求三个研究目标。首先，将实现基于三层渐近分析的理论模型。该模型将适应线性和非线性幅度范围内的分布粗糙度。在一个很容易获得超级计算机级数值解的时代，这种技术并没有得到广泛的应用。然而，渐近分析非常适合于研究分布粗糙度，因为需要参数研究来表征许多粗糙度场。其次，风洞测量将在为验证理论预测的关键方面而设计的人造粗糙度试件上进行。第三，验证后的模型将被用来进行参数研究，探索广泛的粗糙度结构，并促进对分布粗糙度的新理解。将渐近分析与验证实验相结合，然后使用经过验证的工具来执行广泛的参数研究，将极大地促进对粗糙度问题的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Identifying and modeling how distributed surface roughness affects laminar boundary layers is an important challenge in fundamental fluid mechanics. Its technological relevance relates to the role surface roughness plays in predicting aircraft skin friction, wind-turbine power production, and the performance of similar aerodynamic systems. Although aerodynamic roughness has been studied for nearly a century, a good understanding of its role has not yet been achieved. One reason may be that most studies have started from isolated roughness elements and attempted to build understanding from single elements to multiple elements. This research will pursue an alternative approach that addresses an entire field of distributed roughness using an analysis technique known as triple-deck asymptotics. The analytical results will be compared to wind-tunnel measurements of roughness fields to be manufactured using 3D printing. Additionally, the project will provide unique educational experiences for South Texas high-school students with STEM interests. These experiences will focus on the critical skills of dimensional analysis and scaling, key engineering concepts that underly the usefulness of both wind-tunnel testing, and triple-deck asymptotic analysis.To develop a whole-field approach, this project will pursue three research objectives. First, a theoretical model based on triple-deck asymptotic analysis will be implemented. This model will accommodate distributed roughness in both linear and nonlinear amplitude ranges. This technique is not widely used in an era of easy access to supercomputer-class numerical solutions. However, asymptotic analysis is ideally suited to studying distributed roughness because parameter studies are needed to characterize many roughness fields. Second, wind-tunnel measurements will be made over manufactured roughness specimens designed to validate key aspects of the theoretical predictions. Third, the validated model will be used to perform a parameter study that explores a wide range of roughness configurations and advances a new understanding of distributed roughness. Combining asymptotic analysis with validation experiments and then using the validated tool to perform wide-ranging parameter studies will significantly advance understanding of the roughness problem.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.