Influence of geometry, rheology and compliance on the transition to turbulence in pulsatile pipe flow

几何形状、流变性和柔顺性对脉动管流湍流过渡的影响

• 批准号: 418015548
• 负责人: Professor Dr. Marc Avila Canellas
• 金额: --
• 依托单位: Zentrum für angewandte Raumfahrttechnologie und Mikrogravitation (ZARM)
• 依托单位国家: 德国
• 项目类别: Research Units
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/418015548?language=en
• 关键词: Influence; geometry; rheology; compliance; transition

The presence of disturbed flow patterns in the cardiovascular system is thought to trigger diseases. Therefore, in recent years there has been an increasing interest on understanding under what conditions instabilities and turbulence transition occur in the cardiovascular system. Apart from the inherent difficulties of studying transition even in canonical systems, cardiovascular flow includes several additional complexities. Blood flow in the large arteries is pulsatile, the arteries are flexible and exhibit complex geometries, and blood itself is a non-Newtonian fluid. Some of these features have been investigated in the literature, usually separately and in simple setups. The effect of the pulsation has been mostly studied in straight and smooth rigid pipes. Even in this canonical system, transition is greatly affected by the pulsation. Depending on the flow parameters, frequency and shape of the pulsation, the flow can be highly susceptible to the sudden appearance of turbulence during certain phases of the pulsation. This is even more so for flows driven with physiological waveforms, suggesting that turbulence could be more widespread in the cardiovascular system than what was previously thought. The influence of flexible walls and non-Newtonian fluids on pulsatile pipe flow has received little attention in the literature. While both compliance and e.g., shear-thinning rheology usually delay turbulence transition in steady pipe flow, in the pulsatile case their effects remain largely unknown. The goal of this project is to extend the knowledge gained on turbulence transition in pulsatile pipe flows in rigid pipes, and systematically study one additional feature of cardiovascular flow. Three different problems are considered. Firstly, pulsatile flow in straight pipes with flexible walls. Secondly, pulsatile flow of complex fluids in rigid pipes. Thirdly, pulsatile flow in simple geometries which resemble certain sections of the human aorta. The focus will be on determining if each new feature affects the critical mechanism identified for the simple case, or if it even introduces new critical paths to turbulence. In order to do so we will develop numerical tools to perform transient growth analyses, and adapt pre-existing software to perform direct numerical simulations. Direct comparisons to laboratory experiments within the research unit will be performed. The ultimate, long-term goal is to define a complete roadmap to turbulence in the cardiovascular system and model it in a simple way using the experimental and numerical results.

心血管系统中流动模式的存在被认为会引发疾病。因此，近年来，在心血管系统中发生不稳定性和湍流转变，人们对理解的兴趣越来越大。除了在规范系统中研究过渡的固有困难外，心血管流程还包括其他几个复杂性。大动脉中的血流是脉动的，动脉是柔性的，并且表现出复杂的几何形状，而血液本身是一种非牛顿液。这些功能中的一些通常在文献中进行了研究，通常是在简单的设置中进行的。脉动的效果主要是在笔直和光滑的刚性管道中研究的。即使在这个规范系统中，过渡也受到脉动的极大影响。根据流量参数，脉动的频率和形状，流动可能非常容易受到脉动某些阶段中湍流突然出现的影响。对于用生理波形驱动的流动，这甚至更是如此，这表明湍流在心血管系统中可能比以前的想法更广泛。柔性壁和非牛顿流体对脉冲管流的影响很少在文献中受到关注。虽然依从性和例如，剪切薄的流变学通常会延迟稳定管流中的湍流转变，但在脉冲情况下，它们的效果在很大程度上尚不清楚。该项目的目的是扩展有关刚性管道中脉冲管流中湍流过渡的知识，并系统地研究心血管流动的另一个特征。考虑了三个不同的问题。首先，脉冲流在具有柔性壁的直管中流动。其次，刚性管中复杂流体的脉冲流动。第三，简单几何形状中的脉冲流，类似于人主动脉的某些部分。重点将放在确定每个新功能是否会影响简单情况下确定的关键机制，或者它甚至引入了湍流的新关键途径。为此，我们将开发数值工具来执行瞬态增长分析，并适应先前的软件来执行直接的数值模拟。将进行与研究单元内实验实验的直接比较。最终的长期目标是定义心血管系统中湍流的完整路线图，并使用实验和数值结果以简单的方式对其进行建模。