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.

心血管系统中血流模式紊乱被认为会引发疾病。因此，近年来，人们对了解心血管系统在什么条件下发生不稳定和湍流转变越来越感兴趣。除了在规范系统中研究转变的固有困难之外，心血管血流还包括一些额外的复杂性。大动脉中的血流是脉动的，动脉是灵活的并且呈现出复杂的几何形状，并且血液本身是非牛顿流体。其中一些功能已在文献中进行过研究，通常是单独且简单的设置。脉动的影响主要在直且光滑的刚性管道中进行研究。即使在这个规范系统中，转变也会受到脉动的很大影响。根据脉动的流动参数、频率和形状，在脉动的某些阶段，流动非常容易受到突然出现的湍流的影响。对于由生理波形驱动的流动来说更是如此，这表明湍流在心血管系统中可能比之前想象的更广泛。柔性壁和非牛顿流体对脉动管流的影响在文献中很少受到关注。虽然顺应性和剪切稀化流变学通常会延迟稳定管流中的湍流转变，但在脉动情况下，它们的影响在很大程度上仍然未知。该项目的目标是扩展在刚性管道中脉动管流的湍流转变方面获得的知识，并系统地研究心血管流的另一项特征。考虑三个不同的问题。首先，具有柔性壁的直管中的脉动流。其次，刚性管道中复杂流体的脉动流动。第三，简单几何形状的脉动流，类似于人类主动脉的某些部分。重点将在于确定每个新特征是否会影响为简单情况确定的关键机制，或者是否会引入新的湍流关键路径。为此，我们将开发数值工具来执行瞬态增长分析，并调整现有软件来执行直接数值模拟。将与研究单位内的实验室实验进行直接比较。最终的长期目标是定义心血管系统湍流的完整路线图，并使用实验和数值结果以简单的方式对其进行建模。