Collaborative Research: Kinetic-based self-transitioning turbulence modeling for pulsatile flows

脉动流在自然界和工程系统中无处不在。了解脉动流动中的湍流对于知识进步和技术创新都是至关重要的。然而，由于缺乏合适的湍流计算模型来解决脉动过程中从层流到湍流再回到层流过程中固有的不稳定性，因此仍然存在挑战。目前流行的层流、过渡流或由静止管流发展而来的湍流准则不适用于脉动流，现有的基于Kolmogorov理论的湍流模型也不适用于充分发展的湍流。在实验室实验的支持下，本项目旨在建立一种新的时间脉动流的自转换湍流模拟方法。这项研究的一个重要影响将是基于图像的精准医学对心血管疾病的特定患者的无创诊断和评估。该项目将为研究生/本科生提供多学科培训的机会，并为印第安纳大学-普渡大学印第安纳波利斯分校和纽约城市学院制定课程提供各种机会。该项目的目标是开发和验证一个新的基于动力学的自过渡湍流模型，用于求解脉动流动中的层流-湍流-层流转变，其中，当空间或时间分辨率不足以/足以分辨整个尺度范围时，当流动在脉动中加速/减速时，对小尺度运动的建模需求被自动激活/停用。将显式滤波应用于过渡流中的分辨率解，以使次网格尺度模型适应动态的时间和空间分辨率要求。将亚网格尺度模型嵌入到基于动力学的格子Boltzmann方法中，通过在图形处理单元上进行大规模并行化来获得破坏性的快速计算速度。通过并行的数值模拟和实验室实验，将深入了解脉动流动中的湍流在惯性和粘性效应、脉动频率、几何曲率和分叉的各种影响下的情况。非定常脉动流中层流、过渡流和湍流行为的一般标准将被揭示，这些标准对于脉动流的基于软件的计算流体力学至关重要，传统上，层流或湍流必须在模拟之前被预先定义。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。

Pulsatile flows are omnipresent in nature and engineering systems. Understanding turbulence in pulsatile flows is critically important to both knowledge advancement and technological innovation. However, challenges have remained due to the lack of appropriate turbulence computational models that solve the inherent unsteadiness with successive transitions from laminar to turbulent, and then back to laminar flow during pulsation. The prevailing flow criteria of either laminar, or transitional, or turbulent flow developed from stationary pipe flows are not appropriate for pulsatile flows; the existing turbulence models based on Kolmogorov theory for fully-developed turbulence are not suitable, either. With the support of laboratory experiment, this project is to establish a new self-transitioning turbulence modeling method for time-wise pulsatile flows. An important impact of this research will be on the precision medicine of image-based patient-specific noninvasive diagnose and assessment of cardiovascular diseases. The project will provide various opportunities for multidisciplinary training for graduate/undergraduate students, as well as for curriculum development at both Indiana University-Purdue University, Indianapolis and City College of New York. The goal of this project is to develop and validate a new kinetic-based self-transitional turbulence model for solving the laminar-turbulent-laminar transition in pulsatile flows, in which the need of modeling for small scale motion is automatically activated/deactivated when the spatial or temporal resolution is insufficient/sufficient to resolve the entire range of scales when flow is accelerating/decelerating in a pulsation. Explicit filtering is applied to resolved-scale solutions in transitional flows to adapt the sub-grid scale model to dynamic temporal and spatial resolution requirements. The sub-grid scale model is embedded in the kinetic-based lattice Boltzmann method to achieve disruptively fast computation speed through massive parallelization on graphic processing units. In-depth understanding of turbulence in pulsatile flows under various influences of inertia and viscous effects, pulsating frequency, geometric curvature and bifurcations will be explored through concurrent numerical simulation and laboratory experiment. General criteria of laminar, transitional, and turbulent behaviors in unsteady pulsatile flows will be unveiled, which are critically important to software-based computational fluid dynamics for pulsatile flows where, conventionally, laminar or turbulent flow must be predefined before the simulation.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.