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

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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.