Direct Numerical Simulation of Pulsating Flow in Curved Pipes: Insights into Aortic Dissection in Humans

Author

Gokul Anugrah Gopakumar, Univeristy of KentuckyFollow

Author ORCID Identifier

https://orcid.org/0009-0005-7383-799X

Date Available

11-19-2025

Year of Publication

2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Engineering (DEng)

College

Engineering

Department/School/Program

Mechanical Engineering

Faculty

Christoph Brehm

Faculty

Jonathan F. Wenk

Abstract

This dissertation investigates the hemodynamics of pulsating blood flow in curved vessels through direct numerical simulations (DNS), with the overarching aim of uncovering fluid dynamic mechanisms linked to the onset and progression of aortic dissection in humans. The work is structured in two parts: (i) fundamental studies in idealized geometries and (ii) preliminary investigations in patient-specific anatomies. In the first part, curved pipe models representing the aortic arch are used to isolate the effects of pulsation frequency, amplitude ratio, and curvature ratio on transitional and turbulent flow dynamics. The simulations reveal that curvature-driven centrifugal forces shift the peak velocity toward the outer wall, while transition is initiated on the inner wall in regions of low velocity. Dean vortex breakdown is shown to be highly sensitive to pulsation amplitude and vessel curvature, with higher values accelerating turbulence onset compared to steady or low-amplitude conditions. These changes strongly affect the topology of coherent and stochastic fluctuations, as quantified by the Reynolds stress tensor. Hemodynamic metrics of direct clinical interest, including time-averaged wall shear stress (TASS) and pressure gradients, exhibit distinct spatial variations. Elevated TASS is consistently localized along the outer downstream wall of the arch, coinciding with regions most vulnerable to Type B dissection in vivo. In the second part, preliminary patient-specific simulations were performed with physiologically realistic inflow and outflow boundary conditions, where volumetric flow rates were tuned through Windkessel models to approximate systemic circulation. The first set of simulations was compared against Doppler ultrasound measurements, demonstrating good agreement in velocity profiles. A more detailed investigation was then carried out using time-resolved 4D flow MRI data, with direct comparisons of velocity fields and volumetric flow rates showing strong consistency between simulation and imaging. While quantities such as time-averaged wall shear stress (TASS) and oscillatory shear index (OSI) were not directly validated in the patient-specific cases, insights into these clinically relevant metrics were drawn from the canonical curved pipe studies. Together, these efforts highlight the feasibility of combining fundamental DNS with imaging-based validation to better understand patient-specific hemodynamic environments. By uniting mechanistic insights from canonical curved pipe flows with patient-specific validation studies, this work provides a comprehensive framework for understanding the interplay between vascular geometry, pulsatile flow physics, and hemodynamic stresses implicated in aortic dissection. The results highlight how curvature and unsteadiness shape the onset of turbulence, alter near-wall shear stresses, and redistribute pressure fields, ultimately offering new perspectives on the fluid dynamic precursors of vascular disease.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.516

Funding Information

University of Kentucky Igniting Research Collaborations program, having the grant number 1013176655.

Recommended Citation

Gopakumar, Gokul Anugrah, "Direct Numerical Simulation of Pulsating Flow in Curved Pipes: Insights into Aortic Dissection in Humans" (2025). Theses and Dissertations--Mechanical Engineering. 249.
https://uknowledge.uky.edu/me_etds/249