Kameswararao Anupindi

A novel multiblock immersed boundary method for large eddy simulation of complex arterial hemodynamics

Computational fluid dynamics (CFD) simulations are becoming a reliable tool to understand hemodynamics, disease progression in pathological blood vessels and to predict medical device performance. Immersed boundary method (IBM) emerged as an attractive methodology because of its ability to efficiently handle complex moving and rotating geometries on structured grids. However, its application to study blood flow in complex, branching, patient-specific anatomies is scarce. This is because of the dominance of grid nodes in the exterior of the fluid domain over the useful grid nodes in the interior, rendering an inevitable memory and computational overhead. In order to alleviate this problem, we propose a novel multiblock based IBM that preserves the simplicity and effectiveness of the IBM on structured Cartesian meshes and enables handling of complex, anatomical geometries at a reduced memory overhead by minimizing the grid nodes in the exterior of the fluid domain. As pathological and medical device hemodynamics often involve complex, unsteady transitional or turbulent flow fields, a scale resolving turbulence model such as large eddy simulation (LES) is used in the present work. The proposed solver (here after referred as WenoHemo), is developed by enhancing an existing in-house high order incompressible flow solver that was previously validated for its numerics and several LES models by Shetty et al. [Journal of Computational Physics 2010; 229 (23), 8802-8822]. In the present work, WenoHemo is systematically validated for additional numerics introduced, such as IBM and the multiblock approach, by simulating laminar flow over a sphere and laminar flow over a backward facing step respectively. Then, we validate the entire solver methodology by simulating laminar and transitional flow in abdominal aortic aneurysm (AAA). Finally, we perform blood flow simulations in the challenging clinically relevant thoracic aortic aneurysm (TAA), to gain insights into the type of fluid flow patterns that exist in pathological blood vessels. Results obtained from the TAA simulations reveal complex vortical and unsteady flow fields that need to be considered in designing and implanting medical devices such as stent grafts.

Dynamic Mode Decomposition of Fontan Hemodynamics in an Idealized Total Cavopulmonary Connection

Univentricular heart disease is the leading cause of death from any birth defect in the first year of life. Typically, patients have to undergo three open heart surgical procedures within the first few years of their lives to eventually directly connect the superior and inferior vena cavae to the left and right pulmonary arteries forming the Total Cavopulmonary Connection or TCPC. The end result is a weak circulation where the single working ventricle pumps oxygenated blood to the body and de-oxygenated blood flows passively through the TCPC into the lungs. The fluid dynamics of the TCPC junction involve confined impinging jets resulting in a highly unstable flow, significant mechanical energy dissipation, and undesirable pressure loss. Understanding and predicting such flows is important for improving the surgical procedure and for the design of mechanical cavopulmonary assist devices. In this study, Dynamic Mode Decomposition (DMD) is used to analyze previously obtained Stereoscopic Particle Imaging Velocimetry (SPIV) data and Large Eddy Simulation (LES) results for an idealized TCPC. Analysis of the DMD modes from the SPIV and LES serve to both highlight the unsteady vortical dynamics and the qualitative agreement between measurements and simulations.

An embedded flow simulation methodology for flow over fence simulations

In this paper, we report the development of embedding a flow simulation methodology (FSM) (Fasel HF, von Terzi DA, Sandberg RD (2006) A methodology for simulating compressible turbulent flows. J Appl Mech 3:405–412 [1]), (Weinmann M, Sandberg RD, Doolan C (2014) Tandem cylinder flow and noise predictions using a hybrid RANS/LES approach. Int. J. Heat Fluid Flow 50:263–278 [7]) region in a global Reynolds-averaged Navier-Stokes (RANS) region and its application to flow over a fence.

An Embedded LES-RANS Solver for Aerodynamic Simulations

In the current work, we present the development and application of an embedded largeeddy simulation (LES) Reynolds-averaged Navier Stokes (RANS) solver. The novelty of the present work lies in fully embedding the LES region inside a global RANS region. RANS and LES regions are explicitly coupled through arbitrary mesh interfaces and flow and turbulence quantities are exchanged between them as the solution is advanced. A digital filter method extracting mean flow, turbulent kinetic energy and Reynolds stresses from the upstream RANS interface is used to provide meaningful small scale fluctuations to the LES interface. The framework is developed in the open-source computational fluid dynamics software OpenFOAM. The embedding approach is validated by simulating a spatially developing turbulent channel flow. Thereafter, flow over a surface mounted spanwiseperiodic vertical fence is simulated to demonstrate the importance of DFM and the effect of the location of the RANS-LES interface. In each case, both mean and second-order statistics are compared with the direct numerical simulation (DNS) data from the literature. The streamwise evolution of skin friction coefficient on the wall is compared with the DNS result and the attachment point of the primary recirculation zone behind the fence matches the reference data well. Results indicate that by feeding synthetic turbulence at the LES interface a good match can be obtained for the mean flow quantities. However, in order to obtain a good match for the Reynolds stresses the LES interface needs to be placed sufficiently far upstream, which in the present case was six spoiler-heights before the fence.

High-Order Large Eddy Simulation of Flow in Idealized and Patient-Specific Total Cavopulmonary Connections

The Fontan procedure is used in pediatric situations in which infants have complex congenital heart disease or a single effective ventricle. This procedure by-passes right heart by connecting the left and right pulmonary arteries (LPA/RPA) to the superior and inferior vena cavae (SVC/IVC). The resulting reconstructed anatomy is called total cavopulmonary connection or TCPC. Knowledge of fluid dynamics in TCPC helps in optimizing the connection itself for reduced resistance as well as aids in designing cavopulmonary assist devices like viscous impeller pump (VIP) [1].© 2011 ASME

Modeling of Patient-Specific Fontan Physiology From MRI Images for CFD Testing of a Cavopulmonary Assist Device

Single ventricle heart disease is a congenital condition characterized by the inoperability of one ventricle of an infant’s heart. Those suffering from this condition face a series of palliative surgeries called the Fontan procedure, which bypasses the non-functional ventricle by creating a total cavopulmonary connection, or TCPC. This TCPC forms from the anastomosis of the superior and inferior vena cavae (SVC, IVC) to the left and right pulmonary arteries (LPA, RPA), thus allowing systemic blood flow to bypass the heart and flow passively to the lungs. The Fontan procedure creates this junction with three surgeries separated by months or years.© 2011 ASME