The work focuses on the analysis of the flow fields in the Food and Drug Administrations (FDA) 'Critical Path' benchmark blood pump. The CAD model of the pump is an opensource material, so the thesis works started with the mesh generation. A block-structured hexahedral mesh has been created using ANSYS ICEM CFD 15.0. An unsteady (URANS) incompressible blood flow simulation has been performed using k-ω SST turbulence model, with one of the operating conditions prescribed by the experimental literature. The simulations were performed using ANSYS CFX 19.1 solver. The validated results for the flow field show promising results in the blade passage region and the diffuser regions but the pressure head obtained has some discrepancies which were analyzed and justified. In addition, a study on hemolysis prediction using Power Law was performed, and the blood damage values of the benchmark blood pump were calculated for the stress-based model in the Eulerian approach.
The role of Computational Fluid Dynamics (CFD) in the biomedical field has increased a lot in recent years. The problems related to biocompatibility in medical and biological industries capture the attention of CFD engineers. One such biocompatible device is a Ventricular Assist Device (VAD). The development phase of VAD's associates CFD to make it more robust. VADs generally incorporated with blood pumps, so it is essential to examine the dynamics of the blood flow in the pump and also to analyze the damages concerned with the blood cells.
The U.S. Food and Drug Administration (FDA)and the Center of Devices and Radiological Health (CDRH) have sponsored certain CFD'round-robins' to validate the efficiency of computer simulations in biomedical applications. The ‘Computational round-robin #2’ concerns with a 'Critical Path' benchmark blood Pump.
Table of Contents
1 Introduction
1.1 Ventricular Assist Device
1.2 History of VADs
1.3 Operating Conditions for VAD
1.4 Role of Computational Fluid Dynamics
2 Literature Review
2.1 Blood
2.1.1 Red Blood Cells
2.2 Blood Rheology
2.3 Blood damage
2.4 Numerical Hemolysis Prediction
3 Description of Turbulence Modeling
3.1 RANS/URANS
3.1.1 Shear Stress Transport model
4 Experimental Study
5 Pre-Processing
5.1 Structure of FDA blood pump
5.2 Mesh Information
5.2.1 Mesh Overview
5.2.2 Mesh Generation
6 Computation
7 Results and Discussion
7.1 Convergence
7.2 Pressure Head
7.3 Flow Field
7.4 Wall Shear Stress and Hemolysis Comparison
8 Conclusion
Research Objectives and Key Topics
This thesis aims to validate the effectiveness of Computational Fluid Dynamics (CFD) in analyzing hemodynamics and predicting hemolysis within the FDA’s "Critical Path" benchmark blood pump. By performing unsteady incompressible flow simulations and comparing the results against experimental data, the research evaluates the accuracy of current numerical methods and turbulence modeling in a biomedical context.
- Hemodynamic performance analysis of rotary blood pumps
- Implementation of block-structured mesh generation for complex geometries
- Application of URANS and the k-ω SST turbulence model
- Comparative study of hemolysis prediction using Power Law models
- Validation of CFD results against PIV experimental benchmarks
Excerpt from the Thesis
2.4 Numerical Hemolysis Prediction
Giersiepen and Wurzinger, 1990 made the base foundation for the numerical hemolysis prediction. This model is the widely used hemolysis prediction model, commonly known as Power Law Model. This model develops a power law function for the damage fraction, in other words, it is a simple relation between the magnitude of shear stress, exposure time and hemolysis [23].
Where Hb/Hb released hemoglobin in percentage, τ is the shear stress and t is the exposure time, and (C, α, β) are constants [23].
This model has a shear stress covering range up to 255 Pa and exposure time up to 700 ms, the constants used by Giersiepen et al. were (C, α, β) (3.63 10−7, 2.416, 0.785) [23] respectively. From the blood damage correlation of Giersiepen and Wurzinger many methods have been evolved. Arora et al. [21] found that in the real flow this model has a very poor prediction. Results obtained from this model has a variation of 1 to 2 in magnitude from the measured values. Some researchers claim that the values of the constants are the reason for this poor prediction. From Zhang et al. [25], and Heuser and Optiz [24], the constants in Giersiepen and Wurzinger model, were obtained from a Couette type device, which uses mechanical seal so there may be an over-prediction of blood damage. These researchers introduced certain alterations made in the experimental setup and various new sets of constants were published.
Summary of Chapters
1 Introduction: Provides an overview of heart failure, the necessity of VADs, and the specific role of CFD in improving blood pump design.
2 Literature Review: Discusses the rheological properties of blood, the mechanisms of blood damage, and existing numerical approaches for hemolysis prediction.
3 Description of Turbulence Modeling: Explains the theoretical framework behind RANS and URANS, focusing on why the k-ω SST model was selected.
4 Experimental Study: Summarizes the inter-laboratory PIV experimental setup and the protocols used to create validation data for the FDA benchmark pump.
5 Pre-Processing: Details the CAD geometry, the mesh generation process using ICEM CFD, and the considerations for near-wall refinement.
6 Computation: Outlines the boundary conditions, solver settings, and numerical schemes used within ANSYS CFX to run the transient simulation.
7 Results and Discussion: Analyzes convergence, pressure head, velocity fields, and compares numerical results with empirical benchmarks.
8 Conclusion: Synthesizes findings on the accuracy of CFD simulations and suggests areas for future improvement in hemolysis modeling.
Keywords
Computational Fluid Dynamics, Ventricular Assist Device, Blood pump, block-structured hexahedral mesh, URANS, k-ω SST, hemolysis, Power Law, stress-based model, Eulerian approach, Hemodynamics, FDA benchmark, Numerical simulation, Pressure head, Wall shear stress.
Frequently Asked Questions
What is the primary focus of this master's thesis?
The thesis focuses on using Computational Fluid Dynamics (CFD) to analyze flow fields and predict hemolysis within the FDA’s "Critical Path" benchmark blood pump.
What are the main research themes?
The work covers mesh generation for complex geometries, the application of URANS turbulence models, validation against PIV experimental data, and the implementation of stress-based blood damage models.
What is the main objective of this study?
The goal is to test the credibility and accuracy of CFD simulations in predicting flow patterns and hemolysis compared to established experimental results for the FDA blood pump.
Which scientific methods were applied?
The study utilizes URANS simulations with the k-ω SST turbulence model and the Power Law model for Eulerian hemolysis prediction.
What is addressed in the main part of the thesis?
The main part covers the literature review on blood rheology, detailed mesh generation, numerical computation steps in ANSYS CFX, and a comprehensive discussion of the resulting flow fields and shear stress.
Which keywords best describe this research?
Key terms include Computational Fluid Dynamics, Ventricular Assist Device, hemolysis, URANS, and the k-ω SST turbulence model.
Why is hemolysis prediction critical for VAD development?
High shear stress within blood pumps can cause the rupture of red blood cells, leading to hemolysis; predicting this is vital to ensuring device hemocompatibility for patients.
How did the author handle the discrepancy in pressure head results?
The author discusses that discrepancies likely stem from turbulence model selection and uncertainties in Reynolds numbers identified in inter-laboratory experimental studies.
- Arbeit zitieren
- Krishnaraj Narayanaswamy (Autor:in), 2019, Numerical Flow Simulation in FDA's "Critical Path" benchmark blood pump, München, GRIN Verlag, https://www.grin.com/document/915240
