Grid-Induced Numerical Errors for Shear Stresses and Essential Flow Variables in a Ventricular Assist Device: Crucial for Blood Damage Prediction?

2018 ◽  
Vol 3 (4) ◽  
Author(s):  
Lucas Konnigk ◽  
Benjamin Torner ◽  
Sebastian Hallier ◽  
Matthias Witte ◽  
Frank-Hendrik Wurm
Keyword(s):  
Shear Stress ◽  
Prediction Models ◽  
Stokes Equations ◽  
Grid Size ◽  
Blood Pump ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Damage Prediction ◽  
Blood Damage ◽  
Stress Calculation

Adverse events due to flow-induced blood damage remain a serious problem for blood pumps as cardiac support systems. The numerical prediction of blood damage via computational fluid dynamics (CFD) is a helpful tool for the design and optimization of reliable pumps. Blood damage prediction models primarily are based on the acting shear stresses, which are calculated by solving the Navier–Stokes equations on computational grids. The purpose of this paper is to analyze the influence of the spatial discretization and the associated discretization error on the shear stress calculation in a blood pump in comparison to other important flow quantities like the pressure head of the pump. Therefore, CFD analysis using seven unsteady Reynolds-averaged Navier–Stokes (URANS) simulations was performed. Two simple stress calculation indicators were applied to estimate the influence of the discretization on the results using an approach to calculate numerical uncertainties, which indicates discretization errors. For the finest grid with 19 × 106 elements, numerical uncertainties up to 20% for shear stresses were determined, while the pressure heads show smaller uncertainties with a maximum of 4.8%. No grid-independent solution for velocity gradient-dependent variables could be obtained on a grid size that is comparable to mesh sizes in state-of-the-art blood pump studies. It can be concluded that the grid size has a major influence on the shear stress calculation, and therefore, the potential blood damage prediction, and that the quantification of this error should always be taken into account.

Influence of turbulent shear stresses on the numerical blood damage prediction in a ventricular assist device

2019 ◽  
Vol 42 (12) ◽  
pp. 735-747 ◽  
Author(s):  
Benjamin Torner ◽  
Lucas Konnigk ◽  
Frank-Hendrik Wurm
Keyword(s):  
Shear Stress ◽  
Equivalent Stress ◽  
Volumetric Analysis ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Ventricular Assist ◽  
Damage Prediction ◽  
Blood Damage ◽  
Damage Models ◽  
Order Of Magnitude

The blood damage prediction in rotary blood pumps is an important procedure to evaluate the hemocompatibility of such systems. Blood damage is caused by shear stresses to the blood cells and their exposure times. The total impact of an equivalent shear stress can only be taken into account when turbulent stresses are included in the blood damage prediction. The aim of this article was to analyze the influence of the turbulent stresses on the damage prediction in a rotary blood pump’s flow. Therefore, the flow in a research blood pump was computed using large eddy simulations. A highly turbulence-resolving setup was used in order to directly resolve most of the computed stresses. The simulations were performed at the design point and an operation point with lower flow rate. Blood damage was predicted using three damage models (volumetric analysis of exceeded stress thresholds, hemolysis transport equation, and hemolysis approximation via volume integral) and two shear stress definitions (with and without turbulent stresses). For both simulations, turbulent stresses are the dominant stresses away from the walls. Here, they act in a range between 9 and 50 Pa. Nonetheless, the mean stresses in the proximity of the walls reach levels, which are one order of magnitude higher. Due to this, the turbulent stresses have a small impact on the results of the hemolysis prediction. Yet, turbulent stresses should be included in the damage prediction, since they belong to the total equivalent stress definition and could impact the damage on proteins or platelets.

Large eddy simulation in a rotary blood pump: Viscous shear stress computation and comparison with unsteady Reynolds-averaged Navier–Stokes simulation

2018 ◽  
Vol 41 (11) ◽  
pp. 752-763 ◽  
Author(s):  
Benjamin Torner ◽  
Lucas Konnigk ◽  
Sebastian Hallier ◽  
Jitendra Kumar ◽  
Matthias Witte ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Blood Pump ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Element Mesh ◽  
Damage Prediction ◽  
Eddy Simulation ◽  
Viscous Shear ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

Purpose: Numerical flow analysis (computational fluid dynamics) in combination with the prediction of blood damage is an important procedure to investigate the hemocompatibility of a blood pump, since blood trauma due to shear stresses remains a problem in these devices. Today, the numerical damage prediction is conducted using unsteady Reynolds-averaged Navier–Stokes simulations. Investigations with large eddy simulations are rarely being performed for blood pumps. Hence, the aim of the study is to examine the viscous shear stresses of a large eddy simulation in a blood pump and compare the results with an unsteady Reynolds-averaged Navier–Stokes simulation. Methods: The simulations were carried out at two operation points of a blood pump. The flow was simulated on a 100M element mesh for the large eddy simulation and a 20M element mesh for the unsteady Reynolds-averaged Navier-Stokes simulation. As a first step, the large eddy simulation was verified by analyzing internal dissipative losses within the pump. Then, the pump characteristics and mean and turbulent viscous shear stresses were compared between the two simulation methods. Results: The verification showed that the large eddy simulation is able to reproduce the significant portion of dissipative losses, which is a global indication that the equivalent viscous shear stresses are adequately resolved. The comparison with the unsteady Reynolds-averaged Navier–Stokes simulation revealed that the hydraulic parameters were in agreement, but differences for the shear stresses were found. Conclusion: The results show the potential of the large eddy simulation as a high-quality comparative case to check the suitability of a chosen Reynolds-averaged Navier–Stokes setup and turbulence model. Furthermore, the results lead to suggest that large eddy simulations are superior to unsteady Reynolds-averaged Navier–Stokes simulations when instantaneous stresses are applied for the blood damage prediction.

Quantitative Analysis of Reynolds and Navier–Stokes Based Modeling Approaches for Isothermal Newtonian Elastohydrodynamic Lubrication

2021 ◽  
Vol 143 (12) ◽  
Author(s):  
Leoluca Scurria ◽  
Tommaso Tamarozzi ◽  
Oleg Voronkov ◽  
Dieter Fauconnier
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Thickness Distribution ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Low Viscosity ◽  
Fluid Film Thickness

Abstract When simulating elastohydrodynamic lubrication, two main approaches are usually followed to predict the pressure and fluid film thickness distribution throughout the contact. The conventional approach relies on the Reynolds equation to describe the thin lubricant film, which is coupled to a Boussinesq description of the linear elastic deformation of the solids. A more accurate, yet a time-consuming method is the use of computational fluid dynamics in which the Navier–Stokes equations describe the flow of the thin lubricant film, coupled to a finite element solver for the description of the local contact deformation. This investigation aims at assessing both methods for different lubrication conditions in different elastohydrodynamic lubrication (EHL) regimes and quantify their differences to understand advantages and limitations of both methods. This investigation shows how the results from both approaches deviate for three scenarios: (1) inertial contributions (Re > 1), i.e., thick films, high speed, and low viscosity; (2) high shear stresses leading to secondary flows; and (3) large deformations of the solids leading to inaccuracies of the Boussinesq equation.

PIV Measurements of Flow in a Centrifugal Blood Pump: Steady Flow

2004 ◽  
Vol 127 (2) ◽  
pp. 244-253 ◽  
Author(s):  
Steven W. Day ◽  
James C. McDaniel
Keyword(s):  
Shear Stress ◽  
Artificial Heart ◽  
Heart Valves ◽  
Blood Pump ◽  
Reynolds Stresses ◽  
Centrifugal Blood Pump ◽  
Flow Rates ◽  
Blood Damage ◽  
Artificial Heart Valves ◽  
Stagnant Flow

Magnetically suspended left ventricular assist devices have only one moving part, the impeller. The impeller has absolutely no contact with any of the fixed parts, thus greatly reducing the regions of stagnant or high shear stress that surround a mechanical or fluid bearing. Measurements of the mean flow patterns as well as viscous and turbulent (Reynolds) stresses were made in a shaft-driven prototype of a magnetically suspended centrifugal blood pump at several constant flow rates (3–9L∕min) using particle image velocimetry (PIV). The chosen range of flow rates is representative of the range over which the pump may operate while implanted. Measurements on a three-dimensional measurement grid within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser are reported. The measurements are used to identify regions of potential blood damage due to high shear stress and∕or stagnation of the blood, both of which have been associated with blood damage within artificial heart valves and diaphragm-type pumps. Levels of turbulence intensity and Reynolds stresses that are comparable to those in artificial heart valves are reported. At the design flow rate (6L∕min), the flow is generally well behaved (no recirculation or stagnant flow) and stress levels are below levels that would be expected to contribute to hemolysis or thrombosis. The flow at both high (9L∕min) and low (3L∕min) flow rates introduces anomalies into the flow, such as recirculation, stagnation, and high stress regions. Levels of viscous and Reynolds shear stresses everywhere within the pump are below reported threshold values for damage to red cells over the entire range of flow rates investigated; however, at both high and low flow rate conditions, the flow field may promote activation of the clotting cascade due to regions of elevated shear stress adjacent to separated or stagnant flow.

The turning couples on an elliptic particle settling in a vertical channel

1994 ◽  
Vol 271 ◽  
pp. 1-16 ◽  
Author(s):  
Peter Y. Huang ◽  
Jimmy Feng ◽  
Daniel D. Joseph
Keyword(s):  
Shear Stress ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Vertical Channel ◽  
Navier Stokes ◽  
Front Face ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Back Face ◽  
The One

We do a direct two-dimensional finite-elment simulation of the Navier–Stokes equations and compute the forces which turn an ellipse settling in a vertical channel of viscous fluid in a regime in which the ellipse oscillates under the action of vortex shedding. Turning this way and that is induced by large and unequal values of negative pressure at the rear separation points which are here identified with the two points on the back face where the shear stress vanishes. The main restoring mechanism which turns the broadside of the ellipse perpendicular to the fall is the high pressure at the ‘stagnation point’ on the front face, as in potential flow, which is here identified with the one point on the front face where the shear stress vanishes.

scholarly journals Off-Design Performance Prediction for Radial-Flow Impellers

1988 ◽  
Author(s):  
Shen C. Lee ◽  
Daying Chen
Keyword(s):  
Stokes Equations ◽  
Mechanical Energy ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Pump Impeller ◽  
Navier Stokes Equations ◽  
Measured Velocity ◽  
Production Water ◽  
Performance Predictions ◽  
Stream Functions

A numerical method was developed to consider the two-dimensional flowfield between impeller blades of a given geometry. Solution of the laminar Navier-Stokes equations in geometry-oriented coordinates was obtained for stream functions and vorticities. Velocities and pressures were calculated to determine the output fluid-energy head. The circumferential components of the normal and shear stresses along the blade were evaluated to give the input mechanical-energy head. Performance predictions were obtained for different load conditions. Comparisons were made with the measured velocity vectors of the flowfield of an air-pump impeller and with the measured performance of a production water pump, good agreements were reached.

scholarly journals Effects of surfactant on propagation and rupture of a liquid plug in a tube

2019 ◽  
Vol 872 ◽  
pp. 407-437 ◽  
Author(s):  
M. Muradoglu ◽  
F. Romanò ◽  
H. Fujioka ◽  
J. B. Grotberg
Keyword(s):  
Shear Stress ◽  
Evolution Equations ◽  
Stokes Equations ◽  
Thin Liquid Film ◽  
Front Tracking ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Liquid Plug ◽  
Front Tracking Method ◽  
Airway Walls

Surfactant-laden liquid plug propagation and rupture occurring in lower lung airways are studied computationally using a front-tracking method. The plug is driven by an applied constant pressure in a rigid axisymmetric tube whose inner surface is coated by a thin liquid film. The evolution equations of the interfacial and bulk surfactant concentrations coupled with the incompressible Navier–Stokes equations are solved in the front-tracking framework. The numerical method is first validated for a surfactant-free case and the results are found to be in good agreement with the earlier simulations of Fujioka et al. (Phys. Fluids, vol. 20, 2008, 062104) and Hassan et al. (Intl J. Numer. Meth. Fluids, vol. 67, 2011, pp. 1373–1392). Then extensive simulations are performed to investigate the effects of surfactant on the mechanical stresses that could be injurious to epithelial cells, such as pressure and shear stress. It is found that the liquid plug ruptures violently to induce large pressure and shear stress on airway walls and even a tiny amount of surfactant significantly reduces the pressure and shear stress and thus improves cell survivability. However, addition of surfactant also delays the plug rupture and thus airway reopening.

NUMERICAL ANALYSIS OF AN AXIAL BLOOD PUMP WITH DIFFERENT IMPELLER BLADE HEIGHTS

2012 ◽  
Vol 12 (03) ◽  
pp. 1250045 ◽  
Author(s):  
JIAXING QI ◽  
YANHONG ZHOU ◽  
DONGFANG WANG ◽  
LIANG ZHONG
Keyword(s):  
Shear Stress ◽  
Flow Rate ◽  
Reverse Flow ◽  
Blood Pump ◽  
Shear Stresses ◽  
Cfd Simulations ◽  
Impeller Blade ◽  
Rotating Speed ◽  
Shear Stress Level ◽  
Computational Fluid Dynamics Cfd

Computational fluid dynamics (CFD) simulations of the flow in an axial blood pump with different blade heights (BH150, BH200 and BH250) were performed in the present study. The flow in the pump was assumed as steady and turbulent, and blood was treated as incompressible and Newtonian fluid. The flow rate increased with the rise in blade heights. At the impeller rotating speed of 20,000 rpm and a pressure of 100 mm Hg, the pump produces a flow rate up to 5 L/min in BH200 and BH250 models. The reverse flow and vortices have been identified in the BH150 and BH200 models in the outlet regions, but not for BH250 model. The high shear stress of the flow in the pump mainly occurred at the blade tips. The BH200 model achieved an expected flow rate up to 5 L/min with 90% of the shear stresses less than 500 Pa and the exposure time less than 22 ms, which has the acceptable shear stress level in the literature.

Aerodynamic and Aeroacoustic Analyses of a Regenerative Blower

2015 ◽  
Author(s):  
Man-Woong Heo ◽  
Tae-Wan Seo ◽  
Chung-Suk Lee ◽  
Kwang-Yong Kim
Keyword(s):  
Shear Stress ◽  
Variational Formulation ◽  
Stokes Equations ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Side Channel ◽  
Leakage Flow ◽  
Navier Stokes Equations ◽  
Unsteady Flow Analysis

This paper presents a parametric study to investigate the aerodynamic and aeroacoustic characteristics of a side channel regenerative blower. Flow analysis in the side channel blower was carried out by solving three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence closure. Aeroacoustic analysis was conducted by solving the variational formulation of Lighthill’s analogy on the basis of the aerodynamic sources extracted from the unsteady flow analysis. The height and width of the blade and the angle between inlet and outlet ports were selected as three geometric parameters, and their effects on the aerodynamic and aeroacoustic performances of the blower have been investigated. The results showed that the aerodynamic and aeroacoustic performances were enhanced by decreasing height and width of blade. It was found that angle between inlet and outlet ports significantly influences the aerodynamic and aeroacoustic performances of the blower due to the stripper leakage flow.

Eulerian-Eulerian Multiphase Modeling of Blood Cells Segregation in Flow Through Microtubes

2017 ◽  
Author(s):  
Yertay Mendygarin ◽  
Luis R. Rojas-Solórzano ◽  
Nurassyl Kussaiyn ◽  
Rakhim Supiyev ◽  
Mansur Zhussupbekov
Keyword(s):  
Shear Stress ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Heart Diseases ◽  
Accurate Determination ◽  
Shear Stresses ◽  
High Shear ◽  
Blood Damage ◽  
Solid Phases

Cardiovascular Diseases, the common name for various Heart Diseases, are responsible for nearly 17.3 million deaths annually and remain the leading global cause of death in the world. It is estimated that this number will grow to more than 23.6 million by 2030, with almost 80% of all cases taking place in low and middle income countries. Surgical treatment of these diseases involves the use of blood-wetted devices, whose relatively recent development has given rise to numerous possibilities for design improvements. However, blood can be damaged when flowing through these devices due to the lack of biocompatibility of surrounding walls, thermal and osmotic effects and most prominently, due to the excessive exposure of blood cells to shear stress for prolonged periods of time. This extended exposure may lead to a rupture of membrane of red blood cells, resulting in a release of hemoglobin into the blood plasma, in a process called hemolysis. Moreover, exposure of platelets to high shear stresses can increase the likelihood of thrombosis. Therefore, regions of high shear stress and residence time of blood cells must be considered thoroughly during the design of blood-contacting devices. Though laboratory tests are vital for design improvements, in-vitro experiments have proven to be costly, time-intensive and ethically controversial. On the other hand, simulating blood behavior using Computational Fluid Dynamics (CFD) is considered to be an inexpensive and promising tool to help predicting blood damage in complex flows. Nevertheless, current state-of-the-art CFD models of blood flow to predict hemolysis are still far from being fully reliable and accurate for design purposes. Previous work have demonstrated that prediction of hemolysis can be dramatically improved when using a multiphase (i.e., phases are plasma, red blood cells and platelets) model of the blood instead of assuming the blood as a homogeneous mixture. Nonetheless, the accurate determination of how the cells segregate becomes the critical issue in reaching a truthful prediction of blood damage. Therefore, the attempt of this study is to develop and validate a numerical model based on Granular Kinetic Theory (GKT) for solid phases (i.e., cells treated as particles) that provides an improved prediction of blood cells segregation within the flow in a microtube. Simulations were based on finite volume method using Eulerian-Eulerian modeling for treatment of three-phase (liquid-red blood cells and platelets) flow including the GKT to deal with viscous properties of the solid phases. GKT proved to be a good model to predict particle concentration and pressure drop by taking into account the contribution of collisional, kinetic and frictional effects in the stress tensor of the segregated solid phases. Preliminary results show that the improved segregated model leads to a better prediction of spatial distribution of blood cells. Simulations were performed using ANSYS FLUENT platform.

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