I ntroduction

IIntroductionntroduction As a viable alternative to heart transplantation we have designed a

fully implantable axial flow ventricular assist device for long-term mechanical circulatory support.

UVA1UVA1 Axial Flow Pump Axial Flow Pump The flow path of this hydraulically efficient device has a smooth,

streamlined, one pass blood flow path that facilitates continuous washing of all surfaces contacting blood.

Magnetically Levitated Impeller

Tubular Axial Configuration

Methods:Methods:

ResultsResults ConclusionsConclusionsUVA1UVA1 design included the extensive use of CFD performance modeling, including steady and transient flow conditions.

The diffuser flow path geometry was modified by varying only two design parameters in order to satisfy the objective function selected.

This iterative design optimization procedure led to a diffuser configuration characterized by a smooth flow profile with no obvious signs of stagnation or recirculation regions.

As formulated, this optimization problem can be implemented into an automatic design optimization package, having the potential to significantly reduce the design timeline.

Performance results for UVA1 design support proceeding with manufacturing of a titanium prototype for extensive mock loop characterization and initial acute animal testing.

CFD AnalysisCFD AnalysisFull pump model was developed in BladeGen (CFX-ANSYS).Grid generation software GridPro used for high quality structured elements.Grid quality and convergence studies were completed.800,000 grid elements.Grid refinement for regions expected to have large gradients

CFDCFDModelModel

Blood Properties: Newtonian assumption; fluid viscosity of 0.0035 kg/m*s; fluid density of 1050 kg/m3.

Nominal design point: 4.5 lpm,100 mmHg and 6,500 rpm.

Operating range: 2 to 8 lpm, 70 to 140 mmHg, speeds of 5,000 to 8,000 rpm.

Implantable Dimensions: 90 mm by 35 mm 6 Stationary Inducer Blades, 4 Rotating Impeller

Blades, 3 Stationary Diffuser Blades.

AlexandrinaAlexandrina UntaroiuUntaroiu11, Houston G. Wood, Houston G. Wood1 1 , Paul E. Allaire, Paul E. Allaire11 , , Curt G. TribbleCurt G. Tribble22 1Mechanical and Aerospace Engineering, University of Virginia and 2College of Medicine, University of Florida

Design parametersDesign parameters: axial length of diffuser blade, trailing edge angle to adjust the curvature of the blade

Objective functionObjective function to be minimized: blood damage index- Particles released at inlet of CFD model

- Fluid stress and time tracked along streaklines- Damage index calculated at each discrete node in the grid- Summation of all indices yields a total damage index (‘probability’ of trauma)

ConstraintConstraint of optimization problem: prescribed range for pressure difference across the computational model

UVA1 External View

Influence of geometric parameters on local flow dynamics

Minimizing Irregular Flow Patterns in the Diffuser Section of an Axial Flow Blood PumpMinimizing Irregular Flow Patterns in the Diffuser Section of an Axial Flow Blood Pump

UVA1 - Sectioned Assembly with Impeller

Diffuser

Impeller

Inducer

The diffuser section has a significant impact on overall hydraulic performance of the device. Irregular flow patterns in this region are difficult to remove since a very limited number of geometric parameters can be modified without completely compromising diffuser efficiency. This study details the diffuser design configuration and the optimization method developed to achieve a smooth flow profile.

Optimization ProblemOptimization Problem

CFD model implemented in Ansys-CFX, solver of the Reynolds-Averaged Navier Stokes (RANS) equations.

Flow field parameters estimated for a wide range of operating conditions. Irregular flow patterns with potential negative impact on blood (stagnation,

recirculation, and flow separation regions) have been investigated. The influence of geometric parameters on the local flow dynamics and overall

pump performance has been assessed based on detailed parametric studies.

= scalar stress, = scalar stress, t = exposure timet = exposure timeFull CFD ModelFull CFD Model

Magnitude of VelocitiesMagnitude of Velocities

Optimized diffuser designOptimized diffuser designDiffuser with five blades, minimal curvature of blade, and variable lengthDiffuser with five blades, minimal curvature of blade, and variable length

rotating flow component is not rotating flow component is not completely removedcompletely removed

large stagnation regions at TElarge stagnation regions at TE

Diffuser with three blades and gradually increased curvatureDiffuser with three blades and gradually increased curvature

recirculation regionrecirculation region smaller region of recirculationsmaller region of recirculation

Streamlines illustrating recirculationStreamlines illustrating recirculation Flow profileFlow profile

no obvious signs of irregular flow patternsno obvious signs of irregular flow patterns

Streamlines colored according to the exposure timeStreamlines colored according to the exposure time