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Article

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

[+] Author and Article Information
Steven W. Day1

The University of Virginia, Charlottesville, VA 22903sday@alumni.virginia.edu

James C. McDaniel

The University of Virginia, Charlottesville, VA 22903

1

Corresponding author. Current address: Section of Evolution & Ecology, University of California, One Shields Avenue, Davis, CA 95616.

J Biomech Eng 127(2), 244-253 (Nov 18, 2004) (10 pages) doi:10.1115/1.1865189 History: Received October 07, 2003; Revised September 20, 2004; Accepted November 18, 2004

Abstract

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.

FIGURES IN THIS ARTICLE
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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

Figure 7

Example of instantaneous u˜ (left) and fluctuation u (right) velocity field for the blade configuration at 6L∕min at the midblade height with contours of vorticity shown for the fluctuation velocity field

Figure 8

Distribution of mean speed within the cutwater for flowrates of 3, 6, and 9L∕min. One plane of constant z, at cutwater centerline, and several planes of constant x are shown.

Figure 9

Distribution of rms of fluctuating speed (left) and MRSS (right) within the cutwater for flow rates of 3, 6, and 9L∕min within the cutwater center plane

Figure 2

Distribution of mean velocity within the inlet elbow for flow rates of 3, 6, and 9L∕min. One plane of constant x, at inlet center plane (left), and several planes of constant y (right) are shown. Labels on the axes are the exact distance from a common origin located on the axis of rotation of the impeller. The entire square representing that particular grid point is colored a constant shade, resulting in the appearance of pixels in the plot. The pixels are the size of the resolution of the measurement.

Figure 3

Distribution of rms of velocity (left) and MRSS (right) within the inlet elbow for flow rates of 3, 6, and 9L∕min at inlet center plane

Figure 4

Examples of instantaneous u˜ (top) and fluctuation u (bottom) velocity field in the inlet elbow at steady flow rate of 6L∕min taken at two different instants in time. Contours of speed (magnitude of the instantaneous or fluctuation velocity).

Figure 5

Distribution of mean velocity within the blade passage for flow rates of 3, 6, and 9L∕min. One plane of constant z at midblade height (left) and several planes of constant y are shown. Location of the two blades defining the blade passage are shown as black lines. The location of the impeller OD is shown as a grey line. Blade rotation is clockwise, so pressure side of blade is just below upper blade and suction side is just above lower blade. Within the blade passage, velocity is relative to the impeller rotation. For all radii greater than impeller OD, absolute velocity is shown.

Figure 6

Distribution of rms of velocity (left) and MRSS (right) within the blade passage for flow rates of 3, 6, and 9L∕min at midblade height

Figure 1

Cutaway view of the pump showing regions of interest and location of laser sheets that define the measurement planes for three-measurement configurations. Flow enters the inlet cannula from the left ventricle and passes into the blade passages. Fluid exiting the impeller is collected in the exit volute and flows past the cutwater to the exit of the pump. Measurement planes labeled as IE, inlet elbow; BP, blade passage; and CW, cutwater.

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