Press Room - Flow characteristics in a centrifugal blood pump

Flow characteristics in a centrifugal blood pump

COBE Cardiovascular and CD-adapco recently teamed together to simulate flow through COBE Cardiovascular’s centrifugal blood pump, the Revolution. These efforts were used to identify potential problems and to aid future designs.

Common problems possible with blood pumps are hemolysis and/or thrombus formation. High shear stress and a tortuous flow path are two conditions that can cause hemolysis. Thrombus formation is a complex function ofphysiological conditions, biocompatibility of blood-contacting surfaces, and the fluid dynamic characteristics of blood flow within a flow domain. Generally, thrombus formation occurs in regions of high shear stress, turbulence and/or poor blood biocompatibility followed by exposure to regions of re-circulation (i.e. vortices) and/or stagnation.

Flow through the Revolution was modeled assuming Newtonian behavior. Although blood is a non-Newtonian fluid, under certain circumstances its flow behavior can be approximated by a Newtonian model (e.g. flow with high Reynolds number such as flow through arteries). Figure 1 displays the boundary and inlet conditions.

A 3-D, transient, moving mesh analysis was used to calculate the flow field. The inside of the pump rotates while the body of the pump remains stationary. Figure 2 shows the meshed flow domain for the pump. For this analysis, the solver ran on six parallel Linux processors for approximately 30 days, yielding a resolved, transiently cyclic solution.

Figures 3 and 4 are snapshots of the primed pump after the rotors have spun 335° and show areas where vortices were anticipated. From a top view, fixed reference frame (Figure 3), no vortices are apparent. Figure 4 gives the relative velocity over the cross section of part of a vane (relative velocity with respect to the spinning impeller). No vortices are seen there either. Analysis of pressure leads to similar results. Similar velocity and pressure analysis' were performed on several areas within the pump.

Particle pathline projections were also obtained. The projection indicated that particles entering the flow domain do not follow a tortuous path through the pump. Thus, it is believed that the residence time through the pump is minimal.

The lack of tortuosity and vortices in critical areas indicate that the possibility of hemolysis and thrombus formation is low. Any potentially troublesome areas identified by the model have since then been redesigned and tested. STAR-CD has been an invaluable tool for identifying problems, confirming designs, and providing insights into future designs of this centrifugal blood pump.

Fig 1: The revolution pumping conditions
Boundary Conditions
Blue: stationary
Green: rotates at 2000 rpm
Inlet Conditions
Density: 1.049 g/cm3
Viscosity: .0024 Pals
Temperature: 37 °C
Flow: 3.2 lpm
Figs 2a &2b: Mesh used to analyze the revolution
Fig 2a: 750,000 fluid cells (trim, prism, hex cells), Moving Mesh Analysis (ASI)
Fig 2b: Pump Rotor Surface Mesh
Fig 3: Velocity magnitude taken in absolute reference frame
Fig 4: Relative velocity taken at the cross section of one vane