Computational Fluid Dynamics of Gap Flow in a Biocentrifugal Blood Pump

Abstract

The centrifugal blood pump with a magnetically suspended impeller has shown its superiority as compared to other artificial heart pumps. However, there is still insufficient understanding of fluid mechanics related issues in the clearance gap. The design nature of the pump requires sufficient washout in the clearance between the impeller and the stationary pump housing inner surface. In this study, numerical simulations were carried out to investigate the flow fields in the gap of the Kyoto-NTN centrifugal blood pump. The flow patterns in the gap region of the blood pump were presented and regions of high and low velocity were identified. It was found that the radial velocity of the blood in the gap was closely related to the pressure distribution at the exit of the impeller, both the highest pressure gradient and the highest radial velocity in the gap occurred at an angular position of 170 degrees . The mass flow rate in the gap was estimated to be 25.2% of the pump outflow, which is close to the measurement results of a five times enlarged test pump. The wall shear stresses on the gap surface were found to be over 21 Pa and below 300 Pa, which is correspondingly higher than the threshold of thrombi formation and is lower than the shearing threshold of red blood cells. Comparison of the 1 : 1 simulation model with the measurement results on a five times enlarged test pump indicates that there are some differences in the resulting radial velocity distributions in the gap and thus the washout mechanism. Two symmetrical high washout regions at both the cutwater and splitter plate were observed in the simulation instead of a single washout region at the splitter plate found in the experimental study. This may be due to the scaling effect of the enlarged test pump; also the medium used in the experiment is different from the simulation.

The use of computational fluid dynamics in the development of ventricular assist devices

“…The implementations of these CFD packages are either based on the finite volume23 method or finite element method. Fluent 36, 37, 38, 39, 40, 41 and CFX 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 11, 57, 58, 59, both available from ANSYS, Inc. (Canonsburg, PA) and STAR-CD from CD-Adapco 60, 61 (Melville, New York) are the CFD software packages used most often for analysis and modelling of blood flow in VADs. In addition, AcuSolve from ACUSIM Software 62 (Mountain View, CA) and Adina from Adina R&D (Watertown, MA) are also used.…”

Parameter estimation and statistical analysis on frequency-dependent active control forces

“…Active magnetic bearings (AMB) have been receiving widespread applications in industry [1][2][3][4][5][6]. This is because they can support the rotor without contact, thus no friction and heat are generated and the need for lubrication is also eliminated.…”

Computational Study of Magnetically Suspended Centrifugal Blood Pump (The First Report: Main Flow and Gap Flow)

“…Therefore, it can be thought that the leakage flow counteracts against the tendency of pressure increase in the low flow area which is shown in the pump characteristics (Fig.4). In addition, Chua et al (13) reported that Q L /Q I was 20% (Q I =6.3 L/min, Q L =1.3 L/min) at S L =0.20 mm.…”

“…According to the structure, this pump is classified as a low specific speed and low Reynolds number pump; the studies regarding such pumps conducted by Kurokawa et al [9], [10] and Matsui et al [11] may be interesting. Chua et al [12], [13] performed a numerical simulation of the internal flow when the shape of the blade was different from that of this pump, and reported that the internal flow changed according to the position of the blade due to the different velocity or pressure distribution and that the amount of flow which went through the gap corresponded to about 20% of the flow expelled by the impeller. However, there is no report which explains how the gap flow, which is characteristic to this pump, affects the entire pump system.…”