Computational Fluid Dynamics Performance Prediction for the Hydrodynamic Bearings of the VentrAssist Rotary Blood Pump *Christopher D. Bertram, *Yi Qian, and †John A. Reizes *Graduate School of Biomedical Engineering, University of New South Wales; and †Faculty of Engineering, University of Technology, Sydney, Australia Abstract: Finite-volume computations are described for laminar flow in the hydrodynamic bearings supporting 2 different versions of the impeller of the VentrAssist rotary pump. Pressure boundary conditions are taken from prior computations of turbulent flow in the whole pump with frictionless sliding of the impeller on the inside of the pump body. By investigating various impeller positions, the true ride height is determined. Net lift and combined drag from all 8 bearings of the 4-bladed impeller are com- pared with predictions based on 2-D theory. The compu- tations also reveal the extent of net force and moment acting to move the impeller away from its nominal axis of rotation. Key Words: Rotary pump—Laminar flow— Hydrodynamic bearings—Computational fluid dynamics. The VentrAssist rotary cardiac assist device (Micromedical Industries Ltd., Chatswood, New South Wales, Australia) is a centrifugal pump for apico-aortic connection. Instead of using thrombo- genic pivots or power-drawing magnetic suspension, the impeller is supported hydrodynamically when rotating by lubrication flows in the thin spaces be- tween itself and the pump body. To this end, the impeller has 4 wide blades each offering a broad surface close to the conical top and another close to the flat bottom of the body. The volume of each blade is used to house rare-earth magnets such that the impeller is also the motor rotor as described by Watterson et al. (1). The impeller has gone through a design evolution that started with blades having parallel leading and trailing faces. Qian and Bertram (2) described pre- liminary work on the bearings of this 1.3 impeller. This article describes the ultimate outcomes of that work and compares the findings with those reached by application of similar methods to the 2.8 impeller, which has a more complex blade shape. These 2 im- pellers are illustrated in Fig. 1. METHODS It is convenient first to describe the calculations based on the simpler and more regular geometry of the 1.3 impeller, then to pass to the modifications needed to cope with the 2.8 blade shape. The overall strategy is to perform 2 entirely separate computa- tions, taking results from the first as input to the second. Both computations utilized the finite- volume code CFX-TASCflow 2.8.0 (AEA Technol- ogy, Harwell, U.K.). The first computation is of the flows in the whole pump, using that which the TAS- Cflow documentation (3) calls frozen rotor mode. The flow is assumed to be turbulent, and the blades are assumed to slide without friction on the conical top and flat bottom of the pump body. In this calcu- lation, there is no flow between the blades and the pump body. This computation also is used to predict the overall pump performance (4). But for this pur- pose, the results needed are the pressures predicted at the sliding boundaries of the domain. These boundaries are the edges of those blade faces that create the lubrication flows. Received January 2001. Presented in part at the 8th Congress of the International So- ciety for Rotary Blood Pumps, held September 6–9, 2000, in Aachen, Germany. Address correspondence and reprint requests to Dr. C.D. Ber- tram, Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia 2052. E-mail: c.bertram@ unsw.edu.au Artificial Organs 25(5):348–357, Blackwell Science, Inc. © 2001 International Society for Artificial Organs 348