A computational and experimental comparison of two outlet stators for the Nimbus LVAD

Two designs of an outlet stator for the Nimbus axial flow left ventricular assist device (LVAD) are analyzed at nominal operating conditions. The orig inal stator assembly (Design 1) has significant flow separation and reversa l. A second stator assembly (Design 2) replaces the original tubular outer housing with a converging-diverging throat section with the intention of lo cally improving the fluid dynamics. Both stator designs are analyzed using computational fluid dynamics (CFD) analysis and experimental particle imagi ng flow visualization (PIFV). The computational and experimental methods in dicate: 1) persistent regions of flow separation in Design 1 and improved f luid dynamics in Design 2; 2) blade-to-blade velocity fields that are well organized at the blade tip yet chaotic at the blade hub for both designs; a nd 3) a moderate decrease in pressure recovery for Design 2 as compared wit h Design 1. The CFD analysis provides the necessary insight to identify a s ubtle, localized flow acceleration responsible for the decreased hydraulic efficiency of Design 2. In addition, the curiously low thrombogenicity of D esign 1 is explained by the existence of a three-dimensional unsteady vorti cal flow structure that enhances boundary advection.