Numerical investigation of impeller design variation on mechanical blood pump hemodynamics

Abstract

Mechanical heart assist device is an emerging treatment for end-stages of heart failure which is an alternative to heart transplant due the shortage of heart donors. Despite the clinical success of “Left Ventricular Assist Devices (LVAD)”, the development still continue as new designs are progressively being tested to address the ever existing complications. Developing these blood pumps requires determining a balance in providing adequate pump performance while giving attention to possible occurrence of blood damage. This study utilized a proposed design concept of a hybrid bearing system and evaluate its’ merits of adapting the concept from a perspective of computational fluid dynamic (CFD) approach. Two design parameters were chosen for this study; the conical shape of the impeller bottom that functions to provide both radial and axial stability and secondly, the inclusion of a groove profile intended to complement the system as a hydrodynamic bearing as well as improving washout flow. Four model variations were constructed from the design parameters for comparison with the number of mesh between 8.9 to 9.8 million nodes. Menter’s Shear Stress Transport (SST) turbulent model was used to simulate 3 different operating speeds (2000 rpm, 3000 rpm, 4000 rpm) at 5 varying flowrate (3, 4, 5, 6, 7 L=min). Evaluation involved assessing the model variants based on several performance criteria. Ranked selection method was used to rate and select the better performing model variation with a good compromise between the level of blood damage potential (hemolysis index) and the pump performance although heavier emphasis on blood damage was chosen as a priority. In the analysis, CFD results showed that the inclusion of conical shape has negligible effect on pump head with a minor 0.8 percent difference, however it does present a potential area of stagnant flow, reducing washout by 28.3 percent. The groove profile along with conical shaped impeller present high shear stress region at the impeller bottom area that caused an increase in hemolysis index by an average of 15.4 percent. Ranking and selection of the model variants resulted in the flat groove configuration scored as the best performing configuration that gives the good compromise of pump performance and hemolysis.