Annular Couette type blood shearing devices have been used for analysis of blood damage related to device induced shear stress. Two important factors in predicting cell damage are the magnitude of stress and the duration of exposure to the stress. Several previous devices for blood damage analysis consist of concentric cylinders with one cylinder rotating and the other held stationary. This generates a Couette flow between the cylinders. In a typical apparatus, the shear stress can be controlled by varying the rotation of the inner cylinder and the exposure time can be controlled by controlling the axial velocity of the fluid through the device. The higher the rotational speed the higher the magnitude shear stress. However, apparati are susceptible to a flow instability at high rotational speeds. This flow instability is characterized by toroidal vortices and may be predicted by the Taylor number, which is related to the fluid viscosity, gap and rotational speed. If the critical Taylor number is exceeded, Taylor vortices will exist. Taylor vortices are undesirable because blood cells may become entrapped in these vortices and increase exposure time thus leading to distorted hemolysis data. Because shear stress is also a function of the gap and rotational speed, the avoidance of Taylor vortices places limits the shear stress and exposure times that can be achieved in this type of a device. Changing the gap size and shape affects the formation of Taylor vortices. In this study several variations of the gap shape and size of the flow path of a blood shearing device are investigated numerically in order to find the geometry that has a physiologically relevant range of shear stress and exposure time while avoiding Taylor vortices. The proposed design will be used in future studies to study the effect of shear stress on the blood for a certain exposure time.

Publication Date


Document Type


Student Type


Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)


Steven W. Day

Advisor/Committee Member

Risa J. Robinson

Advisor/Committee Member

Karuna Koppula


Physical copy available from RIT's Wallace Library at QA911 .R48 2013


RIT – Main Campus

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