MEMS sensor to resolve spatial variations in shear stress in a 3-D bifurcation model

We demonstrate a microelectromechanical systems (MEMS) sensor that provides unprecedented spatial resolution to resolve circumferential variations in shear stress in a scaled-up model of a symmetric bifurcation. The Reynolds numbers for the bifurcation model, based upon the average flow velocity and the tube diameter upstream of the bifurcation, ranged from 6.7 down to 1.34, and correspond to microcirculation levels typical of arteriolar vessels. At these low Reynolds numbers, the wall shear stress was higher within the bifurcation and lower downstream from the bifurcation. Skin friction coefficient values, representing local wall shear stress values normalized by the upstream dynamic pressure, varied by a factor of two or more depending upon the circumferential position within the bifurcation. At a Reynolds number of 6.7, the skin friction coefficient on the lateral interior wall of the bifurcation along the 270deg plane was C_f= 7.1 (corresponding to a shear stress value of 0.0061 dynes/cm²). At the top of the bifurcation along the 180deg plane, C_f= 13 (0.0079 dynes/cm²), and at the medial wall along the 90deg plane, C_f = 10.3 (0.0091 dynes/cm²). The measured skin friction coefficients at various positions correlated well with values derived from an exact Navier-Stokes solution of the flow within the bifurcation