Dean vortex stability using magnetic resonance flow imaging and numerical analysis

Magnetic resonance flow imaging using flow encoding with spin warp imaging was used in three dimensions to measure velocity profiles and the dynamic b ehavior of centrifugally-induced (Dean) vortices in curved tube flow. Exper imental measurements were compared with numerical simulations obtained from the solution of Navier-Stokes and continuity equations using a commercial finite-element package. Effects of flow, rate and geometry, and the ratio o f the tube radius to that of curvature on the stability of Dean vortices we re studied. Twisting and bifurcation of vortices increased with increasing flow rate and radius ratio. A six-vortex pattern was measured experimentall y and predicted numerically. Additional wall shear rates, due to Dean vorti ces, were estimated from velocity measurements in the cross-sectional plane . A phase diagram was constructed to establish conditions for the existence of two, four or six vortices as a function of flow rate and curvature. Exp erimental observations were compared with numerical results obtained from t hree types of finite-element grids. The full-tube grid without symmetry pla nes was most predictive for vortex bifurcation, while the pseudo-cylindrica l full-tube grid with a plane of symmetry gave best results for sheer rates . Results from the numerical analysis agreed qualitatively well with the MR I measurements.