FULLY-DEVELOPED INTERMITTENT FLOW IN A CURVED TUBE

Fully developed intermittent flow in a strongly curved tube was numeri cally simulated using a numerical scheme based on the SIMPLER method. Physiological pulsatile how in the aorta was simulated as intermittent flow, with a waveform consisting of a pulse-like systolic flow period followed by a stationary diastolic period. Numerical simulations were carried out for the following conditions: Dean number kappa = 393, fr equency parameter alpha = 4-27, curvature ratio delta = 1/2, 1/3 and 1 /7, and intermittency parameter eta = 0-1/2, where eta is the ratio of a systolic time to the cycle period. For alpha = 18 and 27 the axial- flow profile in a systolic period becomes close to that of a sinusoida lly oscillatory flow. At the end of the systole, a region of reversed axial velocity appears in the vicinity of the tube wall, which is caus ed by the blocking of the flow, similar to blocked flow in a straight tube. This area is enlarged near the inner wall of the bt:nd by the cu rvature effect. Circumferential flow accelerated in a systole streams into the inner corner and collides at the symmetry line, which creates a jet-like secondary flow towards the outer wall. The region of rever sed axial velocity is extended to the tube centre by the secondary flo w. The development of the how continues during the diastolic period fo r alpha higher than 8, and the flow does not completely dissipate, so that a residual secondary vortex persists until the next systole. Acco rdingly, the development of secondary flow in the following systolic p hase is strongly affected by the residual vortex at the end of the pre vious diastolic phase, especially by stationary diastolic periods. The refore, intermittent flow in a curved tube is strongly affected by the stationary diastolic period. For eta = 0 and 1/5, the induced seconda ry flow in a systole forms additional vortices near the inner wall, wh ereas for eta = 1/3 and 1/2 additional vortices do not appear. The cha racteristics of intermittent flow in a curved tube are also strongly a ffected by the length of the diastolic period, which represents a peri od of zero flow.