Pulsatile flow in a conical tube.

Abstract

The present study of pulsatile flow in a conical tube, although fundamental in nature, may be used to determine blood flow characteristics in cannulae. For the experimental study, a transparent conical tube was connected to a mock circulation loop. Pulsatile flow was supplied by a pump ("artificial heart"), with controlled "pulse rate" and systolic time period ratio. Tests include flow visualization, pressure measurement with miniature piezo-resistive pressure transducers and velocity measurement with a two-component, frequency shifted, fibre optic, laser Doppler velocimeter. Flow visualization has revealed the formation of a high speed jet in the core of the conical tube during "diastole" as well as the appearance of separated and recirculating regions near the inclined wall. The formation of weak backflow ("regurgitation") was also observed during "systole", especially immediately upstream of the valve. Pressure variation in the tube was fairly complex, containing substantial fluctuations that are caused by the opening and closing of the valve. Measurements of the axial velocity along the centerline of the test section demonstrate an emerging downstream asymmetry of the "active" part of the velocity cycle, which is a clear indication of separation and recirculation in the conical tube. A large set of measurements have been analyzed in order to describe the detailed flow pattern during the cycle. Reverse flow took place at both the conical and the straight sections of the tube. However, in the conical section, the flow shows more unsteady and complex variation during the cycle. Also, the reverse flow near the wall region in the conical section occurred earlier in the diastolic phase, which is a clear indication of separation caused by the expansion. (Abstract shortened by UMI.)