Transition to Turbulence in a Periodically Intermittent Flow

Abstract

The blood flow in the ascending aorta comes to rest after the aortic valve closure until the next ejection phase starts, and the flow in the aortic arch is close to an intermittent flow rather than an oscillatory flow. In order to reveal the nature of turbulence in the aorta, the measurements of turbulence in the intermittent air flow in a straight tube were made by a hot-film anemometer. The periodically intermittent flow was generated by the piston connected with a step-rod. The resting period was varied in a range of between 0.3 and 10 sec, but the velocity wave patern of the piston was fixed. The turbulence intensity, skewness and kurtosis for the intermittent flow depend entirely on the resting period. For the resting period of 0.3 sec, the nature of turbulence resembles that of pure oscillatory flow. As the resting period becomes larger, a significant intermittence of turbulence appears in the longer range of phase. The turbulence in the intermittent flow with a relatively long resting period turns out to be close to that in the ascending aorta.