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We experimentally examined influences of microbubbles on generation of a localized turbulent puff in a circular pipe flow. Central velocity fluctuations in the pipe flow measured by LDV were utilized to distinguish status of flows: It enables to distinguish ‘decaying disturbances’ that emerges on intermediate state in between puffs and laminar flows. Forty trials to investigate status of flows were performed at different intensity of perturbation controlled to create turbulent puffs at fixed Reynolds number, Re = 1,900 for both of single phase and microbubbly liquid with volume fraction lower than 0.018%. The results indicated that the adding microbubble enhances creation of turbulent puffs and prevents decaying of disturbances. This means that dilute microbubble promotes flow transition. Finally, we quantify the results by using two methods which are based on a velocity dropping value and correlation coefficient. These methods make it possible to classify status of flows in a pipe.

Effect of Microbubbles on the Creation of Localized Turbulence in a Circular Pipe Flow