07. Turbulence and Flow Instabilities

It has been confirmed previously that when swirling is applied to the flow in a pipe, heat transfer is significantly enhanced compared to pressure loss in the transition regime. In this paper, fluctuation pattern of the heat transfer measured using high-speed infrared thermography was re-observed and considered the factors that enhance the heat transfer in the transition regime from perspective of turbulent vortical structure. The observation revealed that the advection direction does not match the inclination angle of the streaky structure, whose inclination angle is around 5°⁓10° larger than the advection angle. This suggests the formation of cyclonic vortices, which may cause the dissimilar heat transfer enhancement in which heat transport dominates over momentum transport. In addition, the relationship between the change in the flow field by applying the swirl and the dissimilar heat transfer enhancement was discussed based on the facts that could be inferred from the measured data.