The effects of the lock-in phenomenon on heat transfer characteristics and structures of Karman vortex behind a highly heated cylinder in pulsating flow driven by a loudspeaker were investigated experimentally. The diameter of the cylinder is 4 mm, while the heat flux of the cylinder is q = 89.0 kW/m2. Based on the cylinder surface temperature, the shedding vortex frequency, and the added pulsating flow frequency, the heat transfer characteristics can be classified into three regimes: lock-in, transition, and dissipation. In the lock-in regime, the heat transfer rate was enhanced by 2% compared to the non-pulsating condition. Despite the lock-in phenomenon not occurring, the surface temperature of the cylinder decreases with increasing pulsating frequency in the transition regime, which means pulsating flow works to intensify heat transfer. In the dissipation regime, the surface temperatures are equal to those of non-pulsating conditions. This means that high-frequency pulsating flow does not work to enhance the heat transfer rate. To conclude, pulsation flow is useful to enhance heat transfer, especially in the lock-in condition. However, the small-time scale pulsation flow is not it.
CHIBA et al. (Wed,) studied this question.