Effects of Pulsating Strouhal Number on Heat Transfer around a Heated Cylinder in Pulsating Cross-Flow

An experimental study was conducted to investigate the effect of pulsating Strouhal number, Sr_p, on flow and heat transfer around a heated cylinder in a pulsating cross-flow. The averaged Reynolds number was kept at 400 while the oscillatory Reynolds number was changed from 40 to 300. Pulsating Strouhal number, Sr_p, ranged from 0 to 1.37. Two marked peaks of the mean Nusselt number were observed at approximately Sr_p =0.2 and 0.6. Flow visualization experiments revealed that twin symmetric vortices were periodically formed behind the cylinder at Sr_p corresponding to the 'lock-on' of the shedding of vortices. From the velocity field measured by particle image velocimetry (PIV), it was determined that the flow reversal approaching the back surface of the cylinder was intensfied by the twin vortices. This flow reversal caused heat transfer enhancement on the back surface of the cylinder.