غلامرضا ایمانی

In this paper, numerical simulation of fluid flow and heat transfer characteristics of a porous cylinder subjected to a transverse oscillation in subcritical crossflow are studied for the first time. As such, the effects of Darcy number, ?10?^(-6)?Da??10?^(-2), reduced frequency, 0.2688?f^*?1.075, dimensionless amplitude, A/d=0.5 and 1, and Reynolds number, 5?Re?40 on the problem are investigated. It is revealed by the results that for an oscillating porous cylinder even at subcritical Reynolds number of 40 the vortex shedding surprisingly develops behind the cylinder for cases with Da??10?^(-4), f^*=1.075, and A/d=1. Furthermore, it is shown that this subcritical vortex shedding always happens at the lock-in situation. The oscillation of the cylinder is shown to always increase the lift and drag coefficients compared to the stationary cylinder. According to the results, interestingly, the average drag coefficient increases with increasing Darcy number at intermediate Darcy numbers (?10?^(-4)?Da??10?^(-3)). It is concluded that two mechanisms boost the heat transfer rate, namely the vortex shedding, which is the case for the low Darcy zone at the highest frequency and amplitude of the oscillation, and the flow penetration which is of more importance to the high Darcy zone. In conclusion, the maximum increase in the average Nusselt number is achieved at the highest values of the frequency and amplitude which provides 18%, 28%, 51%, and 81% heat transfer enhancement compared to the stationary cylinder for Da= ?10?^(-6) ?,10?^(-4), ?10?^(-3) and ?10?^(-2), respectively.