Natural convection from a circular cylinder in oscillating flows has been simulated by projection method with two dimensional exponential stretched staggered cylindrical meshes. Present numerical results are validated by comparing the heat transfer results of free convection over a circular cylinder to published experimental and numerical results. The effects of wave directions, amplitudes, frequencies and buoyancy forces on the enhancement of heat transfer have also been presented. Based on turning points of the curves of the overall Nusselt numbers versus Reynolds numbers, the heat transfer can be divided into three linear regimes (conduction, laminar convection and turbulent convection dominated regimes) and two non-linear transient regimes. The valid ranges of the governing parameters for heat transfer enhancement have been identified. The effects of wave directions, amplitudes, frequencies, and buoyancy forces on the enhancement of heat transfer are also investigated. The effective ranges of the governing parameters for heat transfer enhancement are identified Copyright © 2013 by ASME.