Tc). The used method is validated against the existing numerical results and an excellent agreement between the results was found. The flow is assumed to be two-dimensional and air is chosen as a working fluid. The effect of different parameters such as Rayleigh number (Ra =103, 104, 105, 106), different position of obstacle inside cavity (H=L=0.1, 0.4, 0.7) and different angle of obstacle (θ'=00, 900, 1800, 2700) at different aspect ratio (AR =0.2, 0.4, 0.6, 0.8) on fluid flow and heat transfer inside the channel are investigated. The results showed that by increasing the Rayleigh number and increment of aspect ratio, the rate of heat transfer is increased. Also, enhancement the distance of obstacle from left and bottom walls of cavity, lead to decrement rate of heat transfer and the maximum values of mean Nusselt number are shown respectively at angles of 0, 90, 270, 180 degrees.]]>