Effect of yaw on forced convection heat transfer from a circular cylinder

Wind tunnel experiments encompassing ten angles of yaw between 0 (crossflow) and 60° yielded Nusselt numbers extending over the range of free stream Reynolds numbers from 9000 to 70,000. Supplementary experiments were also performed in which the heating pattern at the surface of the cylinder was varied and in which major alterations were made in the boundary layer on the wind tunnel wall. These experiments established that the measured Nusselt numbers were truly representative of the uniform wall temperature boundary condition and were independent of the characteristics of the wind tunnel boundary layer. It was found that as the cylinder was yawed relative to the crossflow orientation, the Nusselt number at first decreased, attained a minimum at a yaw angle of 15°, and then increased to a broad maximum which occurred in the range of yaw angles between 30 and 45°. Thereafter, the Nusselt number decreased with increasing yaw. Furthermore, the data did not obey the so-called Independence Principle, according to which the Nusselt number is supposed to be a unique function of the Reynolds number based on the component of the free stream velocity normal to the cylinder. As a further supplement to the heat transfer experiments, the pattern of fluid flow adjacent to the cylinder surface was visualized by means of the oil-lampblack technique.