A study on the flow field around a circular cylinder placed in a rectangular orifice jet

A long circular cylinder with the diameter of 20 mm was placed in an air jet, issuing from a rectangular orifice with the short side, h, of 3 mm and the aspect ratio of 10. The cylinder was settled on the symmetrical plane of the jet flow along the long side of the exit. The impinging distances between the jet exit and the front surface of the cylinder, xi, were varied within fifty times of the short side length. The jet exit velocity was kept constant at 24 m/s and the Reynolds number, based on the short side length, was about 4900. It was found that the mean and fluctuating(rms) pressure profiles around the circular cylinder showed remarkable changes with the impinging distance and the position along the cylinder axis, z. The value of fluctuating pressure at the stagnation, being different from that of fluctuating velocity of the free jet, was large even at the vicinity of the jet exit. The negative pressure region, formed on the front surface of the cylinder, alone diminished clearly at a position of z over the impinging distance of xi/7<5. The saddle-backed velocity profiles for the orifice jet as well as the diminishment of the negative pressure region along z-axis might result in the off-axis distributions of the drag per unit width. The drag per unit width at z/h = 3.3 of xi/h = 5 was increased up to 2.4 times of the drag at z/h = 0. The coefficient of total drag on the cylinder was estimated 1.16 at the jet exit and 0.76 at xi/h = 50.